If Humans Touch Mars

Like Lascaux - Another Tale of Human Missteps?


Copyright © Robert Walker (UK). All rights reserved.

Cover picture shows Pat Rawlings, courtesy of NASA "20/20 Vision," illustrating an astronaut searching for fossils on Mars. (Higher resolution version of cover)

First published on December 2016. You can also read this on kindle. For my other kindle booklets, see my author page on Amazon.com

The main sections in this book are

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In science fiction, artist's impressions, movies and the popular imagination, there is no question about it, humans touch Mars. Bold and brave astronauts explore the planet from Mars bases in pressurized rovers and spacesuits. They look for fossils from the past, and present day life. They scale cliffs, adventure into caves, and dig deep in their search for life. Perhaps also they eventually learn to live there themselves. That's how I thought about it too until around the turn of the century, when I started to become aware of the many ramifications and consequences that follow, if humans touch Mars.


Artist's impression of human astronauts exploring Mars - credit NASA / Pat Rawlings

As these brave astronauts explore Mars, their bases and rovers would leak Earth microbes into the Mars dust wherever they go, every time they open an airlock. Spacesutis also are typically designed to leak at the joints, for mobility. So their spacesuits would also continually leak Earth microbes wherever they walk around on the surface.

The dust is light and easily moved in the wind even in the near vacuum of the Mars atmosphere. Typical wind speeds that Mars dust storms can carry a dust particle hundreds of kilometers in a few hours. The occasional global dust storm lasts for weeks and it takes months for all the thick dust clouds to fall back out of the atmosphere. If there is anywhere that Earth life can survive on the surface of Mars, or open to the surface, then the trillions of hardy microbial spores streaming out from a human base would surely find it eventually, and irreversibly change the planet (for more on this see How could this work on Mars with dust storms and a globally connected environment? ).

That's especially so after a Columbia space shuttle type crash of a human crewed spacecraft on Mars. The planet could potentially be irreversibly contaminated with Earth life. If so, this means that what we do there now would impact on us, our descendants, and all future civilizations in our solar system for the entire billions of years future of Mars.. Why don't the explorers in Star Trek and the many movies, books and TV series about exploration of other planets have these problems? Is it perhaps because the stories are the product of a science fiction and movie maker's imagination? After all, they are not based on any actual experience of exploring another world.

Could we get a future news story: "Debate over Moldy Mars is a Tale of Human Misteps"?

We have made so many mistakes on Earth. I start this book with the example of the many things that went wrong with our attempts to preserve the Lascaux cave paintings. Could the same happen some day with Mars? Might we some day read an article in the Washington Post, similar to a recent one about the Lascaux caves as: "Debate over Moldy Mars is a Tale of Human Missteps"? If so, is this something we can foresse in advance and prevent?

At least nowadays scientific news stories about Mars sometimes mention these issues. But still, it's too often brushed over quickly. almost as an afterthought. For instance in a recent Sky at Night program in the UK, Life on Mars the presenters briefly covered the need to protect Mars from Earth life. They also talk about the impossibility of doing that with humans on the surface. But it was treated as a rather minor matter. The discussion starts about sixteen minutes into the program. The presenter ended by saying (around twenty minutes in)

"So, that's the balance of the argument, extreme caution to protect the pristine Martian environment, versus our desire for the most important scientific discovery of all time. If it were up to me, I think the scientific benefits outweigh the contamination costs. Maybe none of this is going to matter, in a few years time. Last month president Obama announced a human mission to Mars by the 2030s. Elon Musk wants to get there much sooner, with hundreds or even thousands of people forming permanent Martian colonies. Now humans are messy, leave trails of cells, and DNA wherever we go. So when that happens, who is going to really care about a few bacteria?"

(The episode is no longer available to watch online even in the UK, but it is available to buy and watch online, I think probably for UK residents only.)

In other words, the idea is that our present situation is frustrating, and once we send humans there we will no longer need to be bothered about protecting the planet, because the die will be cast. With Mars irreversibly contaminated with Earth microbes, then with a huge sigh of relief, at last, we can go about exploring Mars much as we explore Earth (though in spacesuits of course).

That argument may seem persuasive to you, if you haven't looked into it in detail. Indeed even many scientists think this way. Kudos to the BBC for raising the issue at all however, as the idea of planetary protection is so often ignored completely as soon as the discussion turns from robotic to human missions. Another video raising these issues is this one from VSauce Is it okay to Touch Mars? which they did for the national geographic series on humans to Mars. I got the idea for the title of this book after listening to their video and this book is in a way a response to it. It covers some of the same issues that they cover (starting nine minutes in),, but there is so much more to be said.

Raising awareness - fossil optimists and early life enthusiasts

As you read this book,you may be surprised to learn

We have a long way to go by way of raising awareness of these issues, and I hope to help with this book. Before we can make the right decisions we need a clear understanding of what the issues are.

Many of us, without even thinking about it, are "fossil optimists" as I characterize it in this book. The cover photo shows this fossil optimism in artworrk done for NASA by Pat Rawlings. We are used to learning about past life from fossils and expect it to work in much the same way on Mars. Enthusiasts, including scientists, even search the Opportunity and Curiosity photos for what they think may be fossils of past Mars life.They are searching rocks that are unlikely to have had any life for more than three billion years. Nearly all Earth macro fossils date from the last half billion years, apart from some stromatolites and other fossils that are ambiguous and took a lot of proof before they were accepted as life. To look for clear unambiguous macrofossils in Gale crater is to show optimism that life on Mars had a three billion head start on Earth. Such fossil optimism is not absurd, indeed you can come up with some suprrisingly good reasoning in favour of it, but you can argue the case both ways.

Many professional astrobiologists are "early life enthusiasts". Their professional focus and instrument design is mainly orientated towards life similar to whatever existed on Earth over three billion years ago. Such early life may very well even indluce precursors of DNA based life, so small that you can't see it at all not just with a magnifying glass but even with the best of optical microsopes. They don't expect to find macrofossils at all. Instead they pin their hopes on the ability of the Mars conditions to preserve organics for billions of years. But they expect this signal to be weak, degraded, mixed in with organics from other sources, and only present in a few rare locations. They also expect that they will need to drill to depths of several meters to find it. For this reason they think that in situ searches with sensitive biosignature detectors are the way ahead for the search for past life. Present day life is likely to be elusive too for different reasons.

Value of humans in space

In my other kindle books and booklets, and my articles, I've written a fair bit about the value of space resources, and the many ways that humans can contribute in situ to exploring the solar system. I also argue strongly for the Moon as the obvious place to get started with human exploration. It's not just as a stepping stone to Mars. It's also a place of great interest in its own right, and with little by way of planetary protection issues to deal with. It's also a far safer place to start. The ISS has "lifeboat" spaceships attached at any time, with enough seats to take the entire crew back to Earth within a few hours in an emergency. On the Moon we can have similar lifeboats to take the entire crew back to Earth within two days with al the fuel and food for the journey. On Mars or in Mars orbit it can be up to two years to get back in an emergency, which may be a step too far right now.

"MOON FIRST Why Humans on Mars Right Now Are Bad for Science", available on kindle, and also to read for free online.

Case For Moon First: Gateway to Entire Solar System - Open Ended Exploration, Planetary Protection at its Heart - kindle edition or Read it online on my website (free).

I argue that with our experiences on the Moon we can learn about the value of humans in space, and the practicalities of how to stay healthy there. We can also learn to survive in a more self sufficient way, for months and then years at a time, before we need resupply from Earth. Oonce we've done that on the Moon, then it will be practical and safe to send humans not just to Mars but to the Venus clouds, Mercury, asteroids and further afield, for instance to Jupiter's Callisto, just outside its dangerously intense radiation belts. We can explore the Mars surface from orbit in an immersive way. This is similar to exploring a three dimensional virtual world in a computer game, but this time the world explored is real. This could be a more direct way of experiencing the Mars surface than in clumsy spacesuits in the dim brownish gray light of the Mars surface. We can gain experience of this on the Moon first. Telepresence like this may be a great way to explore the Moon too. This virutal way of touching Mars is an exciting and adventurous alternative vision for humans in space which is also safer, and has none of the irreversible and possibly devastating consequences for science of landing humans on the Mars surface directly.

I thought it's best to say that from the outset as I've found in the past that my readers sometimes see my articles as an attempt to stop humans from exploring space. Far from it, I'm a science fiction geek and long term enthusiast for humans in space since the time of Apollo, which were exciting missions that I followed keenly as a teenager. Humans on Mars are not the problem. The problem comes with the microbes that accompany us, in the air, in our water, and indeed on and in our bodies too, trillions of microbes that can't be removed or we'd die. These include microbes capable of living in extreme environments too, as many of these extremophiles retain their ability to survive in more ordinary conditions too. They can manage just fine on and in our bodies, and on the surfaces of our spaceships. Even the organics that make up our bodies, our food, human wastes etc could be a problem in the event of a crash on Mars by confusing searches sensitive to a single amino acid in a sample. If we explore Mars via telepresence, we can be there in person without these consequences of touching Mars.

Human settlement and exploration - hugely positive or hugely negative - it all depends how it is done

Of course many of my readers will be keen on human settlement in space. I argue that this has potential to be hugely positive or hugely negative. It depends very much how it is done, and it may be a good thing that we are likely to start with few humans in space.. I'm no advocate for sending large numbers into space as fast as possible. After all think what the consequences would be if we had the likes of ISIS and North Korea in space colonies with space technology far advanced over ICBMs. I cover this in my Case for Moon First under:

I argue also that settlement can have hugely positive consequences if done well and can help protect and sustain Earth, move heavy industry into space and provide power and resources that may help us in the future.

It's a similar situation for human exploration without settlement, though for different reasons. That also can be either hugely positive or harmful, and that's what this book is about, the especial case of the impact of in situ human exploration of the solar system on science and the search for life. Mars is the one place in the inner solar system most vulnerable to Earth microbes. The same issues also apply for Jupiter's Europa and Saturn's Enceladus with their deep ice covered oceans connected to the surface. Humans can probably help a lot with their ability for in situ decision making. But we have to be careful to look at the downsides as well as the upsides of humans "on location" in the solar system, and find out how best to plan our explorations.

So let's get on to the book. What are the possible consequences and ramifications if humans touch Mars?


Touching Mars

We love to touch things. If you put a sculpture in an art gallery and say "please touch" you can guarantee that both children and adults will touch it. So it's natural that we want to touch other planets. But there are plenty of things we can't touch on Earth, not just sculptures and works of art in art galleries. The Lascaux cave paintings for instance,


Photograph of the Lascaux paintings by Prof Saxx.

The original painters touched the caves. Many of us would love touch them also, feel the texture of the rock that they were painted over. But not only is nobody permitted to touch them - we have to take care even about going into the caves at all. The warmth, humidity and carbon dioxide from the breath of visitors have all taken their toll. Fungi and black mold are attacking the paintings.


The purple markings in this photograph show damage to the paintings resulting from human presence

The Lascaux cave was first found in the 1940s by four children with their dog, and opened to the public immediately after WWII by the owners who enlarged the entrance, added steps and replaced the cave floor sediment with concrete. The humidity, carbon dioxide and warmth of all the visitors took their toll leading to microbes, fungus and black mold growing. Even though the cave has been closed to all except occasional specialists, it is too late now to restore it completely to its original condition.

Attempts to fix the many issues lead to one more misstep after another. For instance, after a white fungus spread over the floor and up the walls, the scientists took care to photograph every single painting in detail, to keep track of the damage. What they didn't realize is that the bright lights for the photographs were themselves damaging the cave, encouraging the growth of black mold, which is now a major issue there with black spots spreading over the cave. For details see the Washington Post article: Debate Over Moldy Cave Art Is a Tale of Human Missteps. In a recent conference, climatologists say it is possible to restore the original environmental conditions of the cave. But the microbiologists say that it is not possible to restore the pre 2000 microbial conditions. They say that the only way forward has to be to find an equilibrium which incorporates the new species of microbes introduced to the cave by human visitors.

Will we some day see a similar headline?

"Debate over Moldy Mars is a Tale of Human Missteps?"

Enthusiasts who are keen for humans to land on the Mars surface as soon as possible tend to brush these concerns aside.

"We are going to Mars, that's what humans do, always push beyond frontiers, whatever they are".

You ask what about planetary protection from Earth life, and they say

"Oh, that will get sorted out, the scientists will find a way. We will go there in the 2020s or 2030s.

We care about protecting Mars and will do whatever they ask us to do, but we can't be stopped. They just have to find a way to make it work for us, to protect Mars while at the same time permitting humans to land on the surface."

The idea that scientists might ask them not to land on Mars at all is something they may dismiss or even find outrageous, as I've found in many conversations. Yet there are places on Earth where humans can't go. We can't go to the Lascaux cave without great care. When new cave paintings or etchings are discovered nowadays, the cave is immediately closed off to the general public and only a few scientists can visit.

New cave etchings in the Iberian peninsular, as much as 14,500 years old. They were immediately closed off to the general public to preserve them. They will use technology instead to give us the best view of them possible without directly visiting them.

And there are some places humans can't go at all. However much you might want to visit the lake Vostok in Antarctica, kilometers below the surface of the ice, you can't go there. Even if you are a billionaire, even if you fund the expedition entirely yourself, you would not be permitted to go down in a sub and explore it looking for hydrothermal vents and whatever unusual lifeforms live there. If you did that, you'd introduce surface life to the lake, so confusing scientific study of a body of water that has been cut off from the surface possibly for millions of years. Scientists would dearly love to explore this lake, but they haven't yet found a way to do it.

Microbial ethics

So, could we harm Mars as much as we did with the Lascaux cave, or perhaps more so? The debate about this often centers around ideas of "microbial rights" and microbial ethics. Of  course, these are not rights for individual microbes, but if we discover life on Mars, in whatever form, does it not perhaps have the right to evolve undisturbed by interference from humans? Might we even decide to restore early Mars conditions to help the life to evolve undisturbed by us?

Some argue that microbial life on another planet deserves a "biorespect" from us independently of whether we can actually make use of it or find it of value to ourselves. The astrobiologist Charles Cockell has written extensively about this, for instance see what he says about it in "A Microbial Ethics Point of View" in the Ethics of Space Exploration.

Whatever ones views on that, our present reason for protecting planets from Earth life is a much more practical one. We do it to protect the science value of other planets. We may be on the point of making the greatest discovery in biology, perhaps since discovery of evolution and the helical structure of DNA. It just makes sense not to make this hard for ourselves, or even impossible, by introducing Earth microbes first, to confuse the search. I'll look at issues with looking for present day life later, but first, let's look at how microbes from Earth could confuse the search for past life on Mars.

Searching for fossils on Mars in the popular imagination

In popular imagination, this is probably how most would think we would search for life on Mars. Pick up rocks, crack them open, and find fossils. 



Image by Pat Rawlings, courtesy of NASA "20/20 Vision," illustrates search for life on Mars,

Caption: "Did life ever exist on Mars? If so, the best evidence may be fossils preserved in the rocks. Geologists and biologists will one dya explore Mars, piecing together the history of the planet and perhaps its ancient life".

After all that is how fossils of earlier lifeforms were first found on Earth. Here is a drawing of Mary Anning - the Victorian fossil hunter who is described in the popular tongue twister 

"She sells sea shells on the sea shore"

Illustration of Mary Anning selling fossils

She used to dig up fossils of ammonites and belemnites and sell them in her fossil shop at Lyme Regis.


Sketch of Mary Anning by De la Beche, gathering fossils. Her hammer is made of wood clad in iron. It's displayed in Lyme Regis’s Philpot Museum. Details from page 78 of this World Heritage assessment of the Dorset and East Devon fossil beds.

And indeed, if we found something like this, the search would probably be over, could anything like this form except through life processes :):
Fossil ammonite from Lyme Regis museum, photo by Kimtextor
Or if we saw this, well what else could it be but a past lifeform?

Pen and ink drawing of a Plesiosaur by Mary Anning, from 1824. This and more photos and video on the BBC Mary Anning famous people site for children.

There would be no question about what we had found if we found something like this on Mars

Mars was only as habitable as Earth for the first few hundred million years. After that it  got more and more hostile for life over much of its surface. So did it ever develop plants or creatures large enough for us to see as fossils? Well there is at least one thing in its favour. It may well have had an oxygen rich atmosphere early on, over three billion years ago - the Gale Crater deposits are between 3.3 and 3.8 billion years old. While exploring them, Curiosity found manganese oxides. These can only form in highly oxygenated water. 

The dark material cleared of dust in this photograph consists of manganese oxide, which filled a fracture and was resistant to erosion. The three dots you see in the bottom left enlargement are drill holes made by Curiosity to analyse the material. This manganese oxide could only form in highly oxygenated water. So indeed the ammonites and indeed fish and pleisorus would have plenty of oxygen on Mars. The reason that Mars is red is because all the iron on its surface rusted long ago. So it's not so astonishing to find evidence of oxygen rich water there in the past, but it was unexpected even so.

We don't know how the oxygen got there. It could be the result of ancient Mars microbes which developed photosynthesis as that's how similar manganese deposits formed on Earth. But Mars had another way to make oxygen. With no magnetic field, the solar storms could split water vapour in its upper atmosphere. The lighter hydrogen then would escape into space making its atmosphere oxygen rich. See How a weird Mars rock may be solid proof of an ancient oxygen atmosphere

There are three main periods of Mars geology:

  • The early Noachian and pre-Noachian periods, which had an extensive sea (though possibly often ice covered) over the Northern hemisphere of Mars. That entire hemisphere is lower in elevation than the southern hemisphere.
  • The Hesperian period of volcanic eruptions and extensive flooding and a second sea three billion years ago.

  • The Amazonian period of more localized flooding, though with a second sea at one point. This is followed by billions of years of cold dry conditions with occasional small flows of water and some flooding. The climate is quite variable depending on the tilt of Mars, the eccentricity of its orbit, and local effects of impacts. At times the atmosphere is thick enough for pure water to be liquid though at present ice everywhere is at or close to boiling point as soon as it melts. Mars is still in the late Amazonian period.

Fossil optimists and early life enthusiasts

Did life ever evolve on Mars? We don't know. If it did, was it ever abundant? It's quite possible that it could evolve yet never be abundant, for instance if it only evolved near hydrothermal vents and never developed photosynthesis or any other way to spread any further. Did it ever develop to macroscopic life? Most fossils from Earth which are large enough for us to see on Earth date back to the last half billion years, out of over four billion years of evolution. Is it possible that multicellular life got off to a much faster start on Mars?

You can argue both ways. Perhaps difficult and changing conditions stimulate evolution. For instance, perhaps the "Cambrian explosion" of multicellular life happened as a result of the snowball Earth just before.

Mars' orbit is much more variable than Earth's, under the influence of the other planets. At times it gets very eccentric. It's somewhat a mystery, how it had liquid water at all in the early solar system, perhaps it had strong greenhouse gases such as methane in the atmosphere. When its orbit was at its most eccentric, maybe it had oceans that were frozen over every time it was furthest from the Sun, then melted a year later when closest to the Sun, especially when its lower altitude northern hemisphere summer coincided with times when it was closest to the sun. So what would that do to evolution? And what about the solar storms and cosmic radiation? Also the frequent meteorite impacts - Mars had many more large impacts than Earth in the very early solar system at the times of its oceans.

So - Mars was a tougher place for life to evolve. Perhaps this accelerated evolution. Or on the other hand it might have kept knocking it back so that it never evolved far, keeping life on Mars at an early stage. The evolution would have to be accelerated hugely to have multicellular life there already three billion years ago. If you are optimistic about macro fossils on Mars you could go with that hypothesis to back up your hopes.

If evolution on Mars proceeded independently of Earth evolution, it would be a great surprise if life on Mars was at exactly the same stage of evolution as life on Earth. However it's rather amazing how large the differences are between possible hypotheses for past and present day life on Mars.

If you are a fossil optimist, and expect to find fossils in Hesperian age deposits on Mars such as Gale Crater that are easily recognizable as fish, or plants or similar - that means that you think that Mars had its equivalent of the Cambrian explosion more than three billion years ago.


Opabinia - if Mars evolved creatures as advanced as this already in the Hesperian period, it's evolution would be about two and a half billion years ahead of Earth evolution.

Modern stromatolites in Shark Bay, Western Australia - if Mars had stromatolites in the Hesperian era then its evolution was similar to Earth life as the earliest possible stromatolites date back to 3.7 billion years ago on Earth, these 1-2 cm high putative stromatolites found in Greenland. However ancient stromatolites are hard to identify conclusively and there might be much debate before they are accepted as such

Acritarch - these organic microfossils are also very ancient , date back to between 1.4 and 3.2 billion years on Earth. The name was coined by Evitt in 1963 and means "of uncertain origin" and the term is used for any microscopic organic fossils that can't be assigned to any other classification. They may be associated with green algae, some kind of a cyst or resting state. Since nobody is sure what they are then they are classified by their structure instead. For instance as prismatic, spindle shaped, egg shaped, spiky like a thorn bush, etc. See also wikipedia article on Acritarch.

If Mars evolution reached a similar stage to Earth evolution then we might find similar organic microfossils on Mars. If so, there might be a lot of debate about what they are. We could expect similar announcements to these about Mars: "Organic-walled microfossils in 3.2-billion-year-old shallow-marine siliciclastic deposits" or "Microfossils of sulphur-metabolizing cells in 3.4-billion-year-old rocks of Western Australia" followed by much discussion of what they were, and indeed about whether they were life or not too. That's often a matter of debate for early Earth putative microfossils, whether they were life or not. It would be even more so on Mars.

So if there are easily recognizable macrofossils in Hesperian deposits on Mars, then evolution there has to be at least two and a half billion years ahead of Earth life. If it reached an equivalent stage of evolution to Earth life, we might find the equivalent of those ambiguous fossils from 3 billion years ago on Earth.

It's also possible to argue that evolution on Mars evolved much later, with many setbacks. It might even still survive on Mars which would put evolution there three to four billion years behind Earth. Though on the plus side the stable geology of Mars without continental drift and the extremely cold conditions there may make early life easier to study there.

I don't think we can distinguish between those and many other possibilities on the basis of what we know so far about Mars.

What about thick deposits of life, like our oil rich shales?

What if Mars life was abundant enough to develop thick deposits of oil rich shales? Or the equivalent of chalk which is made up entirely of shells? Could it have deposits consisting of meters thick remnants of ancient life in some form or another?

Mars may have been habitable in the early solar system for hundreds of millions of years in relatively stable conditions, and continued to have seas and lakes for over a billion years. So, if evolution got off to a rapid start, and evolved very rapidly, if it had its Cambrian explosion already more than three billion years ago, that would be plenty of time to build a thick deposit of oil shale in ideal conditions.

If we found something like this, even without the multicellular life fossils, just the remains of single cell life but in deep meters thick beds of organics, our task would be easy:

Fossils in Ordovician oil shale (kukersite), northern Estonia (Ordovician period)

However we haven't found anything like this yet. Maybe conditions on Mars were never favourable for creating thick deposits of life based organics. Or, it could be that they were washed out by the later floods, and what's left was destroyed by surface conditions. Maybe Mars still has deposits like this, many meters below the surface beyond the reach of the cosmic radiation? Any surface deposits, even meters thick, would soon be degraded to just water vapour and other gases by the cosmic radiation over the billions of years timescale. So we'd only spot them if they were unearthed in the recent geological past. There are plenty of craters but that would only unearth them if the deposits are very abundant.

At any rate if those deposits exist, we don't know where to look for them yet. There is no sign of them from orbital observations, and our rovers haven't spotted anything like this yet either.

Even multicellular fossils would be hard to find

Even if Mars had birds, and fish, in the early solar system, the chances are that we wouldn't have found any signs of them yet.

This picture shows Archaeopteryx. It was hard to find. They had to search through tons of quarry material to find a few thin flakes with Archaeopteryx preserved.

You could send a rover to Earth and set it to explore rock formations in our desert regions for decades, and it might never spot a single fossil, depending where you send it. Or it might find a layer of chalk or similar with hundreds of them.

How would we recognize fossils on Mars?

The other problem is that we don't know what to look for on Mars. If we found a fossil archaeopteryx it would be obvious. Even a fossil multicellular plant. But for billions of years, the only macro fossils on Earth were microbial mats and stromatolites. So, what if we find these?

These are now known to be early stromatolites. But it took a lot of work and evidence, particularly the evidence of organics caught up in the material of the stromatolite fossil itself, before they were accepted as such.

The later stromatolites were easier to identify but these very early ones were particularly challenging.

There are many formations on Earth that look for all the world as if they were some fossil lifeform, such as this.

Baryte Rose from Cleveland County, Oklahoma, photograph by Rob Lavinsky

If Curiosity found this on Mars, I'm sure many people would be convinced it was a fossil. But no. It's a "Desert rose" - a crystal like structure that can form in desert conditions.
Enthusiasts have found many strange shapes on Mars that they think may be fossils. For some remarkably compelling examples, see for instance Mars Fossils, Pseudofossils or Problematica?”, by Canadian scientist Michael Davidson. But we have to use the Knoll criteria to evaluate them. It's not enough that they look like fossils:
"The Knoll criterion is that anything being put forward as a fossil must not only look like something that was once alive -- it must also not look like anything that can be made by non-biological means.”

Oliver Morton, author of Mapping Mars: Science, Imagination, and the Birth of a World

This criterion is named after Andrew Knoll, author of “Life on a Young Planet" a book about past Earth life, who is on the Curiosity mission science team.

We will be very lucky indeed if we find a lifeform on Mars that we can conclusively identify as living just by its physical shape. Even if it turns out that the planet had stromatolites, or even multicellular fish and birds, in the past, the problem is finding them. We are more likely to find something like this - potential fossil signs of past life found on Curiosity photographs by geobiologist Nora Noffke

To her expert eye these look like trace fossils of microbial mats. But another geobiologist Dawn Sumner thinks they are just the result of normal erosion processes. See Follow Up - Signs of Ancient Life in Mars Photos?

To add to the difficulties, Mars has very different geological conditions from Earth. As an example, it doesn't have chlorides, but it has abundant chlorates, sulfates and even hydrogen peroxide. There are only small amounts of oxygen in the atmosphere, but the surface is far more highly oxidized than Earth's surface. It also has some geological processes that we know only happen on Mars such as the processes that involve dry ice (e.g. the dry ice geysers and dry ice blocks sliding down slopes). Dry ice is a significant causation factor in many Mars geological formations and it is never a factor on Earth at all. Even the sand formations are created by winds that blow the dust in ways that they wouldn't on Earth because of the low gravity and the near vacuum atmosphere. The low gravity also lets geological structures form as a result of wind erosion that would be unstable on Earth. And there is no water. And because of the low pressure, the fastest winds on Mars would be just strong enough to gently move an autumn leaf. The dust storms only are able to lift up the dust because it is so fine, as fine as cigarette ash. It also has much larger temperature variations, able to change between the freezing point of dry ice and melting point of water and above in the same day.

Mars is such a different world, with such different geological processes, that it won't be surprising at all if we find unusual hard to identify geological formations on the Mars surface. So, no, it's not very likely that an astronaut could pick up a fossil on Mars and identify it as such.

Practical science reasons - why small quantities of present day life can confuse the search

So, if there is life on Mars, how will we find it and recognize it? If we can't expect to identify it conclusively by recognizing fossils, well perhaps we identify it through the organics. After all, that's how the ancient stromatolites on Earth were eventually proven to be fossils rather than geological formations.

So, past life on Mars is likely to be identified through organic biosignatures initially (the same is also true for present day life as we'll see). Once recognized that way then we may be able to identify them as fossils too, but it's unlikely that we recognize them first through their macrostructures. The enthusiasts who want to send humans to Mars tend to brush this off, the question of how we identify past or present organics from life on Mars, and say either

"No need to worry, Mars life will be identical to Earth life so it doesn't matter what we bring there"
Or they may say even in the same talk:
"No need to worry, it will be easy to tell the difference between Mars and Earth life, so it doesn't matter what we bring there."                                                                                                                                                                                

And then

"No need to worry, Earth life can't survive on Mars or vice versa. It's like sharks trying to survive in the African Savannah."                                                                                                                                                                                

Zubrin will often bring up all three of those arguments in the same talk as different reasons why we don't need to worry about introducing Earth microbes to Mars. His audience of human spaceflight enthusiasts find these arguments very persuasive and clap him enthusiastically.

I think that perhaps they feel he has covered all bases. Either Mars is so inhospitable to Earth life that it's like sharks surviving in the savannah, or it is so similar that Earth life not only would fit right in but has already got there on meteorites, or if neither of those apply then Earth life would be as easy to distinguish as anthrax by genetically sequencing it. But actually, those are just three of numerous possibilities and indeed perhaps rather unlikely ones at that. So remarkable that you'd want to keep Earth life away from Mars while you study the remarkable phenomenon.

He also talks about the advantages of human astronauts over robotic rovers on the surface, citing an example of a fossil discovery he and a team of others made in Arizona in a Mars exploration simulation. From his log book:

"There is a lesson in all of this for those who think that robots represent a superior way of exploring Mars. With a human crew on this site, impaired by all the impedimentia of spacesuit simulators with the cloudy visors, backpacks, thick gloves and clumsy boots, our crew found petrified wood and a fossil bone fragment within two days. But to do it we had to travel substantial distances, and climb up and down steep hills from which we could take views and map out new plans. We had to search the sites we visited, processing the equivalent of millions of high-resolution photographs with our eyes for subtle clues. We had to dig. We had to break open rocks and take samples back to the station for detailed analysis. In short, we had to do a ton of things that are vastly beyond the capabilities of robotic rovers.

"Sojourner landed on Mars and explored 12 rocks in 2 months. Today we explored thousands. If a robot had been landed at the position of our hab, it would have spent months examining a few uninteresting rocks in the immediate vicinity of the station. It would never have found the fossils."

This turned out to be an interesting discovery, a new place to search for fossil dinosaurs: Scott Williams of the Burpee Museum of Natural History rates it as one of the nations best places to search for Jurassic era fossils.

Demolishing Zubrin's arguments

I go into this in a lot of detail in my Moon First books. But let's look at them briefly here.

  • Yes, Earth life on Mars could be like sharks in the savannah. Or it could be like rabbits or cane toads in Australia. Or like invasive plants like Kudzu or Himalayan Balsam

    The Mala or shaggy haired wallaby, considered as creation ancestors for the Anangu Aboriginal people - are in competition with the introduced rabbit.

    Is competition with introduced Earth microbes on Mars more like sharks competing with lions, or rabbits competing with wallabies. We have many examples of species on Earth that have gone extinct due to invasive species such as rats, cats, etc.

    We can't decide this by using colourful analogies.
  • Yes anthrax on Mars would be easy to detect. But most Earth microbes have not been sequenced. Of an estimated one trillion species of microbes, only ten million species have been identified and catalogued (so 99.999% are not yet identified). Most are hard to cultivate (the so called microbial dark matter) and indeed only about 10,000 have ever been grown in a lab. Of those only about 100,000 have classified sequences. So only 0.00001% of all microbial species on Earth have been sequenced to date. See Largest ever analysis of microbial data (May 2016). So, if a wide range of species of Earth life was introduced accidentally to a Mars habitat then typically only the tiniest fraction of a percent of the species in that habitat could be confirmed as definitely coming from Earth. For the rest of the lifeforms that actually came from Earth, you'd just have to say you don't know.

    Photomicrograph of Bacillus anthracis bacteria using Gram-stain technique. This is one of 100,000 microbes that have been genetically sequenced. Robert Zubrin is fond of using it as an example in his talks. Yes if we found a microbe on Mars that has been genetically sequenced on Earth and we genetically sequenced it, we'd be able to tell if it is from Earth or Mars. But only 0.00001% of Earth microbes have been sequenced. After accidental or deliberate introduction of Earth life to Mars, we can expect to be unsure about the origins of 99.99999% of the species we find on Mars, even if they all originated from Earth.
  • Yes meteorites get to Mars from Earth, on average tons of them every century. But that's an average over timescales of billions of years. The numbers fluctuate hugely, and there are probably no meteorites from Earth arriving on Mars right now. After all we don't get any meteorites from Earth impacts falling back to Earth right now. We get meteorites from the Moon, from Mars, possibly from Mercury but nothing from Earth itself in modern times - not any that actually left Earth, and then came back again.

    Even meteor crater in Arizona wasn't large enough to send ejecta with escape velocity. Rather you need a huge impact like the Chicxulub meteorite impact 66 million years ago. Earth clears its orbit over a period of twenty million years. So that 66 million years old material is probably all gone now. And anyway solar storms and cosmic radiation would sterilize it thoroughly unless buried deep within rocks many meters in size. The best time for a meteorite to get to Mars is a century after the impact on Earth as that's when the first ejecta would get there. And yes there may have been many tons of material arrived from the Chicxulub impact as soon as a century after the impact on Earth.

    The astrobiologists who wrote "Over protection of Mars" think that life on Mars is going to be pretty much identical to Earth life in all respects. But that is a minority view. It could equally well be very different indeed. Their reasoning is that Earth and Mars have shared a lot of material via meteorites. But that only happens after really huge impacts on Earth like the Chicxulub meteorite 66 million years ago.

    Artist's impression by Don Davis of the Chicxulub meteorite impact into a warm tropical ocean. A huge impact like this could send debris all the way to Mars through our thick atmosphere. Remarkably, experiment suggest that some very hardy extremophiles could survive the century in the vacuum, cold, and solar radiation of space as well as the shock of ejection and impact on Mars. However we don't yet have any examples yet of panspermia - transfer of microbes on a meteorite between planets. It is currently a theoretical idea not confirmed by any observations. 
    But then look at the obstacles in the way of a microbe before it can get to Mars by this route. It has to be able to withstand the heat and acceleration of ejection from Earth and impact on Mars. It has to be capable of surviving inside a rock - because anything on the surface would be destroyed - from the heat, and from the UV radiation in space. It has to be able to withstand the hard vacuum of space. It has to withstand the extreme cold of space - so after the heating up and high gravity during the ejection, it then has to survive freezing well below the freezing point of water. Then it has to survive the cosmic radiation and the solar storms of the journey to Mars. Finally once there it has to find a habitat. Remember that to have survived so far, it is deep inside a rock, so if it survives impact on Mars, it's not likely to be dispersed in the dust storms. Most of Mars is very cold, dry, no water, so though there may be favoured habitats there, it has to find them. How does it do that from inside a rock?

    Then, it has to be pre-adapted. This is the same problem as Zubrin's sharks surviving in the Savannah. Maybe it could evolve to live on Mars, and microbes can evolve quickly, but it won't have that opportunity unless it can survive right away when it lands on Mars.

    In the case of Mars this probably means it has to be pre-adapted to tolerate perchlorates (which are pervasive in the dust, highly oxidizing) and the hydrogen peroxide. If it is photosynthetic life it has to tolerate high levels of UV light in the sunlight too. And of course have to be anaerobes able to survive without oxygen. It also has to be able to cope with the near vacuum atmosphere and the UV radiation if it is a photosynthetic lifeform. Or it has to cope with the sulfates in soda lake type conditions if it is able to find its way somehow into a habitat there. What's more, if there is native Mars life, it has to compete with it too, so has to be better adapted than Mars life, or at least, as well adapted, right away from the moment it arrives on Mars.

    It's remarkable that scientists think that there may be microbes that could survive all this. Many microbes may be able to survive on Mars but just couldn't survive the rigours of the journey there, or have much chance of finding a suitable habitat once there, or would not be pre-adapted to the habitat once it is found.

    It may well have happened. But if so, it might not have happened for billions of years. The easiest time for this is during the first few hundred million years during the late heavy bombardment. But was Earth life back then hardy enough to be transferred to Mars on meteorites (or vice versa)? The most recent chance of this happening was 66 million years ago so any Earth life that survived there has evolved independently for at least that long. and the bottom line here is that so far we have no confirmed case of panspermia to base the ideas on. It is just theory. If there is any life transferred on meteorites, then surely most life on Earth wouldn't be able to do it. For more on this, see Microbial Survival Mechanisms and the Interplanetary Transfer of Life Through Space.

    Meanwhile microbes on a human occupied ship don't have to survive any of these rigours of a journey to Mars. They get a comfortable ride inside a human occupied spacecraft, protected from UV light, and extreme cold or heat, in a rapid journey to Mars, Once they get to Mars then they can survive not just in the human ship but also in marginal habitats outside it. For instance every time humans open an airlock then air from inside, along with moisture, flakes of human skin, hair and other debris, and numerous spores will be dispersed out into the Mars landscape. This will also happen whenever they use spacesuits as spacesuits are designed for mobility which at least with spacesuit designs so far also means that they are also designed to leak air constantly through the joints. The microbes that leak from spacesuits and airlocks can feed on the dead remains of their predecessors. And then also you have trillions of them. They aren't hidden inside rocks but dispersed in the atmosphere right away. They may fall into shadows, so protected from UV light, can get caught up in the dust and spread throughout Mars in the dust storms. They have a far easier time than their panspermia cousins hidden inside rocks for a century on the journey to Mars in the cold vacuum and ionizing radiation conditions of interplanetary space.
  • Advantages of human astronauts for fossil hunting on Mars - for one thing, this all depends on Mars having macrofossils. Even early stromatolites are likely to be tiny (one or two cm in size), hard to recognize, and controversial once found. Dinosaur bones and other macrofossils, which an astronaut could recognize easily seem very unlikely (though not impossible).

    Also, he is not comparing like for like there. Before we send humans to Mars, whether to orbit or on the surface, then we would need broadband communications with Mars. Astronauts in orbit around Mars could explore it with binocular vision and even from Earth we could look at millions of images streamed back reconstructed to make a 3D landscape that we can explore at leisure to look for fossils. Future rovers would be more robust and capable than Sojournor. And we'd have 2D binocular vision, haptic feedback and many other technological improvements that we can do with existing technology given an increased level of funding and commitment. Or this may happen anyway through development of technology. More on this below.

    Also if the search is for organics, present day or past life, a better analogy might be with LDChip300 (part of the SOLID project). This was an organic biosignature detector developed by astrobiologists with the hope that it may some day be sent to Mars. It uses 300 different antibodies - which together can be used for very sensitive tests for organic biosignatures. They tested it in the "hyper arid" core of the Atacama desert, drilling into the extremely salty "hypersaline" subsurface. From in situ analysis of just half a gram of sample in situ, it found a previously undiscovered microbial habitat two meters below the surface. Humans had explored the desert for decades and never found it.

    Microbes in salt crystals two meters below the ground in the Atacama Desert, discovered using SOLID by researchers from the Center of Astrobiology in Spain and the Catholic University of the North in Chile. SOLID is one of several extremely sensitive instruments, low mass, which astrobiologists hope one day can be sent to Mars for in situ search for life there. Image credit Parro et al./CAB/SINC

I agree, Zubrin's arguments may seem persuasive at first, especially if you are keen for humans to touch Mars. But once you reflect on those points, they may not seem quite so compelling. For more on this see How a human spaceship could bring microbes to Mars - Zubrin's arguments examined in my MOON FIRST Why Humans on Mars Right Now Are Bad for Science. So anyway I leave that as something to reflect on.

So how easy or hard will it be to search for life on Mars?

Though macrofossils, shale deposits or similar would be great, it would take a lot of optimism to pin your hopes on that possibility. First, present day life is likely to consist mainly of microbial life, or at most lichens, even if multicellular life evolved in the past. That's because similarly inhospitable locations on Earth such as the hyperarid core of the Atacama desert and the Mc Murdo dry valleys in Antarctica have only microbes, and sometimes lichens in them. As for past life, then it would have had to get off to a very fast start to reach the stage of macrofossils so long ago.

So, both past and present day Mars life is likely to be very hard to detect and also hard to distinguish from Earth life. The first problem is that life may be there only in minute traces. Modern life may be scarce and hard to find, because it is so inhospitable. It would be life at the edge, only just surviving. Past life may have been destroyed long ago except in a few favoured patches which may have only a few trace amounts of organics, and not only might it be microbial, it might be early life, that hasn't yet evolved to be as large as a modern microbe on Earth.

I'll talk about present day life later. But first, let's look at why past life is likely to be hard to find and how introduced Earth organics can interfere with the search.

ALH84001 as an example of what we may find in the search for past life on mars

Some of you may remember when president Clinton announced the possible discovery of past life on Mars in a meteorite, the famous ALH84001. And then perhaps the anticlimax afterwards when later investigations were not able to prove that it was definitely life? It hasn't been disproved either. The scientific jury is just out on what it is at present with some scientists arguing in both directions.

Many astrobiologist think that ALH84001 is a much more likely model for what we may find in the search for life on Mars than fossils you could spot by eye or with a lens or even an optical microscope, or shale oil deposits. The life in this meteorite, if that is what it was, was so small it could only be seen with an electron microscope. 

If it is life, then the supposed cells seem to be too small to include all the cell machinery of modern life. The discovery of the possible life in this meteorite lead to a 1999 workshop to try to figure out if such small things could be alive. And the answer was yes, though present day life simply can't be so small and include all the machinery to reproduce, early life could be as small as tens of nanometers in scale, far beyond the optical resolution limit of 200 nm. 

So, well to the ordinary person, not an astrobiologist, and especially if you are keen to "touch Mars" or at least for someone to do that, if not you - perhaps your thought at this point is

 "Well what's the big deal. Just a few microbes, so small you can't see them in a microscope?

This will only interest a few microbiologists, and apart from them, who cares if we mess up their chances of finding this life. It is so uninteresting that it shouldn't stop humans from doing what we want to do, land boots on Mars and touch Mars."

Well, if you look at it like that, it might not seem that interesting. But if you look at it another way there's something much more interesting about this than another obscure microbe that happens to be smaller than any others found to date (if Mars life does turn out to be like this).

RNA world and the shadow biosphere

To understand how exciting and interesting this discovery would be, first you need to know how similar all modern life is. It might seem that modern life is widely diverse - the fish, fungi, trees, birds, animals, starfish, octopuses. Adding a few microbes too small to see hardly seems likely to add to that diversity. However underlying all that life is an almost identical structure. If you look deep inside the cells of every living creature on Earth, seaweeds, plants, amoebae, microbes of all sorts, bird, animals, they all look pretty much the same at level.  This amazingly complex process is going on in each and every one - and at roughly the speed of this visualization. This is not an actual video of the interior of a cell, but scientific art that depicts it as accurately as possible, a scientific visualization of the cell processes.

All Earth life uses the same language here. To find a new form of life would be like discovering your first new language if all you have ever known before is English (say) and you knew in principle that the words must come from other languages but you have never heard any other language or seen any other language written.

What's more the interior of the cell is the same or similar in many other ways too.  For instance, consider carotenoids - these are the pigments that make carrots, peppers and poppies red, yolks of eggs yellow, flamingos and shrimps pink, and autumn leaves red or orange. Carrots, poppies, fungi and trees can make the carotene for themselves. This substance is used not just as a pigment but to protect chlorophyll and to convert blue and green light in the range 450 to 570 nm in the visible spectrum into light at the right frequency for chlorophyll to use. So it's an important part of photosynthesis. 
Most animals and insects can't make this substance. Flamingos, birds etc get their carotene by eating plants. But the plants, fungi etc all use the same identical biochemical pathway to produce it. And as it turns out, in a surprising discovery, some red pea aphids can make their own carotene.

Credit: Zina Deretsky, National Science Foundation

They got this ability through horizontal gene transfer from a fungi. This didn't transfer the actual carotene. Rather, it transferred just the instructions for making carotene, which when incorporated in the cells of the aphid lead to it making carotene also. What's more, it does it through a complex biochemical pathway that is identical in both the fungus and the aphid. For details of how they made this discovery, see First case of animals making their own carotene and for techy background on carotene and the biochemical pathway by which it is made in cells, see Carotenoid Biosynthesis in Arabidopsis: A Colorful Pathway.

This horizontal gene transfer is an ancient mechanism and works between organisms that had their last common ancestor back in the early solar system. It might even work with modern Mars life if it uses DNA too, and we are related, even if our last common ancestor is billions of years ago. In one experiment 47% of the microbes (in many phyla) in a sample of sea water left overnight with a GTA conferring antibiotic resistance had taken it up by the next day

All present day life on Earth uses RNA and DNA and it all uses the same complex translation method to convert DNA to RNA and then the RNA to proteins and many other biochemical pathways are identical. Modern life all depends on ribosomes made up of a mixture of RNA and protein, as catalysts. The main reason modern cells can't be any smaller than around the optical resolution limit of 200 nm is because the ribosomes are so huge and because they have to be able to translate DNA to RNA constantly and RNA to proteins, which all adds to the complexity of the cell and so to the minimum amount you have to have in a cell to make it function.

Early life just couldn't have started like this as the whole thing is far too complex to form spontaneously. It probably didn't have DNA. It may have had only RNA (or some other biopolymer). It may have used the far smaller ribozymes (which are made up of fragments of RNA) for the catalysis. Based on those ideas they suggest that early life could have had cells as small as 50 nm across.  It may not have needed proteins at all. It may have consisted largely of RNA in different forms - the so called "RNA world hypothesis".

This leads to the idea of a shadow biosphere on Earth. This idea was quite popular a while back. It got tied with nanobes, structures that visually resemble life:

from "New life form may be a great find of the century" (1999) The nanobes discovered on Earth are mysterious. Nobody knows if they are life, non life, or something in between.

The idea was that these tiny structures could be a form of life that we miss because our tests for life target DNA based life. What if these were RNA world cells, and we just don't spot them because they only use RNA and don't have proteins or many of the materials that make up the larger cells we are used to? We might have a second "shadow biosphere" living amongst us unrecognized, to this day.

The hammerhead ribozyme made up of fragments of RNA, stitched together with no use of protein chains to make the enzyme - a surprising discovery. This reinvigorated the idea of an RNA world with tiny cells and only needing RNA with no need to translate from DNA.

The cells would only need nucleotides with no need for proteins or amino acids and would not need all the translation machinery to convert DNA into messenger RNA. As a result the cells could be far simpler than modern DNA life. This is one suggestion for an intermediate stage between the earlier organics and modern life, and is the basis for the RNA world hypothesis.

Stephen Benner and others have suggested that there could be RNA world organisms still here today, undetected because they have ribozymes instead of ribosomes. That's the Shadow Biosphere hypothesis. The theory has not yet been confirmed on Earth.

However the RNA world hypothesis is also an alternative theory for the small cell like structures in ALH84001. Whether or not those are indeed RNA world cells - if the earlier life has been made extinct on Earth - it might still be present on Mars. If so it could be vulnerable to extinction due to whatever made it extinct on Earth.

Well so far nobody has been able to prove that this shadow biosphere exists still on Earth, either now, or in the past. But even if it doesn't exist on Earth and any traces from the past have long been erased here, it may exist on Mars, or it may have been on Mars in the past, and remnants of it still survive there.

The idea that the structures in ALH84001 might be these RNA world cells was suggested originally by the fourth panel in Size Limits of Very Small Microorganisms: Proceedings of a Workshop (1999), convened after the announcements of ALH84001. Now that scientists have found alternative ways the structures, magnetite, and organics could form without using life, based on unusual conditions on the Mars surface, this meteorite is no longer thought of as proving the existence of past life on Mars. But it hasn't disproved it either, and the  jury is still out on whether the structures in ALH84001 are life. In "Towards a Theory of Life" in the book "Frontiers of Astrobiology"(2012, CUP) by Steven A. Benner (notable as the first person to synthesize a gene amongst many other accomplishments) and Paul Davies.

"The most frequently cited arguments against McKay's cell-like structures as the remnants of life compared their size to the size of the ribosome, the molecular machine used by terran life to make proteins. The ribosome is approximately 25 nanometers across. This means that the "cells" in Alan Hills 84001 can hold only about four ribosomes - too few ... for a viable organism.

"Why should proteins be universally necessary components of life? Could it be that Martian life has no proteins? ... Life forms in the putative RNA world (by definition) survived without encoded proteins and the ribosomes needed to assemble them. ... If those structures represent a trace of an ancient RNA world on Mars, they would not need to be large enough to accommodate ribosomes (Benner 1999). The shapes in meteorite ALH84001 just might be fossil organisms from a Martian "RNA world".

If we find early life, precursors to Earth life, then it can't possibly work in the same way. Transfer the genes for carotene and it won't be able to make carotene because the cells won't be complex enough, and won't even be able to cope with DNA. So how did they work?

We can't make a living RNA world cell. There is no way we could make modern DNA based life either, if we didn't have it already. We can tinker with it, even add an extra base pair, but the simplest living cell is way way beyond anything we could make from scratch from inorganic chemistry, if we didn't have it already. Our experiments in randomly combining chemicals in conditions to replicate early Earth can only get us a tiny way. We can't simulate an entire ocean left to evolve for millions of years. 

So, there isn't really much we can do to explore these ideas of early life, except actually find it, or find other forms of life that may shed light on what is possible. There is another way also to see that we must be missing a huge amount of knowledge about early life.

Half of the pages of book of evolution have been torn out

This was an idea some researchers had to plotted the increase of complexity of DNA. They found a way to ignore junk and duplicated DNA so that they count only what is essential to the genes of the organism. They found that as life increases in complexity, it follows a near straight line on this plot, through many different changes of structure of organism, from the prokaryotes, to the Eukaryotes with nuclei, worms, fish, and mammals. It's a log plot so this straight line means that it always takes about the same amount of time for the complexity to double.

They traced the timeline back, expecting it to cross the zero line at the time of origin of life, and found that the zero line is nearly ten billion years ago. That's over twice the history of the Earth.

This diagram shows the complexity of the DNA as measured using the number of functional non redundant nucleotides. This is a better measure of the genetic complexity of the organism than the total length of its DNA. Some microbes have more DNA than a human being - much of that used for other purposes rather than for genetic coding, the so called C Value Enigma. Measuring it this way deals with that issue.

Notice that the prokaryotes; the simplest primitive cell structures we know; are well over half way between the amino acids and ourselves. Eukaryotes are cells with a nucleus to store the DNA, and prokaryotes don't have a separate nucleus.

So, either evolution started before the beginnings of our solar system (perhaps brought here by impacts on another planet around another star that passed through the collapsing nebula as our solar system was forming) - or else - evolution was far more rapid in its early stages. Both are plausible. The straight line may just show the characteristic slope for DNA based evolution so earlier life could have evolved far more rapidly.

Either way, you'd expect that as many stages of evolution were needed to get from non living chemistry to the most primitive known cells without a nucleus (prokaryotes), as were needed to get from them to modern mammals. We are missing steps there as radical as the step to cells with a nucleus, multicellular life, creatures with a backbone, warm blooded animals and mammals.

How did early cells work? How did they evolve all the complexity of modern life? How did they get to the two biopolymers RNA and DNA? How did the translation system by which RNA is converted to proteins evolve? There is much that is arbitrary, such as the translation table by which triplets of RNA base pairs get converted to amino acids to make proteins. What about the cell walls and internal structures of cells? Astrobiologists have lots of ideas but have no idea how it actually happened. Nor can they create any novel lifeforms however primitive to test out the ideas. They just don't know how to combine RNA, ribozymes etc to make something that actually works.

So - that is one thing we might be able to find on Mars. If we found something like this, it would be revolutionary, the biggest discovery in biology of this century most likely. We definitely have a possibility of finding out about early evolution of life on Mars.

Life on Mars dancing to a different tune

We'd have a different dance of life from Mars to compare with the dance followed by all Earth life.

If independent in origin, it would have its own versions of DNA, mRNA, ribosomes, RNA polymerase, mitochondria, cell walls, lipids, proteins, gogli apparatus, lysosomes, microtubules, and all the other things that make up the complexity of modern living cells.

RNA polymerase used to decode DNA to mRNA, present in all living cells.

Golgi apparatus - essential organelle in most Eukaryotes

Ribosome translating mRNA into a protein

Microtubules, strands that stretch through cells, a bit like the corals in a coral reef.
ET microbes, if independent in origin, would have a completely different "ecosystem" of these structures.

 One analogy that I've heard is that if you are a cell microbiologist studying the interior of a cell, it is so complex and unique it's like studying an entire ecosystem. So, imagine that you have been brought up in the African savannah - with its grasses and trees and elephants and antelopes. You've never seen a marsh or a forest, or a beach. All your life you've lived in a hut in the African Savannah, never traveled more than a few miles from your hut, and that's the only thing you've ever known. In this analogy this is like the interior of a cell on Earth, any cell from any living organism or microbe here.

View of Ngorongoro from Inside the Crater

Then one day someone takes you to the sea shore, with its fish, shellfish, seaweeds, and sea anemones, and perhaps they take you on a dive to see a coral reef.

A Blue Starfish (Linckia laevigata) resting on hard Acropora coral. Lighthouse, Ribbon Reefs, Great Barrier Reef. Photo by Richard Ling

Here I'm using the analogy, that the interior of a cell is so complex it resembles an entire ecosystem.

The "ecosystem" of the interior of an ET microbe could differ from the "ecosystem" of Earth life, as much as the ecosystem of this Australian coral reef differs from that of the African savannah.

Think how much that would expand your horizons! This gives an idea of what it would be like to find a microbe on Mars with a different biochemistry from Earth life. As boring as it might seem from the outside, just one more small microbe like many others but perhaps much smaller - inside it is as different as a coral reef is from the African Savannah.

So hopefully this can help you see how what the astrobiologists are looking for is not just another boring microbe that happens to be smaller than anything we have on life. In the best case, what I like to call a "super positive outcome" then it could be the most amazing discovery you could imagine, revolutionary for biology, medicine, agriculture, nanotechnology,... There is no way to know how far reaching the implications could be.

Something amazing to discover - but hard to find

But if that is something waiting for us to discover there, most astrobiologists don't expect it to be an easy thing to find.  Some of the things that make it so hard to know if the ALH84001 meteorite has traces of life or not is that

  • Many of the organics could be produced by non life processes, especially the Polycyclic Aromatic Hydrocarbons (PAH's) 
  • Non life processes could also produce the magnetite crystals found in the sample, which originally seemed so characteristic of life. 
  • The carbonate globules could also be produced by non life processes
  • The possible life structures are so small that most can only be seen with an electron microscope. Could they be artifacts of the process by which the samples were prepared?

We will have those same problems on Mars if we study similar samples there. But at least, if we can keep them free of Earth life, we will know for sure that it is not contaminated by life from Earth. Nearly all the organic carbon in ALH84001 is known to be terrestrial contamination.

But that's not the only problem there.

Organics created on Mars by non life processes

Some of the organics made through natural processes on Mars might mimic biosignatures. Also any biosignatures we do find are likely to be mixed up with organics created by non life processes making the signal weaker and harder to detect, especially since past life is likely to be damaged and degraded.

Organics on Mars could be

How do we distinguish between those different forms of organics? If there are any organics from ancient life on Mars, they will need to be well preserved for us to detect them. The very last thing we want to do is to add in an extra spurious signal from modern Earth life to make our task harder than it is already.

Preservation of past organics

Mars is a great place for preservation of organics in some ways. One of the things that makes it hard to find past life on Earth is that warm organics gradually either break apart (DNA) or as the molecules jostle around in the warm conditions, they spontaneously swap over into their mirror image forms. Just as DNA only spirals one way, the other chemicals used by life such as amino acids occur in just one of two possible mirror image forms.

The Mars surface is very cold, just centimeters below the surface, perhaps cold enough so that some of the amino acids and other organics haven't yet swapped into their mirror image forms, even billions of years later. Also with no continental drift, much of the Mars surface is billions of years old, hardly changed since the formation of the planet.

However there are other things that make preservation of ancient organics harder. The main problems here are that the organics can be degraded by many processes on Mars, they may have been present only in a few favoured spots originally, and the search is confused by a constant influx of organics from meteorites and comets which may have chemical signatures that mimic some life processes.

  • Later episodes of flooding

    Artist's impression of Gale crater as it might have looked during one of its flooding episodes (by Kevin Gill). Curiosity Rover Data Indicates Gale Crater Mountain Used to be a Lake

    Of course, floods like this may make it briefly habitable, but they can also wash out earlier deposits. Especially as the later floods on Mars were often rapid flash floods.
  • It gets supplied by organics from meteorites, comets and created in volcanic processes. These would get mixed with the organics from life which we are looking for. And to make things more confusing, the meteorites often have a chiral signature.
  • n this 2006 analysis the EET92042 and GRA95229 meteorites had chiral excesses ranging from 31.6 to 50.5%.

    GRA95229 - another chrondite, collected in Antarctica, had chiral excesses of +31.6‰ for a-AIB to +50.5‰ for isovaline, while the EET92042 meteorite ranged from +31.8‰ for glycine to +49.9‰ for L-alanine. It's thought that these excesses are extraterrestrial and not due to contamination by Earth life.

    They are certainly not pristine, are altered by water, but they come from Antarctica so less likely to be contaminated, and the mix of amino acids is non terrestrial so they don't seem to be a result of contamination. Also it has 2.5 times greater than typical levels of organics in Antarctica. So these excesses may be extraterrestrial and not due to contamination by Earth life. For a more recent review of this, see the Chemistry Society Review article: Understanding prebiotic chemistry through analysis of extraterrestrial amino acids and nucleobaess in meteorites.

    There are various theories about how meteorites may have got this excess originally, see Circular Polarization and the Origin of Biomolecular Homochirality Whatever the reason, it complicates the search for life on Mars.

  • Chemical degradation of near surface materials by the perchlorates, hydrogen peroxide etc. We know that there must be processes actively removing organics because it should have reasonably large quantities of organics from meteorites and comets and instead it only has small amounts of organics. All the organics found so far probably came from meteorites and comets.

  • Mars was most habitable billions of years ago. This is a long timescale for preservation of organics, during which Mars lost most of its water, had many floods, and changed its inclination, orbital eccentricity, atmospheric density, and climate many times.
  • High levels of cosmic radiation - either originally when the deposit is formed, if it is not buried rapidly enough - or later when it is unearthed again on or near the surface. Every 650 million years you get a 1000 fold reduction in the concentrations of small organic molecules such as amino acids on the surface because of cosmic radiation. So that's a million fold reduction every 1.3 billion years. We may have to dig deep to find life that has escaped this process. Probably at least meters deep. The usual recommendation of astrobiologists is 10 meters deep ideally. ExoMars will be able to drill 2 meters which is enough so that it has a chance of finding evidence of past life.
  • Life is most likely in places that had water in the past. These are the very places where warmth, flooding, consumption of the organics by other lifeforms, and other forms of degradation can happen.
  • We don't yet know which parts of Mars had life in the past. For instance, what if the only life occurred around hydrothermal vents, and it never developed as far as photosynthesis? Then we may need to search ancient hydrothermal events to find it. There are many other ideas about where life might have started, so what if it is only in the place where it first evolved and never got any further, wherever that is?

So, this research suggests it is likely to be far more difficult to find past life than you might expect. It's no surprise that Curiosity hasn't found it yet - it is just not looking in the right way in the right place to find it. It's just searching for past habitability, a brief that it has fulfilled rather well. But the organics it has found already are thought to have come from meteorites or comets. 

Any organics in samples the team for Curiosity 2020 selects to return to Earth are almost certainly going to come from those as well. The Mars surface has a continuous influx of organics ,and meanwhile the surface perchlorates, hydrogen peroxide and the cosmic radiation and solar storms damage and remove whatever organics are there already. It's unlikely that we will find traces of past organics unless we do the search for life and unambiguous biosignatures on Mars itself in situ.

For a clear signal of past life

For a clear signal, for past life, we have to look for life in the right place (e.g. hydrothermal vents, or salt lake deposits or the warm seasonal flows or whatever turns out to be best). And then your sample needs to be:

  1. Preserved quickly (dried out, caught in clays or salt, or the microbes rapidly entombed in fast forming rocks like chert)
  2. Plunged rapidly into freezing conditions (or the chiral signal is lost through deracemization)
  3. Buried quickly, ideally within a few tens of millions of years, to a depth of several meters (or it would degrade beyond recognition through cosmic radiation)
  4. The life wasn't washed out with later floods, or chemically altered or decayed or mixed with other sources of organics, or returned to the surface temporarily for more than brief time periods.
  5. Returned to the surface rapidly (perhaps as a result of a meteorite strike), and did this in the very recent geological past. Or else, your rover needs to be able to drill deep, or search in caves protected from the surface cosmic radiation.

On the plus side, Mars is a huge and varied planet, with surface area the same as the land area of the Earth. There are plenty of opportunities to look for this life on Mars. Surely somewhere on the surface of Mars we will find the ideal conditions leading to preservation of past life, and optimal conditions for present day life.

The downside of this vast search area is that we don't know where to look. On Earth one key to discoveries of early life was the realization that gunflint chert is a "magic mineral" that preserves traces of early life.

Galaxiopsis, one of the fossil microbes found in gunflint chert, which has turned out to be a "magic mineral" for search for evidence of early biology on Earth.

What are the "magic minerals" for the search for life on Mars, in the very different conditions that prevail there? Where are the best places to look? We don't know yet.

We are making a great start with Curiosity. We will find out more with future missions like Curiosity's successor and Exomars. But there are many more steps still to go through. See Habitability, Taphonomy, and Curiosity's Hunt for Organic Carbon

So in short, we can't expect to just land on Mars, go to a likely spot and find a sample of past life on Mars. We may have to search long and hard. And we may have to search for just faint traces of a long degraded signal. That means we may be looking for just a few amino acids in the sample.

If we get any Earth life on Mars it will confuse this search.

The earliest lifeforms, if we can find them are also likely to be smaller than modern cells, of the orders of tens of nanometers rather than the hundreds of nanometers of modern cells. It's impossible that the modern cell in all its complexity arose in one go, That would make it an order of magnitude smaller than the smallest known cells on Earth and well beyond optical resolution.

Then, we don't know what we are looking for, yet. It may be unknown biology. It could be based on XNA (like DNA but with a different backbone) or it could be something else not DNA at all.

  • Likely to be single cell micro-organisms
  • We don't know what it looks like
  • We don't know what chemical signatures to look for
  • It may only form nanoscale fossils, which are notoriously hard to identify as life or non life.

Follow the nitrogen, dig deep and look for biosignatures

The best way to search for early life, as far as we can tell at present, is to search for organics. However the organics are easily confused with organics from non life processes and from space. Eight astrobiologists looked into this in a white paper which they submitted to the most recent decadal review: Seeking Signs Of Life On Mars: In Situ Investigations As Prerequisites To A Sample Return Mission

One of the main conclusions of the white paper was that we should look for organics with nitrogen on Mars. Nitrogenous organics are likely to be rare because there are few sources of nitrogen on Mars. This is important because nitrogen bonds are easily broken and are central to biology as we know it. So even if life on Mars is very different from Earth life, perhaps using different amino acids for instance (see Alien life could use an endless array of building blocks) and perhaps use PNA or some other form of XNA (Xeno nucleic acid) with a different backbone from DNA, still it is likely to use nitrogen if it resembles Earth life. Curiosity recently found evidence of nitrates on Mars, also fatty acids, but that wasn't a detection of these nitrogenous organics.

Once we find these compounds, that's not enough as you also get nitrogenous organics from comets and meteorites and natural processes. We then need to search for biosignatures. We also need to be able to drill below the surface (as ExoMars will be able to do) to the maximum depth possible. That's because our best chance of finding evidence of past life is to drill down below the surface layers damaged by ionizing radiation, ideally to ten meters depth or more (though the two meters depth of ExoMars is a good start here).

Their main points are:

  • Need for increasing mobility, and precision landing, supported by orbital observations, to access the many and varied habitable environments including subsurface, layered sediments, gullies and ice sheets.
  • The "follow the water" strategy should now be followed by a "follow the nitrogen" phase combined with a search for biosignatures.
  • The biosignature search can use exquisitely sensitive in situ electrophoresis techniques to identify and characterize and find the chirality of amines, nucleobases, polycyclics and other essential organic molecules.
  • This search should include drilling to the greatest depth possible for the best chance of success for detecting biosignatures of past life on Mars
  • They recommend that we should do a sample return only after we either identify biosignatures on Mars, or have exhausted all other possibilities by in situ research

If we follow this program we need to send instruments to Mars of exquisite sensitivity to look for traces of past life in situ. Astrobiologists have designed instruments for Mars so sensitive they can detect a single amino acid in a sample.

Nasa's plan for safe zones - based on finding Mars life easily

If we knew where to look, then we could just land on Mars, dig up a well preserved sample of ancient life, and then that answers the question of whether there was life on Mars. Then we find a present day habitat, and find present day life and that answers the question of whether there is present day life there. Enthusiasts seem to imagine it happening like that, pretty quickly. If you find life as quickly as that, and supposing you are content so long as  you discover it first and not so much worried about what happens later as Earth life spreads to Mars habitats - then it's a matter of landing somewhere, making sure the humans don't contaminate too much of Mars too quickly, and then sending out robotic scouts to bring back materials for them to analyse.

That's NASA's current plan - an exploration zone, with the human occupied field station in the center, and robotic spacecraft heading off for in situ study around the perimeter, and returning samples to the center. To them this seems like a good compromise, with humans on the surface, lets humans "touch Mars" but they do their best to limit the effects of the microbes by restricting human movement geographically on Mars.

Here is one example, with the human exploration zone shown close to an area of special interest - the recursive slope lineae or warm seasonal slopes, which may have liquid salty brine seasonally, one of the suggested habitats for present day life on Mars:

See Mission to Mars: The Integration of Planetary Protection Requirements and Medical Support and Mars colony will have to wait, says NASA scientists

The "Safe Zone - cleared for human exposure" is a zone without any present day Mars habitats in it, and a region where you don't mind if there is Earth life introduced to Mars. So, the idea is that the human exploration zone is contaminated with Earth microbes and this is just accepted as a necessary part of human exploration of Mars, but only clean rovers are permitted to travel to the habitats that potentially could host surface life on Mars. They bring samples back to the human base for analysis, or are used to study the regions beyond the zone remotely.

That could work just fine on the Moon. If humans don't travel too far from their base, they will preserve pristine lunar surfaces just a few kilometers away, untouched by human footprints or wastes or debris from the habitat. So long as the rovers can also be sterilized sufficiently in a human base, they could be used in just this way to do clean studies of, say, the volatiles at the poles just a few kilometers from the human base. There is some transport even on the Moon by electrostatic levitation of dust, but most contamination would remain in the landing region.

How could this work on Mars with dust storms and a globally connected environment?

But how can this work on Mars with the Martian dust storms? The main problem here is that microbes can form hardy spores, and on Earth these can survive for long periods of time, hundreds of thousands of years, and in rare cases, millions of years of dormancy. On Mars, they can get into cracks in the fine grains of dust and be partially protected from the UV radiation. And the numerous rocks on the surface will totally protect any microbes that get into their shadows from UV light. Even in equatorial regions, some areas under rocks will be permanently shadowed from UV light.

And then you get these:

This is a Martian dust devil - they race across the surface of Mars picking up fine dust and would also pick up any microbes imbedded in the dust. 

The microbes would be protected from UV radiation by the iron oxides in the dust. HiRISE image from Mars Reconnaissance orbiter, of a dust devil in a late-spring afternoon in the Amazonis Planitia region of northern Mars. The image spans a width of about 644 meters.

The strongest winds on Mars would barely move an autumn leaf. But the dust is also so fine on Mars, as fine as cigarette ash, and easily lifted by these feeble winds. Also, it's made of iron oxides too, which would help to shelter any spores imbedded in cracks in the dust, from UV light.

Then from time to time dust storms will cover the entire planet.

Global Mars dust storm from 2001

This relates to an observation Carl Sagan made Carl Sagan raised in an old paper "Contamination of Mars", back in 1967.

"The prominent dust storms and high wind velocities previously referred to imply that aerial transport of contaminants will occur on Mars. While it is probably true that a single unshielded terrestrial microorganism on the Martian surface ... would rapidly be enervated and killed by the ultraviolet flux, ...  The Martian surface material certainly contains a substantial fraction of ferric oxides, which are extremely strongly absorbing in the near ultraviolet. ... A terrestrial microorganism imbedded in such a particle can be shielded from ultraviolet light and still be transported about the planet."

He continues:

"A single terrestrial microorganism reproducing as slowly as once a month on Mars would, in the absence of other ecological limitations, result in less than a decade in a microbial population of the Martian soil comparable to that of the Earth's. This is an example of heuristic interest only, but it does indicate that the errors in problems of planetary contamination may be extremely serious."

Of course we know much more about Mars than they did back then. But the situation is still the same, the dusts do indeed contain large amounts of iron oxides. We have also found out that some microbes are far more UV hardy than realized in the 1960s. The dust storms and high wind velocities are the same as in the 1960s. The dust does contain perchlorates, which they didn't know back then, but microbes can survive exposure to perchlorates at the low temperatures on Mars.

Some experiments suggest, that Earth microbes could survive at least twelve hours of being blown over the surface within a Martian dust storm. See also Survivability of Microbes in Mars Wind Blown Dust Environment. They could also be transported at night during a dust storm, when there's no UV light, yet still dust suspended in the atmosphere.

The largest global dust storms occur only every 30 years or so. With  wind speeds of 10 to 30 meters per second average for the faster winds during a dust storm, the dust could travel 240 to 720 miles every twelve hours, and some of the dust rises to many kilometers in the atmosphere, and it takes months before all the dust settles. If they end up in a shadow at the end of that, they will then be protected from UV radiation until the next time they get transported by the winds. If the human habitat is positioned close to a special region as in the suggestion by Jim Rummel above, these figures suggest that they might get to a vulnerable region in a dust storm in much less than twelve hours. So, the microbes could get to nearby habitats perhaps quite early on. 

As well as that, any organics including dead microbes can also get transported in the dust. Given the challenge of keeping the samples clean of Earth life, and the difficulty of finding nanoscale fossils and traces of degraded organics amongst the organics from meteorites, comets and non life processes on Mars, how can this approach keep Mars pristine for long enough to complete the search for past life.

Also, do we not have some responsibility to keep Mars free of Earth life for future generations or indeed even ourselves in future decades after the first human landings on Mars? It's hard enough if you only need to worry about microbes that escape from air locks, and from spacesuit joints and such like - and any wastes intentionally released onto the surface. But what happens if a human occupied spaceship crashes on Mars?

Crashes of spacecraft on Mars - robotic or human occupied

Mars is probably the hardest place to land in the inner solar system. If you imagine humans landing much as they did on the Moon - well no, it can't happen like that on Mars. basic problem is that Mars has double the gravitational field of the Moon. To fight against double the gravitational field requires a lot more than double the amount of fuel by the rocket equation (fuel has to carry more fuel), and the lunar module would have no chance at all landing there.

Also as well as that, on the Moon you can orbit as close as you like to the surface and the only problem is that you have to avoid hitting the mountains. You can adjust your orbit, wait for as many orbits as you like until ready, if you have enough fuel you can delay your landing looking for a good place to land (as Apollo 11 did), abort back to a higher orbit if it fails, and with enough fuel you can try again if needed, and take your time about it. A human can pilot a spacecraft to a landing on the Moon by hand, as Neil Armstrong did with Apollo 11. That's impossible on Mars.

On Mars, once you start the landing sequence, and you hit the atmosphere, you are committed. You are streaking through the atmosphere at kilometers per second. Everything after that has to work in a perfect sequence with timings accurate to seconds,, far faster than a human being could react. The result is that a landing on Mars is far more complex than a landing on the Moon or indeed anywhere else in the inner solar system. It should be no surprise if spaceships to Mars crash.

First the aeroshell and aerobraking. Then you need the parachute, because it would just take so much fuel to do all the slowing down using rockets.

See Schiaperelli: the ExoMars Entry, Descent and Landing Demonstrator Module

So then you have to find a way to slow it down from those hundreds of miles an hour to a slow enough speed for a soft landing.

So that’s why you then have the retro propulsion stage for most landers on Mars. But you have to take care because if you do retropropulsion when the parachute is still attached you will get the lander tangled up in the parachute. So you have to release the parachute first before you fire the rockets. So the moment of parachute release is very very important, to get that right. It seems that Schiaperelli for some reason released the parachute a bit too early, which was the start of its problems.

Now even after that, you still are not quite home and dry. The problem is that unlike a landing on the Moon you have no control over where exactly you land. Instead you have a landing ellipse. This is the one for Schiaperelli, 100 km by 15 km

There is no chance at all of steering your landing craft during the landing, except possibly in the last few meters. Up to then, it is dependent on whatever the atmospheric conditions are as you land. The Mars atmosphere is so very thin, a near vacuum, but it also varies hugely in density between day and night and there are lots of variations depending on altitude, temperature etc and it is hard to predict exactly. There’s also the uncertainty of the speed and position of the spacecraft as it enters the atmosphere.

Neil Armstrong could decide exactly where to set down the lunar rover and if necessary just fly a bit further to find a good spot. On Mars you have to be able to land safely wherever you happen to be in that huge landing ellipse. Either that, or you take a risk that if you hit a boulder, that’s the end of the mission.

Viking 1 landed not far from a boulder which would have been the end of the mission if it had landed on it

They deal with that as best they can by choosing regions on Mars that are very flat, ideally you want to have hundreds of square kilometers that are pretty much completely flat with no boulders or steep slopes. That’s why Curiosity had to drive for so long before it got to Mount Sharp. It wasn’t safe to land it any closer to Mount Sharp because it would then risk landing on a big boulder or on a steep slope.

Now there are two ideas of ways to simplify this process. The first is supersonic retropropulsion. That’s what Elon Musk plans to do for SpaceX. It's safer in some ways, it permits a much heavier payload also, but in other ways it is riskier.

Conceptually it is about as simple as you can get. The rocket doesn’t have an aeroshell or parachute or anything. It just decelerates.

Early artist’s impression of supersonic retropropulsion

It slows down by coming in very very close to the surface in the thicker atmosphere at huge speeds. Its rockets switch on when it is still traveling at supersonic speeds. It skims across the surface below the height of the higher mountains. Indeed if landing in the Valles Marineres, big rift valley, rift in the Martian highlands, it would need to skim down between the walls of the canyon. All this time the rocket is firing and it is also affected by the friction of the atmosphere. Finally, it comes to a vertical landing.

SpaceX has actually done this on Earth. Their barge landings of the first stage actually have to use supersonic retropropulsion and what’s more, they can achieve a pinpoint landing as well - when it works. So it can certainly be done, but it is rather risky and tricky to do on Mars with the very thin atmosphere there and the atmosphere far more variable in density than Earth’s atmosphere too.

The other way to do it is to use absolutely enormous parachutes. If the parachute is big enough, you can have a conventional landing just as for Earth. Simply use aeroshell, and then parachute, and parachute down and the parachute will slow you down enough so you get a soft landing.

The problem is deploying those parachutes and making sure they work. You can work it out with computer models, test tiny parachutes etc. But at some point you have to test it with real parachutes. The parachutes on Mars so far were tested by firing rockets in suborbital trajectories and then releasing parachutes and required many tests.

To make even larger supersonic parachutes will require many expensive rocket tests. NASA are working on this with their Low-Density Supersonic Decelerator - Wikipedia

This is just a rough idea of how it works. For more on ways of landing on Mars with supersonic retropropulsion or large supersonic parachutes etc, hear Robert Manning talk about it here Mon, 03/28/2016 - 14:00

Elon Musk's idea is to use supersonic retropropulsion. The rocket lands on the Mars surface in reverse. It has to use the atmosphere for aerobraking, and simultaneously fires its rockets to bring it to a standstill on the surface. The atmosphere is only thick enough for this close to the surface, so it skims down to a landing within a few kilometers to the surface - so close that it can't land on mountainous areas of Mars because the air is so thin. 

Artist's impression of red dragon doing supersonic retropropulsion over Mars, image SpaceX

Elon Musk's fun but dangerous trip to Mars

With this background, it's no wonder that Elon Musk said in his talk to the International Astronautical Congress that the mission to Mars carries a high chance of death for the first would be colonists. See Elon Musk envisions 'fun' but dangerous trips to Mars

"I think the first trips to Mars are going to be really, very dangerous. The risk of fatality will be high. There is just no way around it," Musk said. "It would basically be, 'Are you prepared to die?' Then if that's ok, then you are a candidate for going."

He isn't talking about dangerous as in a scary haunted house or fairground ride, where it's scary but you know that you are in safe hands. It's not the idea that the equipment is inspected and though it seems dangerous, you won't actually be hurt by it. He is talking about dangerous as in something that is much more dangerous than base jumping. You could easily be killed by it for real. And for sure, he may find many people willing to sign on for such a ride. But what would the consequences be for Mars?

It will surely take a while to perfect this technology. Even if say, he has four successful previous unmanned missions, this doesn't prove it is safe. With a 50/50 chance of success for each mission, you can get four successes in a row with a 6.35% probability. So four successes would not show at all conclusively even that it is 50% reliable. Other ideas such as enormous parachutes far larger than any tested to date also have similar issues.

So, if we accept that there is a high risk of a crash, how can you be sure you won't get this sort of thing happening?

Debris from Columbia - broken into tiny pieces by the crash. if something like this happened on Mars, with the debris spread over the surface and dust and small debris and organic materials from the crash carried throughout Mars eventually in the global dust storms - that would be the end of any chance of planetary protection of Mars from Earth life.

With this background, how can we land humans there, without a significant risk of a crash? As for the space shuttle, this would mean dead bodies, food, air, water spread over the surface of Mars and mixed in with the dust, It could then spread anywhere on the planet. This would have an immediate impact on science study near the crash site. Your first assumption, if you found biosignatures near the crash site would be that they came from Earth. That could be devastating for science, especially if the humans crash happens close to somewhere biologically interesting on Mars. And that in turn is likely if the human base is situated in a place where they hope to search for life on Mars, past, or present.

However, it gets worse than that. Because Mars is a connected system through its dust storms, the crash site would be a source for life itself to spread throughout the planet. If there is any life able to adapt to live on Mars, and nay habitats there for it, a crash of a human occupied mission on Mars would mean the end of all planetary protection of the planet.

See also my 

Up until around 2008, many scientists would argue that the surface of Mars is sterile, and that if there is any life on Mars it is deep underground and not connected to the surface in any way. With that background, it seemed reasonable to suppose that anything humans did on the surface wouldn't matter. But that's no longer the situation.

Methane plumes on Mars and deep hydrosphere

Mars, like Earth, gets warmer as you get further below the surface. It might have a hydrosphere, a layer of liquid water perhaps a few hundred meters thick, trapped below thick layers of rock and ice. There's probably ice and then water kilometers below the surface even in the equatorial regions. So, even before 2008, astrobiologists thought that there could be deep down habitats for life on Mars. Then there could be geological hot spots near the surface too. Mars is still geologically active, though not nearly as much so as Earth. Despite many searches, there's no sign of any current volcanic action or hot spots. But there are signs of volcanic eruptions in the Olympus Mons caldera and other volcanic effects as recently as a few million years ago. So there could be hot spots not far below the surface, masked by the surface ice and extreme cold from our orbital instruments. There could even be fumaroles, with gas and vapour escaping to the surface but hidden from our sensors by an ice tower.

All this was just theory until we had observations of methane plumes from Earth. They were puzzling though, as the methane seemed to disappear from the atmosphere so rapidly that it was hard to work out a physical process that could do this. Also these were delicate measurements and needed to be confirmed. But Curiosity seems to have confirmed these observations, though its results continue to be puzzling because they appear and disappear over such short timescales. Perhaps that means they form somewhere close to Curiosity's location. They could also be contamination from Curiosity itself but so far, that seems unlikely.  Hopefully ESA's Trace Gas Orbiter will help clear up some of these mysteries once it starts its science mission in 2017.

So where does the methane come from, if these signals are genuine? Well there are various ideas but all suggest a connection between the surface and the subsurface. The methane plumes on Mars could be results of 

  • Past inorganic processes such as serpentization (reaction of olivine with water at high temperatures) inorganic processes in the atmosphere, volcanoes, or it could be that it was already present on Mars when it formed, locked in clathrates and released
  • Products of past life, again locked in clathrates
  • Present day life using serpentization as an energy source
  •  Present day inorganic processes

We may have spotted methane on Mars. If so this figure from NASA / JPL shows possible sources. One possibility is methane clathrate storage. It's possible that early Mars had large amounts of methane in its atmosphere which helped keep it warm. 

Whether it is the product of present day life or not, these plumes may show a connection between the surface and a habitable region below. So, what happens if Earth life gets into this habitable region after a human crash or landing on Mars? It could be contaminated by methanogens that generate more methane, or methanotrophs that eat them, confusing the scientific study of what caused the plumes. And if there is Mars life down there, the Earth life could confuse the search or compete with them. 

This is not the only way the surface could be connected to the deep subsurface. One of the theories for the warm seasonal flows, or Recurrent Slope Lineae is that they might be the result of water from deep below the surface getting to the surface in regions of geological hot spots. Again this means it could be possible to contaminate the subsurface, maybe even the entire deep subsurface hydrosphere, if it is connected, via the RSL's. 

As Cassie Conley pointed out this could also contaminate subsurface aquifers with microbes that are known to create calcite when exposed to water with CO2 dissolved in it. Later explorers might find subsurface aquifers converted to cement. See Going to Mars Could Mess Up the Hunt for Alien Life (National Geographic).
So far we've been looking at habitats deep below the surface of Mars, though perhaps connected to the surface. But what about habitats on the surface itself? If there are surface habitats, this makes planetary protection even more of an issue.

Habitats for life on the surface of Mars - warm seasonal flows

There are many other seasonal features on Mars but most are caused by dust, wind, or dry ice. The Warm Seasonal Flows or RSL's are the best known, of the ones that may provide habitats for life, indeed there is indirect detection of water flowing there through hydrated salts, those also seem a pretty sure bet for liquid brine but the question there is, is the brine warm enough, for life, and if it is warm enough is it too salty or is it fresh enough for life?

The better known warm seasonal flows. These form on equatorial facing slopes even close to the equator, but only on some of them, extending downwards from bedrock outcrops. The reason why they form on some of those slopes and not on others is not known at present. These examples are on the slopes in Newton crater. High resolution version and techy details here.

It's pretty much confirmed that they involve salty brines in some form flowing beneath the surface. The dark patches are not damp patches but rather some effect on the surface due to the brines flowing beneath. However it's not known yet whether the brines are habitable -they may be either too cold or too salty for life or both. These are very hard to study from orbit because the highest resolution photos we have of them can only be taken during the local afternoon, the worst time to detect the water. That's due to the orbit of the spacecraft taking the photos, which approaches Mars on the sunny side during the local afternoon. For details, see my Why Are Hydrated Salts A Slam Dunk Case For Flowing Water On Mars? And What Next?

Southern hemisphere flow like features

In the case of the Richardson Crater flow like features - especially if they are indeed centimeters thick layers below clear ice - the water will definitely be both warm enough and fresh enough for life. The interfacial liquid layers also seem promising because of the way the models predict them to flow together into a liquid stream of water that then picks up salts on its way out.

g crater, Richardson crater near the south pole. Let me explain why.

First this shows where it is. It is close to the south pole - this is an elevation map and I’ve trimmed it down to the southern hemisphere. You can see Olympus Mons as the obvious large mountain just right of middle, and Hellas Basin as the big depression middle left. Richardson crater is about half way between them and much further south.

Here is a close up - see all those ripples of sand dunes on the crater floor?

Link to this location on Google Mars

Well it’s not the ripples themselves that are of special interest, Mars is covered in many sand dune fields like that planet wide - but little dark spots that form on them which you can see if you look really closely from orbit.

And, would you ever guess? Although it's one of the colder places on Mars, there's a possible habitat for life there in late spring? It is due to the "solid state greenhouse effect" which causes fresh water at 0°C to form below clear ice in Antarctica at a depth of up to a meter, even when surface conditions are bitterly cold.

The Warm Seasonal Flows often hit the news (probable salty brines on sun facing slopes). But for some reason, the flow like features in Richardson crater are only ever mentioned in papers by researchers who specialize in the study of possible habitats for life on Mars. I first learnt about them in the survey of potential habitats on Mars by Nilton Renno, who is an expert in surface conditions on Mars (amongst other things, he now runs the Curiosity weather station on Mars). You can read his survey paper here, Water and Brines on Mars: Current Evidence and Implications for MSL.

The models I want to summarize here are described in his section 3.1.2 Dune Dark Spots and Flow-like Features under the sub heading "South Polar Region". But it's in techy language so let's unpack it and explain what it means.

First, early in the year, you get dry ice geysers - which we can’t image directly, but see the dark patches that form as a result and are pretty sure this is what happens:

Geysers which erupt through thick sheets of dry ice on Mars. Clear dry ice acts as a solid version of the greenhouse effect, to warm layers at the bottom of the sheet. It is also insulating so helps keep the layers warm overnight. Dry ice of course at those pressures can't form a liquid, so it turns to a gas and then explosively erupts as a geyser. At least that's the generally accepted model to explain why dark spots suddenly form on the surface of sheets of dry ice near the poles in early spring on Mars.

So that would be cool enough, to be able to observe them, video them and study them close up. I hope the rover would be equipped with the capability to take real time video. Those are widely known and many scientists would tell you how great it would be to look at them up close.

But most exciting is what happens later in the year, when it is getting too warm for the thick layers of dry ice needed for geysers. You would think that the dark spots that you get in the aftermath of the geysers would just sit there on the surface and gradually fade away ready to repeat the cycle next year. But no. Something very strange happens. Dark fingers being to form and creep down the surface as in this animation. Very quickly too (for Mars).

Flow-like features on Dunes in Richardson Crater, Mars. - detail. This flow moves approximately 39 meters in 26 days between the last two frames in the sequence

BTW it was hard to align these images exactly. I cut them out from the raw data, and aligned them by eye - unlike the RSL's there aren’t any widely shared images of them.

I’ve done my best to register them with each other but I couldn’t figure out a way to do it automatically, indeed, they are taken at slightly different angles also so there is no correct registration that puts each frame entirely in sync with the next one. So that’s why you may see some alignment shifts from one image to the next. It’s the best I can do. The general idea is clear enough.

All the likely models for these features, to date, involve some form of water. Alternatives include a second ejection of material by the dry ice geyser, or dust deposition, but researchers think these are unlikely to produce the observed effects.

That’s not as surprising as you might think. The same thing happens in Antarctica - if you have clear ice, then you get a layer of pure water half a meter below the ice.

The thing is any water on Mars exposed to the surface would evaporate quickly, so quickly that there would be none left. If ice melts there, it turns directly to water vapour because the atmosphere is a laboratory vacuum, it’s so thin.

But - water beneath a layer of transparent ice - that’s a different matter. The water is trapped by the ice so stays liquid. And what’s more, if they model it assuming clear ice like the ice in Antarctica they find that the ice there gets enough heat from the sun in the day to keep it liquid through the night to the next day so the layer can actually grow from one day to the next (ice is an excellent insulator).

Möhlmann's model is pretty clear (abstract here). If Mars has transparent ice like the ice in Antarctica, then it should have layers of liquid fresh water 5 - 10 cm below the surface and a couple of cm in vertical thickness in late spring to summer in this region.

His model doesn't involve salt at all, so the water would be fresh water.

The only question here is whether clear ice forms on Mars in Mars conditions and whether the ice is sufficiently insulating. We can’t tell that really from models, the only way is to go there and find out for ourselves.

Blue wall of an Iceberg on Jökulsárlón, Iceland. On the Earth, Blue ice like this forms as a result of air bubbles squeezed out of glacier ice. This has the right optical and thermal properties to act as a solid state greenhouse, trapping a layer of liquid water that forms 0.1 to 1 meters below the surface. In Möhlmann's model, if ice with similar optical and thermal properties forms on Mars, it could form a layer of liquid water centimeters to decimeters thick, which would form 5 - 10 cm below the surface.

In his model, first the ice forms a translucent layer - then as summer approaches, the solid state greenhouse effect raises the temperature of a layer below the surface to 0°C, so melting it. This is a process familiar on the Earth for instance in Antarctica. On Earth, in similar conditions, the surface ice remains frozen, but a layer of liquid water forms from 0.1 to 1 meters below the surface. It forms preferentially in "blue ice".

On Mars, in his model, the melting layer is 5 to 10 cm below the surface. The liquid water layer starts off millimeters thick in their model, and can develop to be centimeters thick as the season progresses. The effect of the warming is cumulative over successive sols. Once formed, the liquid layer can persist overnight. Subsurface liquid water layers like this can form with surface temperatures as low as -56°C.

Creates potential for flowing fresh liquid water on Mars!

That's for fresh water. The liquid layer below the surface is warmed by the solid state greenhouse effect to 0°C even when the surface temperature is as low as -56°C. The same thing happens in Antarctica, that you get fresh liquid water forming below the surface when the surface temperatures are far too low for liquid water. It's because ice traps heat in much the same way that the CO2 on our atmosphere does, and then the ice and snow is also is very insulating (the reason the Inuit build igloos), so keeps the heat in. That's why the layer forms up to a meter below the surface in Antarctica and why it would form 5 to 10 cm below the surface on Mars, so that the solid state greenhouse effect can warm the subsurface to a much higher temperature than the surface and so that there is enough ice to insulate it to keep it warm.

Inuit village, Ecoengineering, near Frobisher Bay on Baffin Island in the mid-19th century - ice and snow are very insulating. 

In the model, then the ice below the surface is first warmed up in the daytime sunshine, due to a greenhouse effect, the infrared radiation is trapped in the ice in much the same way that carbon dioxide traps heat to keep Earth warm. Then because the ice is so insulating, then the heat is retained overnight, and the water remains liquid to the next day. To start with it would be only millimeters thick but over several days, gets to thicknesses of centimeters.

This should happen on Mars so long as it has ice with similar properties to Antarctic clear ice.

If there is a layer of gravel or stone at just the right depth, the rock absorbs the infrared heat and that can speed up the process. In that case, a liquid layer can form within a single sol, and can evolve over several sols to be as much as several tens of centimeters in thickness. That is a huge amount of liquid water for the Mars surface.

In their model it starts as fresh water, insulated from the surface conditions by the overlaying ice layers. This fresh water of course can't flow across the surface of Mars in the near vacuum conditions, as it would either freeze back to ice, or evaporate into the atmosphere. But the idea is that as it spreads out, it then mixes with any salts also brought up by the geyser to produce salty brines which would then remain liquid at the much lower temperatures on the surface and flow beyond the edges to form the extending dark edges of the flow like features.

Later in the year, pressure can build up and cause formation of mini water geysers which may possibly explain the "white collars" that form around the flow like features towards the end of the season - in their model this is the result of liquid water erupting in mini water geysers and then freezing as white pure water ice

This provides:

  • A way for fresh water to be present on Mars at 0 °C, and to stay liquid under pressure, insulated from the surface conditions.
  • 5 to 10 cm below the surface, trapped by the ice above it
  • Depending on conditions, the liquid layer is at least centimeters in thickness, and could be tens of centimeters in thickness.
  • Initially of fresh water, at around 0°C.

If salt grains are present in the ice, then this gives conditions for brines to form, which would increase the melt volume and the duration of the melting. The brines then flow down the slope and extend the dark patch formed by the debris from the Geyser, so creating the extensions of the flow like features.

They mention a couple of caveats for their model, because the surface conditions on Mars at these locations is unknown. First it requires conditions for bare and optically transparent ice fields on Mars translucent to depths of several centimeters, and it's an open question whether this can happen, but there is nothing to rule it out either. Then, the other open question is whether their assumption of low thermal conductivity of the ice, preventing escape of the heat to the surface, is valid on Mars.

The process works with blue ice on Earth - but we can't say yet what forms the ice actually takes in these Martian conditions. The authors don't go into any detail about this, but ordinary ice can take different forms even in near vacuum conditions. As an example of this, the ice at the poles of the Moon could be "fluffy ice"

"We do not know the physical characteristics of this ice—solid, dense ice, or “fairy castle”—snow-like ice would have similar radar properties. [then they give evidence that suggests fluffy ice is a possibility there] "
(page 13 of Evidence for water ice on the moon: Results for anomalous polar)

That's the main unknown in their model, whether the ice is blue ice like Antarctic ice, or takes some other form.

The ice should be in the same hexagonal structure crystalline phase as ice is on Earth - Mars is close to the triple point in this ice phase diagram

Phase diagram by Cmglee, wikipedia. Ice outside of Earth can be in many different phases. For instance in the outer solar system it is often so cold that it is in the very hard orthorhombic phase, where it behaves more like rock than what we think of as ice. However ice on Mars is likely to be in the Ih phase similar to Earth life. The Mars surface is close to the triple point of solid / liquid / vapour in this diagram.

So, the ice is likely to be of the same type as the blue ice in Antarctica. Not likely to have bubbles of air in it. But it could still take a different forms. The model shows that Mars should have layers of liquid water ten to twenty centimeters below the surface if there are any areas of clear blue ice as in Antarctica.

This solid state greenhouse effect process favours equator facing slopes. Also, somewhat paradoxically, it favours higher latitudes, close to the poles, over lower latitudes, because it needs conditions where surface ice can form on Mars to thicknesses of tens of centimeters. (The examples at Richardson crater are at latitude -72°, longitude 179.4°, so only 18° from the south pole.

There is no in situ data yet for these locations, of course, to test the hypothesis. Though some of the predictions for their model could be confirmed by satellite observations.

Interfacial liquid layers model

Another model for these southern hemisphere features involves ULI water (undercooled liquid water) which forms as a thin layer over surfaces and can melt at well below the usual melting point of ice. In Mohlmann's sandwich model, then the interfacial water layer forms on the surfaces of solar heated grains in the ice, which then flows together down the slope. Calculations of downward flow of water shows that several litres a day of water could be supplied to the seepage flows in this way.

The idea then is that this ULI water would be the water source for liquid brines which then flow down the surface to form the features.

That would still be interesting as you end up having flowing liquid water on Mars, several litres a day what’s more.

Those are the only two models so far. So it does seem very likely that there is liquid water here, and even with the interfacial liquid layers, the water starts off as fresh water beneath the ice, or possibly salty (in either model) if there are salt grains in the ice for the water to pick up.

Northern hemisphere flow like features

Note that there are rather similar looking flow like features in the Northern hemisphere, but these typically form at much colder temperatures for some reason, around -90°C - the two hemispheres on Mars have a very different climate.

Flow like features in the Northern polar dunes . These are thought to form at much lower temperatures. Some of the models for these also involve liquid water but there are other hypotheses as well. This is another animation I made by hand cutting out the images from the raw data, and I was unable to do exact alignment throughout the image, due to the changing angles at which the photos were taken from orbit.

The northern hemisphere has shorter warmer winters (due to Mars’s eccentric orbit), and a lower elevation, but the flow like features there form at times when the surface temperatures are lower than in Richardson crater. There are several different mechanisms for the northern hemisphere flow like features, not all the models for those involve liquid water, and the ones that do involve very cold water. So the Richardson crater ones are the surest bet, seems to me, for a habitable flow like feature.

Other surface and near subsurface habitats for life on Mars

The RSL's and the Richardson flow like features are just two of many habitats suggested on the Mars surface. I like to draw attention to the flow like features particularly, because though the specialists have known about them for many years - his paper is from 2010, it is one of the least publicized, yet in some ways most interesting potential habitats because of the potential for fresh water at 0 °C. As far as I know it is the only surface habitat so far that has the potential to be so warm and also to have fresh water. For some of the others, see

Need for robotic exploration first

All these are places we can explore by telerobotics using increasingly capable robots, also explore using robots controlled from Earth. There is no need to send humans to these places as quickly as possible. It won't help to make us multiplanetary, but it may mean we miss out on discoveries about the origins of life, and other lifeforms. Imagine if you could learn about life on a planet or in the ocean of an icy moon around another star? Even if it was just extraterrestrial microbes or lichens, imagine how exciting that discovery would be? Well Mars, Europa and Enceladus may be like exoplanets and exomoons in our own solar system, they may be as interesting as that. We don't know until we study them close up.

Microbes on Mars, in the more interesting case, would be so different from us, they'd be more like a microbial version of ET than like a tiger. See Will We Meet ET Microbes On Mars? Why We Should Care Deeply About Them - Like Tigers

It's the aspect of our exploration of the solar system that gets most interest of all from the general public I think. And if we did find an early form of life, or something significantly different, it would be the greatest discovery in biology since the discovery of evolution, or perhaps the discovery of the helical nature of DNA, of that order of importance. Who knows what implications it would have, if you think of how much of modern biology comes from those two discoveries.

If we introduce Earth microbes to them, accidentally or intentionally, this may well be irreversible. It's the irreversibility that's the issue here. If it is biologically reversible, not so much of a problem. But if irreversible, that means it would change those places for all future time, not just for us, but for our descendants and all future civilizations that arise in our solar system, they won't be able to make the discoveries they could make by studying these places as they are now, without Earth microbes introduced to them. They also won't be able to transform them in other ways if they decide they wish to introduce a different mix of microbes from the ones we brought there.

I think we just know far too little to make such a decision for all those future generations and civilizations and indeed for ourselves. At present anyway. Future discoveries of course can change this.

What we could learn - some examples

The exobiologists, who hope to fly in situ life detection instruments to Mars some day, design them to be as flexible as possible, to detect not just familiar forms of life. As an example, Chris McKay with his "lego principle" suggests a general way of looking for life not depending on any assumptions that it resembles Earth life. See his What Is Life—and How Do We Search for It in Other Worlds?

What we discover there could include any of:

  • Early life, e.g. tiny RNA world microbes without DNA or proteins. There are many ideas for early life that could perhaps still exist there, though extinct on Earth. These could fill in the huge gap between the organics and cell like structures resembling cells that turn up in laboratory experiments, and the immense complexity of modern life. One idea is an RNA world cell with no proteins, or ribosomes either, instead using RNA sliced into pieces and recombined to make a ribozyme, a tinier distant cousin of the ribosome. This is possible in theory, and some have suggested that present day Earth might have a "shadow biosphere" consisting of RNA world cells, but this has never been confirmed. Maybe we can find RNA world cells on Mars instead? 

    There are many other ideas for early life that could perhaps still exist there, though extinct on Earth, including the so called autopoetic cells that replicate just by producing daughter cells with a similar mix of chemicals when they get large, with no genetic code to regulate the process.
  • Unrelated life, perhaps based on some form of XNA (Xeno Nucleic Acid) instead of DNA. This would be the most amazing discovery of all. It would lift biology into a new dimension, show how life can exist based on completely different principles from DNA based life.

    There are many alternatives to DNA and RNA. RNA and DNA are both particularly fragile, DNA especially and hard to form naturally, need the environment of the cell or special conditions to keep them stable. RNA is more stable when it is very cold for instance, and ribose in its backbone is stabilized by the presence of borates, one of the points in favour of an origin on Mars. Some of the others are more robust and some think we may have started with a PNA world for instance as it is far more robust than RNA and forms more easily.

    Other ideas for early life include TNA world, or a molecule that's a hodgepodge mixing different backbones in the same molecule with non heritable variations in backbone structure (or a whole alphabet soup" of other possible precursors such as HNA, PNA, TNA or GNA - Hextose, Peptide, Therose or Glycol NA).

    The interior of a cell is so complex it's been compared to an entire ecosystem. So life based on different principles could be as revolutionary for biology as discovering a coral reef for your first time, when the only ecosystem you knew about before is the African Savannah. I make this analogy here: "Super Positive" Outcomes For Search For Life In Hidden Extra Terrestrial Oceans Of Europa And Enceladus
  • Life that is based on novel new principles that we haven't thought of yet. For instance, what if other life doesn't use a helix? Suppose for instance that the life used a sheet like two dimensional structure, planar rather than linear, and replication happened by a second layer forming on top of the original sheet?

    Or could it even be a 3D informational polymer? Is there any approach that avoids the need to uncoil to read it? We can do this mechanically through laser scanning, in prototypes for future memory devices, so the idea is not so far fetched as to be totally impossible. 

    This is just fun speculation at present. But suppose that you are an ET biologist and your life uses 2D sheets to replicate - would you not find the idea of a helical structure that has to uncoil and unzip to replicate implausible and unlikely too?
  • Life that has evolved further than Earth life. Mars has had such harsh conditions in the early solar system, alternating ice and more habitable phases. It's also been subject to strong ionizing radiation, extremes of cold, and near vacuum atmosphere. Some think that we have multicellular life on Earth as a result of a snowball Earth phase. If that's true, you could make a case for Mars life to be more highly evolved than Earth life - more complex, more robust cells, with more non redundant nucleotides, and more capabilities than Earth life, maybe even totally novel capabilities never explored here, even if it is just single cell life. 

    Present day Mars probably only has microbes, or perhaps lichens, if it is fair to make a comparison with similarly harsh environments on Earth. But the harsh environment may mean it evolved further on Mars than on Earth. Or could mean it didn't get as far and is an early form of life. It's hard to say in advance which way this would go 
  • Life with a capability Earth life doesn't have, e.g. a new form of photosynthesis

    We have three ways of doing photosynthesis on Earth - broadly speaking. 

    Green sulfur bacteria, which use light to convert sulfides to sulfur, which is then often oxidized to sulfur dioxide
    Normal photosynthesis which splits water to make oxygen, also taking up carbon dioxide in the process. (basic equation 6CO2 + 12 H2O → C6H12O6 + 6O2 + 6 H2O where the oxygen atoms in bold are the same ones on both sides of the equation - see Plants don't convert CO2into O2, and Notes on lamission.edu)
    The photosynthesis of the haloarchaea which works similarly to the receptors at the back of our eyes, based on a "proton pump" which moves hydrogen ions across a membrane out of the cell using bacteriorhodopsin similar to the rhodopsin in our eyes, with no byproducts such as sulfur or oxygen, just creates energy directly from the proton gradient.

    ET microbes might well use some fourth form of photosynthesis that has never been explored on Earth.
  • Life similar to Earth life in most respects, would raise many questions. How has it evolved in such a different environment, since last transfer from Earth, surely at least tens of millions of years ago. How did it get there? We can test the theory of panspermia, find out in practice how easy it is for life to be transferred to another planet.
  • Uninhabited habitats - no life but with organics, and all the ingredients for life. This may seem boring, but it would tell us a lot about how hard it is for it to evolve on a planet, and about the paths it follows on the way to life. If not life itself, there has to be some complex organic chemistry going on, and cell like structures surely form, as that happens even in short term laboratory experiments. So how far did it get and what exactly happens on a world similar to Earth in many ways (especially in the early solar system), but without life?

    Also, on Earth it's impossible to study uninhabited habitats, except for a very short time after a volcanic eruption. Life appears rapidly on any uninhabited habitat here. On Mars, we might have the opportunity to study uninhabited habitats on a planet that hasn't been inhabited for billions of years. This could help us to understand exoplanets and the origin of life and maybe find out that life is harder to evolve than we thought. It can also help to disentangle effects of life and non life processes on Earth.
  • Some major unexpected discovery that nobody currently is likely to predict.

All possibilities here are of exceptional interest for biology. If there are habitats for life at all on Mars, whether inhabited or uninhabited, then biologists world wide will want to study them as they are now, and the results in the best case could be revolutionary for biology.

Uninhabited habitats

This is something that Charles Cockell has explored in a series of articles. His latest is Trajectories of Martian Habitability.

One thing that greatly complicates the search for life on Mars is the possibility of uninhabited habitats. On Earth, if you find a habitat with all the conditions that life needs to survive, you expect to find life also. The only uninhabited habitats are new ones, such as recently cooled lava flows, or artificially created habitats such as petri dishes, or occasionally in very extreme conditions such as patches in the McMurdo valleys (as mentioned in the quote above)..

On Mars though some or all of the present day habitats may well be uninhabited. Perhaps life never evolved, or it evolved but became extinct, or it just takes a long time for life to colonize a new habitat in the harsh conditions on the surface of Mars. Perhaps it takes hundreds of thousands of years or millions of years for life to colonize a newly formed habitat on Mars.

Uninhabitable liquid water on Mars

You also have the complication that water on Mars might not be habitable at all. Almost all places on Earth where you find water, or even water vapour from the atmosphere, you also find life, including salt lakes, concentrated sulfuric acid, permafrost, and places like the Atacama deserts and the McMurdo dry valleys. But you could get liquid water on Mars in conditions even more inhospitable for life than any of these.

A nice example of an uninhabitable water rich environment on Earth is honey. Though it's got plenty of moisture, the water activity level is too low and it also has anti-microbial properties. No life can colonize it; though spores can survive there in dormant form. Apart from that, about the only place where we have uninhabitable liquid water on Earth may be the extremely salty Don Juan pond in Antarctica - and even there there is some doubt about whether it is completely uninhabited.

Some regions of Mars could have liquid water, but not be available for life to use. Reasons could include, too much by way of salts (including chlorates, and sulfates), too much acid, or lacking essential trace elements and nitrogen. Conditions were better in the past, even the recent times when the Mars atmosphere was a bit thicker on occasion. But It's a special challenge for present day life on Mars; because over much of the surface, ice sublimes directly to water vapour or is close to its boiling point right away. So only salty brines could be stable in habitats exposed to the surface,- and these may be too salty for life to use. There's a narrow habitability zone between water that is salty enough to remain liquid and water that is so salty that life can make no use of it. There may be many uninhabitable patches of liquid brines on Mars for each habitable patch.

Early life not so versatile as present day life

You might think that uninhabited habitats would be rare in the early Noachian, so long as life evolved on Mars at all. It had oceans covering much of the planet, and organics delivered from comets and meteorites. Unless its water was extraordinarily acid, alkaline, or salty, then surely it must have had life almost anywhere?

However, if you start thinking in terms of early life, even before the evolution of the first archaea on Earth, the early Noachian may not seem so hospitable after all. For one thing, it might have taken a while before life developed hardy resting states and microbial spores. Without that, it would be confined only to habitable regions and couldn't spread from one to another easily.

Then, nobody knows when photosynthesis first evolved on the Earth. Perhaps it was present almost from the beginning, but maybe it developed rather later. In an early Mars without photosynthesis, life would be confined to places where it could take advantage of chemical energy.

Perhaps it lived in hydrothermal vents, but there are many other ideas for abiogenesis (origins of life). Some think that life could have evolved in icy conditions, where melting and refreezing ice concentrates organics (eutectic freezing). Or it might have evolved on a clay substrate in a hydrogel which experimenters found can be used as a "cell free" medium for protein production from DNA, amino acids, enzymes and some components of cellular machinery. Or perhaps it evolved on pumice rafts.

Pumice and ash floating on Lake Nahuel Huapi, Bariloche, Argentina

One theory of the origin of life (amongst many) is that it might have started in pumice rafts like these. If this is what actually happened on Mars, and if it took it some millions of years to evolve to the stage where it could colonize harsher conditions, then we might have to search for pumice rafts to find evidence of the earliest life on Mars.

This is one out of dozens of suggestions for the origins of life. The hydrothermal vent hypothesis is perhaps the most popular but there are many others.

Another theory is that it originally evolved kilometers deep underground, rather than on the surface. Wherever life started on Mars, the big question then is - how long did it take to spread to other habitats of the same type, and how long did it take to diversify to other habitats?

Early pre-archaea type life on Mars could be extremely localised

We might, for instance, find the primitive pre-archaean cells only in the hydrothermal vents in the early Noachian period. Other apparently equally habitable areas could be devoid of life. Also, it would be hard for such primitive life to transfer from one vent to another, to start with at least. So, even the hydrothermal vents of the Noachian period might not all have life in them. Or different vents might have life, or protobionts, that developed independently through different pathways. There are exposed remains of hydrothermal vents on Mars, so is that where we need to go? And which one?

The first cells also might not have reproduced like modern cells with their complex transcription methods and error correction. If they could reproduce in the modern sense, yet it might be with many errors and changes, and not reproduced as exactly as present day cells. Early life might have got going in fits and starts, with the first cells easily going extinct. Perhaps remains of one attempt at life provided the raw materials for the next attempt until finally it succeeded long term. And protobionts might not have had any informational coding molecules at all.

The main problem is we have no timescale for this. Of course life must start somewhere, or several places at around the same time perhaps; but how long does it take for it to develop a robust reproduction system, to develop the ability to colonize many different habitats, and to spread from these starting points to cover a planet?

It might have needed millions or hundreds of millions of years in stable conditions such as hydrothermal vents for primitive pre-archaea to evolve to the complexity of a modern cell. Or maybe all this is possible within a million years or less. Nobody knows. We can't create these conditions in a laboratory and have no evidence at all from early Earth.

Alternative of rapid development of archaea or life of similar robustness and complexity

So, the other way around, life might even have evolved more rapidly on Mars than it did on Earth. After all there was no moon creating impact, and Mars doesn't seem to have had global magma oceans even in the early Noachian. The impacts from the Late Heavy Bombardment on Mars were probably survivable by life. Also Mars was a very different planet with shallow oceans and quite possibly freezing conditions early on (which may be a benefit if you take the view that eutectic freezing helped to concentrate organics and encouraged evolution of life).

So, at the other extreme, life on Mars might have evolved far more rapidly, all the way to photosynthetic life by the beginning of the Noachian period. Who knows, perhaps it evolved even to multicellular life.

One recent paper by some researchers in Oxford, as a result of looking at differences between Mars meteorites and the composition of surface rocks measured by Spirit rover, suggests that Mars might have had an oxygen rich atmosphere in the Noachian period 4000 years ago.

So there are many possibilities for early Mars. It might have been totally uninhabited. It might be inhabited but only in special locations, such as hydrothermal vents, or rock pools on ocean margins, or deep underground. Or it might be inhabited almost everywhere, so that you can find traces of early martian life in any habitat with conditions suitable for modern life, so long as it was buried in conditions suitable for preservation of the organics.

There is no way to decide between these various scenarios on theoretical grounds. The only thing we can do is to search, everywhere we can think of, and see if we can find it. We might finally find the first traces of early life on Mars in some unexpected place nobody predicted.

Idea of returning samples from Mars to Earth

When Curiosity's successor and the ExoMars rover land on Mars around 2021, we will see two different approaches to the search for life on the planet side by side. NASA's mission is the first stage of a sample return program. The ESAs ExoMars rover (in partnership with Russia) will explore Mars in situ for biosignatures as well as drill two meters below the surface. Which is the best approach? 

A sample return would be great for geology. But would it help with the search for life on Mars? Or is it more of a technology demo for this?

NASA's decision was based on the last planetary science decadal survey in 2012, for the decade 2013 to 2022. In this survey, NASA asks for input from panels of space scientists. 

Sample return with SpaceX's Red DragonNASA do one high cost "flagship mission" in each decade.  The committees chose a sample return mission (over the Jupiter Europa Ocean mission), but with the funding available, they could only pay for the first half, sample caching on Mars. They left return of those samples to Earth as a decision for the next decade. So essentially, it's a double decade flagship mission. 

This makes it one of the most expensive decisions NASA has committed to in the field of planetary sciences in recent years. It would return less than a kilogram of material at a cost of millions of dollars per gram.

MSR ascent moduleNASA are just first off the block. Other countries that may do a sample return in the near future include Russia, China, and indeed the ESA themselves who have explored the idea for many years.

Surely someone needs to do a comparison study before such expensive decisions? 

It turns out that someone did, in a white paper submitted to the decadal survey itself. Surprisingly given the outcome of the survey, and the enthusiasm of many space scientists for the idea, this study comes out firmly in favour of in situ exploration and against a sample return, for astrobiology.

A study like this would normally be followed up by more detailed studies, so it has to be treated as preliminary. But it's all we have at present. Why did these astrobiologists come out so strongly against the idea of a sample return? When they, of all scientists, are keenest to find out about Mars life, if it exists? And what are the implications for NASA's plans?

Well it's because they were early life enthusiasts rather than fossil optimist, I've covered the paper already above in Follow the nitrogen, dig deep and look for biosignatures. So they expect Mars past life to be hard to find, as hard as the search for past life in ALH84001. With that background and the complex geology of Mars, it's not at all clear that we can hope to find evidence of past life on Mars easily, or at all, by sample return missions unless we already know it is there, and where to look..

Impossibility of sampling everything

This region of the Mawrth Vallis area of Mars gives some idea of the complexity of the situation on Mars.

Imagine trying to study this region by returning samples to Earth for analysis? And now, imagine that you also have to drill below the surface to find samples less affected by ionizing radiation?

Close up image of a region of stratified clays in the Mawrth Vallis region of Mars

With current ideas, the sample would only return small quantities, probably less than a kilogram in total. So there is no way we can do a complete survey of any moderately complex region of Mars and return samples from all the interesting points in the region.

An in situ search on the surface is not restricted in any way. We can continue studying new samples indefinitely. We can also home in on regions of interest.

If an in situ study finds that a particular band of rocks, or type of rock, for instance, is of especial interest - then the in situ rover can then focus the search on other rocks of that type. Perhaps it finds a chiral signature, or it finds amino acids or other biologically interesting molecules. Then it can focus the search on that layer or those rocks, and follow the signal.

Or it can drill into the layer to get deeper samples and so on. It can make decisions about where to go next based on the analyses already done. But if you have to return the rocks to Earth to search for biosignatures, this is impossible.

Tissint meteorite - a great example of what we might get in a sample return from Mars

Another example of a fascinating Mars meteorite is the Tissint meteorite, which was in the news recently. It's a witnessed fall, so one of the least contaminated of all the Mars meteorites, only been sitting around for a few days before it was collected. Again, for various reasons, some scientists see this as good evidence of early life on Mars.

This also is proving as controversial as ALH84001. See Meteorite May Contain Proof of Life on Mars, Researchers Say and Experts Cast Doubt on Meteorite Study's Claims of Martian Life

Here you can see a fragment of this meteorite from London's Natural History Museum, discussed by Caroline Smith, their meteorite expert.

It would be wonderful to have a few more samples like these two meteorites. And especially so, it would be great to have the context, the exact location they come from on Mars.

However, is it worth the price tag of millions of dollars per gram, to get more samples like this, even ones that are brought straight to Earth from Mars in a spacecraft? How much will this help with the study of exobiology and the possibility of life on Mars? You have to bear in mind the impact this has on other missions, which won't be flown because the funding is used instead for a sample return.

This was the question the exobiologists addressed in their study. And they came down strongly in favour of in situ exploration at this stage of our exploration of Mars.

"Two strategies have been suggested for seeking signs of life on Mars: The aggressive robotic pursuit of biosignatures with increasingly sophisticated instrumentation vs. the return of samples to Earth (MSR). While the former strategy, typified by the Mars Science Laboratory (MSL), has proven to be painfully expensive, the latter is likely to cripple all other activities within the Mars program, adversely impact the entire Planetary Science program, and discourage young researchers from entering the field."

"In this White Paper we argue that it is not yet time to start down the MSR path. We have by no means exhausted our quiver of tools, and we do not yet know enough to intelligently select samples for possible return. In the best possible scenario, advanced instrumentation would identify biomarkers and define for us the nature of potential sample to be returned. In the worst scenario, we would mortgage the exploration program to return an arbitrary sample that proves to be as ambiguous with respect to the search for life as ALH84001."

Instead of a sample return at this stage, they recommend more thorough in situ searches, and increased mobility, to look at the many possible habitable environments on Mars. They also recommend drilling to depth, and searching for biosignatures. 

The main difference in the perspective of the astrobiologists, and the geologists, is in the timing. They recommend a sample return at a later stage in exploration, once we have explored Mars more thoroughly and definitely identified biomarkers on Mars.

Alternatively, if we never find biomarkers on Mars, we could return samples after we have exhausted all the in situ technologies available to explore for the biomarkers on Mars itself directly.

Decadal summing up doesn't discuss this issue

The decadal survey does list their paper amongst the submitted white papers at the end of the report. But it is not cited in the body of this report or discussed. Nor is it mentioned in their final presentation (which is available as a video online).

This is what the decadal survey says:

The Mars community, in their inputs to the decadal survey, was emphatic in their view that a sample return mission is the logical next step in Mars exploration. Mars science has reached a level of sophistication that fundamental advances in addressing the important questions above will only come from analysis of returned samples.

The site will be selected on the basis of compelling evidence in the orbital data for aqueous processes and a geologic context for the environment (e.g., fluvial, lacustrine, or hydrothermal). The sample collection rover must have the necessary mobility and in situ capability to collect a diverse suite of samples based on stratigraphy, mineralogy, composition, and texture. Some biosignature detection, such as a first-order identification of carbon compounds, should be included, but it does not need to be highly sophisticated, because the samples will be studied in detail on Earth.

Vision and Voyages for Planetary Science in the Decade 2013-2022

As we've seen, the white paper is hardly "emphatic in their view that a sample return mission is the logical next step in Mars exploration.", indeed the opposite of the decadal survey's conclusion would be a somewhat more accurate summary.

Here I pick out some of the things they say in the summing up, and compare them with the statements in Bada et al's paper.

  • Summing up: "fundamental advances in addressing the important questions above will only come from analysis of returned samples"
  • Bada paper: "We have by no means exhausted our quiver of tools, and we do not yet know enough to intelligently select samples for return


  • Summing up: "Some biosignature detection, such as a first-order identification of carbon compounds, should be included, but it does not need to be highly sophisticated, because the samples will be studied in detail on Earth."
  • Bada paper: "We argue here that when in situ methods have definitively identified biomarkers, or when all reasonable in situ technologies have been exhausted, it will be time for MSR. We are not yet at that crossroad."

How did this happen? Given that the main objective of the sample return is to look for life, you'd expect the views of astrobiologists to have top priority, so why weren't they mentioned at all? At the least, you'd think it would trigger an in depth study of some sort, to follow up their research in more detail.

Will the sample return happen this time?

It's a two decade project, and given the expense and technical challenges, it may not happen. Many earlier plans for a sample return never came to anything.

1978 proposal for orbital Anteus receiving facilities for Mars Sample Return
Antaeus Orbiting Quarantine Facility (1978)

The idea of a Mars Sample Receiving laboratory was first studied in 1978. The idea then was for an orbiting quarantine facility called Anteus to receive the samples. 

Other proposals were explored in the 1980s, including direct entry of a sample container to the Earth's atmosphere, recovery by the space shuttle, recovery to the space station, recovery to a dedicated Antaeus space station, and several intermediate proposals. Mars Sample Recovery&Quarantine (1985)

Perhaps this time it will happen however? If so, what can we do to help make it a success, and a valuable part of our space program? Can we do anything to reduce the huge cost? And can it be done safely, given the issues for back contamination of the Earth? At reasonable cost?

Rhythms from Martian sands - what if Viking detected life?

There is one scenario that could mean that we return life from Mars right away, maybe even in the first samples from the planet. What if there is life there already in the sand dunes, and Viking detected it? Gilbert Levin has been saying this for decades, and recently some other scientists have found new evidence that may support him. See Rhythms From Martian Sands - What Did Our Viking Landers Find in 1976? Astonishingly, We Don't Know

If that is correct - then since Viking didn't land anywhere special on Mars, it probably means that life is present in low concentrations almost everywhere.

In this scenario ExoMars will probably detect biosignatures of life quickly, maybe right away. Its instruments are sensitive enough to detect life even in the Atacama desert (where levels of organics are too low for Curiosity and Viking to detect anything). In this scenario, ExoMars finds biosignatures in trace quantities almost everywhere it looks, in the Martian sand dunes. Then Curiosity's successor would be expected to return life in the sample.

But of course it doesn't go the other way. If the sample return doesn't contain life, it doesn't even conclusively prove that Gilbert Levin's interpretation of the Viking data is incorrect (perhaps Curiosity's successor is unlucky or both Viking landers were very lucky). It certainly doesn't mean that there is no life on Mars, or even, no life in the equatorial regions!

Unless you have a lot more context to interpret the result, all you can deduce from a sample return with no life in it is that there are places on Mars where life is not present. Which would be hardly a huge surprise.

Mars sample return as a geology mission and a technology demo

The decadal survey summing up motivates the Mars sample return using examples of previous returns of comet and interplanetary dust, and moon samples.

Tracks of particles from comets collected in the stardust aerogel, first sample return of a comet to Earth

These undoubtedly were hugely valuable in advancing our understanding. But those are all astrogeological missions, and their value was geological.

Geological specimens don't deteriorate in the same way as organics. There is no problem of racemization, or of lifeforms eating them, and usually no problem of them being washed out by flooding.

They are also easier to find. They are also relatively easy to identify. The sample return from Mars may well be of great value for geology. Nobody controverts that.

Astrobiological motivation

The big difference is that a Mars sample return is motivated mainly by its value for exobiology. Geologists would love to get hold of a sample from Mars. However, it's hard to motivate a multi-billion dollar mission to return a kilogram or so of samples from Mars for the geology only. Especially since we are making great strides in understanding the geology of Mars robotically and have many meteorites from Mars already.

If the motivation is geological, you listen to the planetary geologists. But if the motivation is astrobiological - surely you need to listen to the astrobiologists? Methods that work for astrogeology may not work so well for astrobiology.

Why did the decadal survey choose a sample return?

To return to our earlier question, why did the decadal survey choose a sample return mission over in situ exploration? Why didn't they listen to the astrobiologists?

I don't know the answer to that, since they don't discuss the Bada paper at all as far as I can see (do correct me if you know of anything they say on this subject, anyone, or you have any more information on the background to this). But I can offer a few thoughts that might be relevant.

NASA, of all the space agencies, is the one most focused on the aim of an eventual human landing on Mars. So could it be connected with that?

"Safe on Mars" - could a sample return tell us if mars is safe for astronauts?

This is just a guess, but I wondered if it is possible that they were motivated partly by the Safe on Mars report in 2002 (which is cited by the decadal survey). This recommended a sample return from Mars to check to see if there are any biological hazards for humans on the surface.

This is a 2010 animation showing how a sample return from Mars might have been done with 2010 era technology (they show it returned to the space shuttle).

If so, it's interesting to note that Safe on Mars recommended a sample return only because at the time they wrote the report, there were no instruments sensitive enough to do a good search in situ, in their view. They say:

As stated above, there are currently no measurement techniques or capabilities available for such in situ testing. If such capabilities were to become available, one advantage is that the experiment would not be limited by the small amount of material that a Mars sample return mission would provide. What is more, with the use of rovers, an in situ experiment could be conducted over a wide range of locations.
(Page 41 of Safe on Mars)

So, actually, when you read it in detail, it's a similar recommendation to the one by the astrobiologists.

Well, now, these capabilities are available. Many instruments that were huge laboratory filling machines even as recently as this report in 2002, with no chance at all of sending them to Mars - they have now been miniaturized and a fair number also tested in space simulation conditions, and could easily be sent to Mars.

These include DNA sequencers, electron microscopes, ultra sensitive biosignature detectors able to detect a single amino acid in a sample, and updated versions of the Viking Labeled release using chirality to eliminate false positives. Our instruments also include the exquisitely sensitive electrophoresis "lab on a chip" methods mentioned by Bada et al. Another new idea is the Solid3 approach of using polyclonal antibodies - which can detect, not just the organics you find in animal bodies, but a wide range of organics, again with exquisite sensitivity, and a "lab on a chip".

A sample return can only tells us that there are some rocks on Mars which are safe for humans

The geology of Mars is much more varied than realized in 2002 when that report was written, and conditions for habitability even more so. We have ideas now for potential habitats for life even in equatorial regions such as the advancing sand dunes bioreactor and the warm seasonal flows. These habitats could depend on things such as small local variations in the concentrations of various salts in the soil. Also there are ideas for ways that life could survive (perhaps just below the surface) using the night time humidity with no water at all.

It doesn't seem likely that a few samples returned from the surface even of a large plain of sand dunes, for instance, would be able to confirm or deny the advancing sand dunes bioreactor hypothesis. There might be only a few sand dunes with the right mixtures of salts to give conditions for life in the entire plain. Or life might have colonized some rocks and not others, just through chance (as happens in deserts on the Earth).

So, we can't hope to deduce that much from a small sample return about present day life on Mars. At least - not without a lot more context and understanding than we are likely to have by then.

If it has no life in it, all you can say from a selection of samples like this is that there are some rocks and sand dunes on Mars that have organics, but don't have life in them. That's no great surprise. 

And if there is life in the sample - again - it doesn't tell us that much about the range of possible lifeforms on Mars. Mars may well have more than one species of life - so would they all be present in these first samples returned from Mars? If we find a cyanobacteria for instance - does that mean that the only life on Mars is cyanobacteria? Not likely we could conclude that from just a few samples returned from Mars.

In conclusion, given what we now know about the variety of conditions on Mars and the varied possibilities for habitats there - it doesn't seem likely that a sample return from Mars at this stage would settle anything about safety of surface conditions for astronauts.

How can we protect Earth during a sample return mission?

A sample return is not only an expensive mission, it also raises unprecedented issues of planetary protection for the Earth, and especially so if the sample is returned at such an early stage, when the planners of the mission can have no idea what is in the sample of biological interest.

If NASA does go ahead with the second half of their proposal, and they do a sample return, this is something that Carl Sagan and others have argued is something we should only do with great caution.

I have two new suggestions here that could, just possibly, help resolve this.

First, though, for those of you who are new to this, let's just summarize the way that it would be done according current ideas.

Sample return with unsterilized sample

If the sample is unsterilized, we have to take precautions to protect the Earth. That is the conclusion of all the studies into the back contamination risks of a Mars sample return to date.

Easy part, sample return to surface in container

The easy part is to return a sample to the Earth surface. That's pretty much worked out. The idea is that you have to break the "chain of contact" with Mars. Make sure nothing that has contacted the Mars surface or contacted anything else that contacted the Mars surface is exposed to Earth environment.

The easiest way to do that is to use nesting capsules. The Mars sample is placed inside a larger capsule in Mars orbit. On return to the Earth system, you could indeed put it inside an even larger capsule enclosing both. Make sure that there is no way those capsules can be broken even in event of a crash landing on Earth.

The main issues there are - that a micrometeorite could pierce the capsule - and human error, some mistake in design of the capsule that is never picked up all the way through the design process - and a bad re-entry that burns up the capsule so that the interior is exposed. But a carefully designed mission could deal with all those - those are addressable issues.

Hard part - what do you do next once you have a sample on the Earth?

The hard part is, what do you do when it returns to Earth? If you just wanted to keep the sample in its container for ever, simple, bury it deep below the ground. Maybe enclose it in synthetic rock. Or simpler still just sterilize it completely with ionizing radiation and all is safe and dandy.

But of course that's not what we want to do. We need to study it, in a laboratory, cut bits out of the sample, and move those fragments around and look at them in many different machines. Eventually to send those samples to other laboratories around the world. You’d think this was easy, but it turns out to be surprisingly complex and difficult. Back in the 1990s the general idea was that we can just return samples to a glove box facility in a biohazard 4 laboratory. Idea was - that since we know how to contain hazards such as the Ebola virus etc, surely there would be no problem containing a sample from Mars. Just use the same techniques we already use in biohazard laboratories.

After a series of studies, however, it was realized that it's not as simple as it seemed at first. The precautions needed got more and more complex. The most recent studies require a facility costing perhaps half a billion dollars or more, with capabilities never tested before. One problem is that it is easy to contain a known pathogen, say smallpox, or anthrax, or the Ebola virus etc. Because you know that it needs an animal host (maybe a human host), and know what kills it. But what can you do when you don’t know what is in the sample, what its capabilities are, what size it is, or even what biochemistry it has? And if it possibly doesn’t use DNA? And perhaps it is a spore in resting state, that is highly resistant to ionizing radiation, to oxidising agents like hydrogen peroxide, and other chemicals, able to survive vacuum conditions, etc etc - all of which are very likely to be the case for Mars life? And could be tiny far smaller than any Earth life?

The smallest size for early cells if they don't contain all the machinery of modern life, is generally estimated as about 40 nm. Successive studies by the National Research Council (NRC) in the USA (two studies) then the European Science Foundation (ESF) (one study) gradually lead to more and more stringent requirements. First came the reduction to 200 nm by the NRC after discovery of the ultramicrobacteria Then, that was reduced to 10 nm by the ESF. as a result of discovery of how readily archaea can share their DNA through the tiny Gene Transfer Agents (GTAs)

Credit: Zina Deretsky, National Science Foundation

The red colouration of this pea aphid comes from a unique ability to generate carotenoids itself. It got this ability through horizontal gene transfer from a fungi.

Archaea can also transfer genes between phyla that are as different from each other as fungi are different from aphids. It is an ancient mechanism and so may also be able to transfer genes from life that had last common ancestor with us in the early solar system.

In one experiment 47% of the microbes (in many phyla) in a sample of sea water left overnight with a GTA conferring antibiotic resistance had taken it up by the next day

So if the life is at all related to Earth life, you have the possibility of this exchange of DNA bringing new capabilities to Earth microbes from space. Even if the microbes themselves don’t survive.

Another thing that makes the design more complex is the need not just to contain the sample (which is usually done by a positive air pressure from outside) but also to protect it from outside organics (which needs a positive air pressure from inside). You end up with some kind of a double walled facility and they cite this as one of the main reasons why you have to have a new design of building, never tested before.

This is one of the designs they came up with in 2008, with telerobotics.

The LAS sample receiving facility uses a fully robotic workforce, including robotic arms that manipulate samples within interconnected biosafety cabinets. Carrier robots would transport the samples around the facility. Credit: NASA/LAS

This is for just a less than 1 kg of samples returned most likely, yet you have to build something like this. And even then, it might not be sufficient. Every Mars sample return study to date says at the end that their conclusions have to be reviewed continually, based on new research. For the next study, whenever it is - well there is much active research at present into into a semi synthetic minimal living cell or an artificial minimal cell. Does the 40 nm size limit still apply based on the recent research? In the Programmable Artificial Cell Evolution project, the smallest artificial minimal cells were as small as 103 atoms, based on PNA instead of DNA, making it possible to simulate the whole cell as a quantum mechanical system in a computer. These “cells” were just a few nanometers across.

Also there's much more work been done on possible XNA based life, and I would expect that to feature more in a new study than in previous ones. And none of the studies to date address issues of human error, accidents, terrorism, a crash during transport of the sample to the facility, a plane crashing into the facility etc. The studies done to date mention these issues, but only to say that these issues were not part of their remit.

And then after all this work - we might find that the sample receiving facility wasn't even needed. The samples returned might be completely harmless. It seems a back to front way of proceeding to me. Wouldn't it be better to first characterize the sample before we return it? Then design the facility around the samples once we know what they are?

For more about this see my Need For Caution For An Early Mars Sample Return - Opinion Piece

Legal complexities

Margaret Race (of the SETI institute) covered these in an excellent paper. There’s far more to it than you’d think. Back in days of Apollo, the quarantine rules for the Apollo 11 return were only published on the day that they launched to the Moon, giving no opportunity at all for comment or peer review. That would simply not be permitted today. Also the Apollo regulations have lapsed.

Also, there are many domestic and international regulations to be negotiated and new laws to be passed. She considered the whole process likely to take ten years or more, and it can also potentially involve the domestic laws of nations that are not receiving the sample, because the potential effect of the worst case scenario could impact on all nations. It would be a process that would be carried out in an open fashion with public debate. See Planetary Protection, Legal Ambiguity, and the Decision Making Process for Mars Sample Return

Natural contamination standard - great for asteroids and comets but doesn't work for Mars

There is one argument, simliar to Zubrin's meteorites exchange argument, which is used in planetary protection calculations. That's the natural contamination standard. If you can prove that what you are doing is equivalent to what happens naturally, then the mission is not a biological issue. That's used for sample returns from comets and asteroids to Earth. Since fragments of comets and asteroids hit Earth all the time, then it's not adding to the hazard, whatever there might be. If there is any life on comets or asteroids, which is not ruled out, then we've evolved to be able to cope with its influx into our atmosphere, so there's no problem returning those samples.

The problem with Mars is that sending humans to Mars or returning samples from Mars to Earth is not like the processes that happen naturally. The natural contamination standard would involve simulating somehow the equivalent of 100 years of interplanetary cosmic radiation, and vacuum and the cold of space. And even then, those are events that happen only every 100 million years or so. While in the reverse direction from Mars to Earth, it might not have happened at all for billions of years, depending on whether any meteorite that hit Mars not only hit a habitat for life there, but also sent life into orbit - given that the material that goes into orbit comes from a distance of a few meters below the surface, and the surface habitats that may have life consist of dust, clays, and ice which would most likely just be scattered back into the atmosphere..

We'll only be able to fill in the gaps in this picture once we have life detection from Mars, if there is life there. From the evidence so far, we might well find habitats on Mars without Earth life in it, habitats that Earth life could inhabit. There's another way also that Earth life might not be in those habitats. That is if they are very rare on Mars and form for a few centuries then go away. Maybe the Earth life just doesn't get there in time with a few spores spread in the dust storms before the habitat disappears again. That happens on Earth also in newly formed lava flows but it only takes a few weeks for Earth life to colonize them. On Mars maybe it takes centuries or millennia. It might be in some of the habitats and not in others. It might occupy them on Mars for some time, even perhaps occasionally for millions of years, then go extinct.

So anyway - Zubrin and a couple of exobiologists have put forward a thesis according to which they think that habitats on Mars will have exactly the same lifeforms that the sam habitats have on Earth. But they don't go into details about how it would happen. It's largely "hand waving" arguments, and it's by no means proven and is rather controversial. I think many exobiologists would be very surprised if that's what they found. And would be bound to be some differences which you'd want to explore and understand, if he was right, to learn which lifeforms got to Mars, how they got there, and how they survived when they got there, what was the first lifeform to get there, and how they evolved and changed after spending tens of millions of years, perhaps billions of years, in Mars conditions.

But could also be that it just never happened. Or that there's a mix of Earth and native Mars life that gets on fine on Mars but won't work any more after you introduce more Earth species. Or perhaps Zubrin is right and somehow all the Earth lifeforms that could survive in those habitats are already there. If so that would be an extraordinary event that you'd want to understand well before introducing more present day Earth life to Mars. Or there might be habitats but no life, as Charles Cockell talks about, and again you'd want to understand that well too. It could give us insights into exoplanets that don't have life, and into the role of life in geological processes on Earth as a "control" and tell us something about how far complex chemistry can get on its way to life on a planet without life.

One way or another, I think it is just far too soon to say that it is okay to introduce Earth life to Mars.

For more on all this see my:

Does Earth Share Microbes With Mars Via Meteorites - Or Are They Interestingly Different For Life?
Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisited 
No Simple Genetic Test To Separate Earth From Mars Life - Zubrin's Argument Examined

Why quarantine won't protect Earth or humans sent to Mars - if Mars life exists

Mars life could also be hazardous for Earth (this question about whether microbes from one planet can harm life on another goes both ways). If you haven't come across the scientific papers and workshops and studies on this issue before, chances are you're first thought will be of the "Andromeda strain" or some other science fiction scenario. In that case it's viruses from outer space. But viruses aren't a likely problem for humans going to Mars, because they have to be adapted to their host. Any life on Mars has never encountered humans before so can't be adapted to us.

There are many other ways though that Mars life could be hazardous to humans and also to the biosphere of the Earth.

  • Gene transfer agents. These are much smaller than viruses, and they can transfer small fragments of DNA from one species to another to give them new capabilities. It's an ancient mechanism, and works between distantly related species. GTA's can transfer capabilities between species as unrelated as fungi and aphids (example of a GTA that gave an aphid the capability to create carotene, from a fungus). Also it works very quickly between microbes in sea water, if the GTA's ever got into the sea. In one experiment a GTA conveyed antibiotic resistance on 47% of the microbes in sea water, all types, just the microbes you have in sea water naturally, after they left them exposed to the GTA's overnight. This is relevant if Mars life is distantly related to Earth life. Even if the life got transferred from Earth to Mars or Mars to Earth billions of years ago, it could still exchange capabilities with Earth microbes readily using GTA's 
  • Life not based on DNA which has chemical signatures that Earth based life is not designed to respond to. Our defenses would only respond to the trauma, not to the cause of it. This is a point made by Joshua Lederberg, Nobel prize winning microbial geneticist, in Parasites Face a Perpetual Dilemma and also in Exobiology: Approaches to
    Life beyond the Earth 
    and a nice quote here: 

    "If Martian microorganisms ever make it here, will they be totally mystified and defeated by terrestrial metabolism, perhaps even before they challenge immune defenses? Or will they have a field day in light of our own total naivete in dealing with their “aggressins”?
     in his "Paradoxes of the Host-Parasite Relationship" (he also gives an interesting analogy there with symbiosis with mitochondria)

    In the worst case, of total naivete on the part of Earth microbes, lifeforms like this could live on our bodies, in our guts, and produce chemicals that are poisonous to us or take the place of microbes that we need to survive. Or just eat us. And our defenses might not respond. 
  • Life from Mars could harm us in many other ways, not just directly as diseases of humans. If the life from Mars has a major effect on microbes that we depend on (like the algae in the sea) or on the plants we depend on for food, wood and so on, or on the animals, it could be just as disastrous for the environments on the Earth. As an example, cyanobacteria produce toxins that kill cows. There's no evolutionary advantage in this as far as we know, the cyanobacteria can't eat the cows and it's unlikely to be a measure to deter predation by cows. It's just a case of toxins that are effective over a large evolutionary distance. See Alien Infection (Astrobiology magazine, 2008). 

    For another example, cyanobacteria produce BMAA which is implicated in Alzheimer's. This is a chemical that resembles L-serine and can be misincorporated in its place and cause folding disorders in proteins, amongst other effects. Again there is no advantage to the cyanobacteria to cause Alzheimer's. in humans. And another nice example, cocoa plants produce theobromine which kills dogs if they eat too much chocolate. The cocoa plant doesn't need to defend itself against dogs. 

    In a similar way, microbes from Mars could easily produce toxins that have adverse effects on Earth life. 
  • Life that out competes Earth life. One example here, what if Mars has some fourth form of photosynthesis different from the three main types on Earth.

    Our three types are:
    Green sulfur bacteria, which use light to convert sulfides to sulfur, which is then often oxidized to sulfur dioxide
    Normal photosynthesis which splits water to make oxygen, also taking up carbon dioxide in the process. (basic equation 6CO2 + 12 H2O → C6H12O6 + 6O2  + 6 H2O where the oxygen atoms in bold are the same ones on both sides of the equation - see Plants don't convert CO2 into O2, and Notes on lamission.edu)
    The photosynthesis of the haloarchaea which works similarly to the receptors at the back of our eyes, based on a "proton pump" which moves hydrogen ions across a membrane out of the cell using bacteriorhodopsin similar to the rhodopsin in our eyes, with no byproducts such as sulfur or oxygen, just creates energy directly from the proton gradient.

    What if Mars life uses a fourth form of photosynthesis is more efficient at making use of sunlight than the methods used by the green algae in our oceans? The space of possibilities is so vast, there is no way that DNA based life on Earth has explored even all the possibilities for DNA. For instance, over many millions of years, higher lifeforms in Australia never developed the placenta or anything resembling a modern mammal, and so it was vulnerable to introduction of rabbits, which were not at all adapted to Australian conditions, but still easily out competed the native Australian marsupials. Similar things could happen at the microbial level for transfer between planets instead of continents. Mars microbes could have capabilities never explored in the entire history of evolution on Earth. 

    For another example, if not based on DNA, it could be able to do more with less. The microbes might be smaller, the encoding more efficient, less need for error correction, enzymes much smaller to do the same thing, it could be all round more efficient, and so able to manage on less by way of resources, with a more efficient metabolism. It might out compete Earth life everywhere where it can survive on Earth, by making do with less. 
  • Life returned from Mars might have a different side to it, like harmless grasshoppers which some trigger can turn into locusts, some condition on Earth triggers a different behaviour or capability that never turned up when encountered on Mars or in transit. 
  • Life returned from Mars could be harmless at first, until it adapts to Earth conditions, but then evolve to be a major problem later. For instance it might need to adapt to warmth, or to water that is less salty than on Mars, or to lack of perchlorates (if it tends to depend on perchlorates for food) or the denser atmosphere.
  • It could be a slowly developing problem even without adaptation. E.g. back to that example of photosynthetic life that is just slightly better than Earth life, then it might take decades before sufficient numbers build up to replace the green algae and other photobionts in the oceans. Nevertheless, with exponential growth, there might be nothing we can do to stop its inexorable advance. 
  • Mars life could also be totally harmless, as Carl Sagan said in Cosmos, "There may be no micromartians. If they exist, perhaps we can eat a kilogram of them with no ill effects. But we are not sure, and the stakes are high. If we wish to return unsterilized Martian samples to Earth, we must have a containment procedure that is stupefyingly reliable...here are nations that develop and stockpile bacteriological weapons. They seem to have an occasional accident, but they have not yet, so far as I know, produced global pandemics. Perhaps Martian samples can be safely returned to Earth. But I would want to be very sure before considering a returned-sample mission.”

With this background, then you can see that ideas for quarantine just wouldn't work to keep Earth safe. There's a great tendency to look back at Apollo and assume we'd handle it as they did, put the astronauts in quarantine for a few weeks on return to Earth. But those quarantine precautions never had any peer review. They were published on the day of launch. And they were not even applied properly at the time. Buzz Aldrin noticed ants found their way into the quarantine facilities while he was in quarantine.

“The unit was comfortable, but there was little to do and nowhere to go, so we got bored in a hurry.

"One day, I was sitting at the table staring at the floor, and I noticed a small crack in the middle of the floor, with tiny ants coming up through it! Hmm, I guess this thing isn’t really tightly sealed, I thought. Imagine, if we had brought some sort of alien substance back with us, those ants could have contracted it and taken it back out to the world!”

Earlier, the command module hatch was opened when they landed, and dust from the Moon surely went into the sea at that point, and there were other breaches of protocols as well. But even if it was done perfectly, it wouldn't have protected Earth from microbes from the Moon on the remote chance that it had any.

If we were to attempt to use quarantine today, for samples or astronauts returning from Mars, then problems with this approach include:

  • If any of the astronauts become seriously ill, they will be rushed to hospital and not permitted to die in the quarantine facilities. If you try quarantine in orbit, they will be returned to Earth as soon as they encounter any really serious health issue. This is clear from Apollo. The crane they had designed to pick the command module out of the sea had a problem. Rather than fix the problem and leave the astronauts bobbing in the ocean, getting seasick while the world watched, they sent a helicopter with divers, who took the astronauts out of the module, into an open boat, and put them into their suits. By then the dust from the module would be in the sea already and planetary protection was already compromised even assessed by the standards of their time. From this example to show how mission planners were ready to waive precautions just to prevent the astronauts from getting seasick for a few hours while they fixed the problem, it's clear that they would definitely not let their heroic astronauts die in the quarantine facilities if they became seriously ill. So the Apollo astronauts quarantine was a largely symbolic gesture which would have done nothing to protect Earth from any real hazard in the unlikely case that the Moon did have microbes hazardous to Earth. 

    It's not clear you can ethically keep them inside anyway if they get seriously ill in quarantine facilities designed to protect Earth from unknown dangers. At the very least it's a very tricky ethical and legal area. Even if they consent beforehand to be left to die there to protect Earth, it's not clear you can hold them to that in the event that it happens, especially if you have no idea whether there is some extra terrestrial cause - when it might well be some Earth based illness that needs to be diagnosed in the advanced facilities of a modern hospital to save their lives. 
  • It only protects from diseases that affect humans or other lifeforms in the facility. You can't take all the higher animals we depend on, the trees, grasses, sea water, etc. etc. into the facility for testing
  • You have to guess at the latency period. Some diseases of humans such as leprosy can remain latent for decades before anything happens. There was no scientific reason for choosing any particular quarantine period for the Apollo astronauts. It was just a guess and I haven't seen any reasoning to explain their choice. Quarantine does work fine when you know the maximum latency period, and if it is a reasonably short period. But it doesn't work if that period is very long or you don't know what it is. 
  • It gives no protection from problems that manifest later. E.g. quarantine won't help at all if the microbes that humans carry with them need some time to evolve to adapt - either to terrestrial conditions or indeed even, to adapt to humans.

For all these reasons I think there is almost no point in attempting quarantine to protect Earth or to protect humans on Mars. It's largely symbolic and would give a false sense of security. It doesn't matter where you do the quarantine either, on Mars, or the journey back, or in orbit around Earth, or on the Moon, or back on Earth, none of that helps.

Instead I think there is no substitute for knowing what is in the samples before they are returned to Earth. I also think that we shouldn't send humans to Mars until we understand Mars conditions very well indeed and have done a reasonably complete biological survey of the planet, or for some other reason have a high level of confidence that there is no life there, or that any lifeforms there are safe for humans and for Earth. That's for safety reasons alone, apart from any other considerations, to protect both the astronauts and Earth (after they return).

Returning samples from mars - unlikely to find life if not already discovered

NASA has made it a priority for the next twenty years to return a sample from Mars for analysis on Earth. ESA has also proposed it as a flagship mission.

Artist's impression of Mars sample return vehicle launching from Mars - credit ESA.

However, with this background that we don't know where to look yet, for both early and present day life, and since Mars is such a complex planet, with such varied terrain to such, there is quite a risk that such a sample might fail to return material of biological interest. Probably we can only be reasonably confident of success if we have detected clear biosignatures on Mars already. Even if it contains organics, the organics might not arise from life.

So, if we want to find traces of life on Mars, it seems pretty clear, that we need to find it in situ on Mars first, just for reasons of expense. The NASA plans would return a few hundred grams of crushed samples at a cost of billions of dollars, and this is too much to spend to return a sample that has only a small chance of containing any material of interest to exobiologists.

It's true that once returned, we can analyse them over and again with more and more instruments - but that's only useful to exobiologists if we return the right samples in the first place. While we can send increasingly sophisticated instruments to Mars to study it in situ and explore a far wider range of possibilities there.

It's quite possible however, that ExoMars, or one of our other rovers, will find clear biosignatures of life on Mars. If that happens then exobiologists will probably be keen to return these samples to Earth for analysis. Can this be done safely?

Suggestion for protection of earth during sample return - ionizing radiation

I won't go into this in detail, why protection of Earth is needed, as you'll find plenty about it in my other articles, see Need for Caution for a Mars Sample Return - and Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisited

But in brief, life from Mars could be benign, but it could also be capable of competing with Earth life. In the worst (but most interesting case) Martian life could be XNA, capable of setting up an independent self contained ecosystem on Earth. Martian cells could also be far smaller than Earth life, as the earliest cells before the archaea must have been at most a few tens of nanometers across, about a tenth of the size of the smallest known modern cells (the ultramicrobacteria). Or, if it has a common origin with Earth life, could have capability of transferring genetic material via Gene Transfer Agents, as archaea are able to swap material very readily in this way, and the GTA's are again only a few tens of nanometers in size.

In the XNA specifications section of this paper: Xenobiology: A new form of life as the ultimate biosafety tool The authors talk about biosafety requirements for this procedure

"The ultimate goal would be a safety device with a probability to fail below 10-40, which equals approximately the number of cells that ever lived on earth (and never produced a non-DNA non-RNA life form). Of course, 10-40 sounds utterly dystopic (and we could never test it in a life time), maybe 10-20 is more than enough. The probability also needs to reflect the potential impact, in our case the establishment of an XNA ecosystem in the environment, and how threatening we believe this is."

Since XNA from Mars could also potentially set up an XNA ecosystem in the environment on Earth, we need to be similarly careful when considering its impact.

This all makes it extremely hard to contain reliably, especially when you don't yet have a thorough understanding of what it is you need to contain. It is not too bad so long as you keep the specimen in the capsule, but as soon as you remove samples for analysis, it's hard to see how you can keep it completely enclosed to ten nanometers level - as the optical resolution for the best high powered microscopes is around 200 nm. There's also the risk of damage to the capsule, and loss, theft, natural events such as hurricanes, or airplane crashes, or human error leading to accidental release.

Current requirements for sample return and legal situation

The most recent ESF study on how to deal with samples returned to Earth from Mars recommends returning them to a new type of facility which has to contain them right down to the level of GTA's as well as the smallest size of microbe they think is possible using unknown extra terrestrial biology. Their recommendations are that it has to be capable of containing particles well below the optical resolution limit of 200 nanometers (ideally it shouldn't permit release of particles over 10 nanometers in diameter). In other words, the facility has to be able to contain particles only visible with electron microscopes or similar. This is well beyond the capabilities of a normal biohazard level 4 containment facility where the aim is to contain known hazards of known size and capabilities. It also has to protect the samples against contamination by Earth life, even by a few amino acids.

Also, there's all the extra legislation to pass. Margaret Race looked at it. You'd be astonished, there are many domestic and international laws, needing to be passed - which were not needed for Apollo because the world nowadays is legally far more complex. After reading her paper, I think it could easily take well over a decade just passing all the laws even if everyone agrees and there are no objections, and surely longer if there are objections.

The basic idea here is that we return unsterilized samples from Mars to Earth before we know what is in them. To do that safely we have to design the sample return in such a way that the facility is safe to handle any conceivable extra terrestrial biology, before we have discovered even one other example of life other than Earth life. I think that's the main thing that makes this so tough. If we knew what we were returning, it would be so much easier. If the life on Mars is early pre-DNA life and if we can show it was made extinct on Earth billions of years ago, for instance, we might not need to take any precautions at all. On the other hand if it is not based on DNA or RNA at all, or if we had evidence that the life is at a stage of evolution several billion years ahead of Earth, or has capabilities Earth life doesn't have (such as more efficient photosynthesis) then it might need extreme caution.

Surely there is no substitute to finding out what is there first. So how can we do that? Well one approach is to use in situ searches, which may be the best way to search for life anyway - and then perhaps once we find life on Mars, by sterilizing samples returned to Earth.

Using ionizing radiation to sterilize the sample returned to Earth

However one possibility is to use ionizing radiation.

Ionizing radiation is not used for sterilizing spacecraft to Mars because gamma radiation destroys semiconductors. But with a Mars sample return, you don't need to sterilize an entire spacecraft. The only part that gets returned to Earth is the sample itself in its container. The rover remains on the Mars, just launches the container to orbit around Mars, and the container is picked up by a separate orbiting spacecraft.

So, my suggestion is, for the first sample returns from Mars, why not use ionizing radiation? Subject it to enough ionizing radiation to thoroughly sterilize even the most radioresistant microbes known such as radiodurans and chrooccocidiopsis or halobacterium. Modern analysis techniques would still permit us to learn a lot from a sample sterilized in that way.

Actually I'd subject it to more ionizing radiation than that. Radioresistant organisms on Earth don't seem to have adapted to high levels of radiation particularly, as they can never encounter those environments (except in very rare situations such as natural nuclear reactors in deposits of enriched uranium in the early Earth). Instead they probably developed radioresistance as a side effect of adaptations to extreme dry conditions and UV, which damage DNA in a similar way.

But on Mars any life would evolve radioresistance specifically in response to ionizing radiation. So, life on Mars may be even more resistant to radiation than the most radioresistant microbes on Earth.

The most extreme example of radioresistance on Earth seems to be Thermococcus gammatolerans - an obligate anaerobe from hydrothermal vents which was able to continue to grow after irradiation by 30 kGy of gamma radiation (applied at a rate of 60 Gy per minute).

Thermococcus gammatolerans - an obligate aerobe from hydrothermal vents, the most radioresistant organism known, able to withstand 30 kGy of gamma radiation, and still reproduce. That's about 400,000 years worth of surface radiation on Mars at the radiation levels detected by Curiosity during the current solar maximum of 0.073 Grays a year - possibly it could survive surface radiation for longer than that when you include periods of solar minimum.

This micro-organism didn't evolve in an environment with high levels of radiation, but developed this resistance as a side effect of other effects that can damage DNA. Microbes on Mars would have evolved in an environment with high levels of radiation, and adapted specifically to that environment. They might be even more radioresistant than this.

So, it looks as if you'd need to use at least hundreds of kGy to be safe. There wouldn't be much left of complex molecules after that, sadly, such as the carotenoids, but the chiral signal of amino acids would be strong, even after 14 MGy. If these are samples of early life on Mars, then 14 MGy is approximately the dose the microbes received anyway from natural nucleotides in the rocks. So, for samples of ancient life, a radiation dose of a few MGy is maybe not much of an issue, except for the remote possibility of revivable ancient life, or life retrieved from pure ice, or from salt deposits with no radioactive isotopes in them.

So - that's my suggestion. For the very first sample returns from Mars, when we have very little idea of what is in them, the idea is to irradiate it with several MGy of radiation before you open it.

Safest of all would be to irradiate it in Mars orbit, before it returns to Earth, perhaps with gamma radiation, using Cobalt 60, as is standard in food and medical gamma ray sterilization. One idea, the Cobalt 60 could be included in a shielded container sent along with the spacecraft that picks up the returned sample in Mars orbit. That way, even before the sample leaves Mars orbit, it is put straight into the container along with the Cobalt 60 source, with the whole thing surrounded by thick layers of lead to protect the spacecraft itself from the radiation.

As is usual for Mars sample return proposals, you would do this in such a way as to break the chain of contact with the Mars surface. When the orbiter picks up the capsule, it carefully positions one capsule inside the other in the vacuum conditions of space without ever letting the exterior of the capsule touch any other part of the orbiter. So then only the interior of your return capsule, the part strongly irradiated with Cobalt 60 during the return journey, has any contact with material which has touched the Mars surface.

I don't know if that is practical; it is just a suggestion. The advantage is that it would be far less damaging to the sample than heat sterilization. Also sterilizing at Mars deals with the issue that the capsule could be damaged by a micro-meteorite during the return journey. It also replaces the immense complexity of the Mars handling facility on Earth with a relatively simple addition to the sample return mission.

You still want to take every possible care when handling it, and you might as well still return it to a biohazard handling facility (after all it might have harmful bioactive chemicals in it still). But the chance of release of extraterrestrial life with the ability to reproduce on Earth seem remote even at the 1 in 1020 level when you have a sample already thoroughly sterilized with gamma rays - and you no longer need to attempt the perhaps almost impossible task of containing it at the 10 nanometer level.

If you want to do DNA sequencing of present day life, or perfectly preserved early life - or even XNA sequencing, you can do that on Mars using the ideas for a miniaturized DNA sequencer to send to Mars (SETG, already built and pretty much ready to fly). If you want to revive revivable ancient life, again do that on Mars, and other experiments that need unirradiated specimens would be done on Mars to start with.

Subsequent sample returns

After the first samples are thoroughly studied, then the situation can be reviewed. But probably we should continue to apply extreme caution until we have a very thorough understanding of the situation on Mars, because there might be a variety of forms of life on Mars.

For instance if the first sample contains DNA based life, this doesn't rule out the possibility that Mars also has XNA based life. You can easily imagine a scenario where past XNA life co-exists on Mars with more recent DNA based life introduced on meteorites, for instance, either in different habitats or in the same microbial colonies - and the XNA life might be hazardous for Earth life, and never made the transition here via meteorite.

I'd suggest that we need to continue to take these precautions even if we think the chance of contamination of Earth is extremely low. After all even if there is as little as a one in a billion chance or less of returning XNA to Earth able to out compete Earth DNA and establish a separate ecosystem here or take over from some Earth life-forms - that would still be a completely unacceptable level of risk to take according to many ways of thinking.

This is just a suggestion which I present for discussion. 

Would this ionizing radiation, perhaps 2 or 3 MGy or so, be sufficiently sterilizing to make a sample return from Mars completely safe for Earth life even at, say, the 1 in 1020 level that seems necessary for novel existential risks? Would it also preserve the science value of the sample? What do you think?

Another possibility though might be to return unsterilized samples to cislunar space, but not to Earth itself.

Suggestion to return samples to above GEO

I think that given that we have no experience at all in handling extraterrestrial biology, that it's better not to return them to Earth at all, but what if we return it instead to a telerobotic facility above GEO - furthest in terms of delta v from Earth or the Moon of any point in cislunar space?

We could return some samples to Earth right away so long as we sterilize them first. So that should satisfy the geologists. I suggest using ionizing radiation to sterilize them, as that happens anyway on Mars, and would still preserve some evidence such as chirality and complex chemistry to show that there was life there before it was sterilized, if that was the case. And easy to take account of for the geologists, who already disentangle the ionizing radiation effects of the journey from Mars to Earth when studying Martian meteorites.

If they are shown to be harmless quite quickly, we just return them as is, much as we did with the Moon rocks. This saves years of legislation (probably a decade or more to pass all the laws), and hundreds of millions of dollars of expense for designing, building and operating a facility that is never needed.

Returning to above GEO simplifies all that as no new legislation is needed, can be done within all the existing laws. Also, you don't have any concern about the staff not using the right protocols because it is all operated from Earth and there is nothing the staff could do by mistake or laziness that would lead to life from the facility escaping into the environment of Earth.

Yes, a plan to return to a facility above GEO would add to the expense of the mission, but nothing like as much as to a surface facility. The orbital facility could just be a single spacecraft that receives the sample, and does preliminary studies. Since some of the plans involve sending a spacecraft up to collect the samples anyway, it might not cost that more at all.

Then it's an open ended future after that. So any stages after that, to study the sample once it is in orbit, can be treated as extended missions. So this also reduces the up front cost and makes it much more likely to be accepted for funding. So I think this idea that a mission to return it to a spacecraft in a safe orbit above GEO for preliminary study would be the simplest one and lowest cost and most likely to be approved.

While if we decide that the samples are potentially hazardous for the environment of Earth, then by the time we do this, in the 2030s at the earliest, then it should be easy to send hundreds of tons of equipment to above GEO to study the samples, and this could be the basis of an international operation to study them in orbit via telerobotics if they turn out to be potentially harmful to Earth.

In that case we would design the facility on Earth around understanding of what is in the sample, or maybe just continue to study the samples above GEO. Either way we save major expense on designing a facility to handle any possible form of exobiology, and instead design our facility, on Earth or above GEO based on whatever is needed to contain an already studied sample. And if we do decide that the material can be returned to Earth in viable form for study as living organisms on Earth, then this will be for a known biology, so the legislation needed could be passed more easily.

For instance if it is viable early life, based on RNA or even just primitive autopoetic cells, it might be easy to establish at an early stage that there is no possible hazard for Earth at all, in which case perhaps it doesn't need to be studied in a biohazard containment facility at all, but just protected to keep Earth life out of the sample.

About the only thing that could damage and release the sample above GEO is an impact but there wouldn't be any risk from spacecraft debris, as any debris in GEO or the graveyard orbit a few hundred kilometers above GEO wouldn't travel far - those spacecraft are pretty much stationary relative to each other.

You'd place it far enough above GEO can put it out of way of any debris from defunct GEO satellites. So the chance would be very low of an impact leading to release of the material from the sample, only from natural debris from asteroids and comets, and being a spacecraft it could also maneuver to avoid such hazards like the ISS.

For more details see my:

Will NASA's Sample Return Answer Mars Life Questions? Need For Comparison With In Situ Search
No Simple Genetic Test To Separate Earth From Mars Life - Zubrin's Argument Examined
How To Keep Earth Safe - Samples From Mars Sterilized Or Returned To Above Geostationary Orbit - Op Ed

Need For Caution For An Early Mars Sample Return - Opinion Piece
Concerns for an Early Mars Sample Return - background material
Mars Sample Receiving Facility and sample containment
Mars Sample Return - Legal Issues and Need for International Public Debate

If there is Life in Venus Cloud Tops - Do we Need to Protect Earth - or Venus - Could Returned XNA mean Goodbye DNA for Instance?

Or return samples to the Moon

Hazardous Biology Facility on the Moon, telerobotically attended, surrounded by vacuum - Artist's impression, illustration by Madhu Thangavelu and Paul DiMare © from The Moon: Resources, Future Development and Settlement

If you return samples to a human occupied base on the Moon, then it's got the same issues as returning them to a human occupied facility anywhere.

As with anywhere else, like the above GEO idea, quarantine simply can't work unless you know what is in it and what precautions are needed. Even if they agreed, it's not at all clear you can ethically or legally commit humans to stay there for the rest of their lives, should it turn out to be potentially hazardous for humans or any other creatures or the environment of Earth (e.g. carried to Earth on the skin or inside bodies of humans). What do you do if they become ill and Earth is the only place they can be treated effectively?

But if you return it to a robotic facility on the Moon - well now, it's far better isolated than anything we could achieve on Earth, yet perhaps easier to build and work with than a large facility in orbit, especially if we develop infrastructure on the Moon. As with the facility in orbit, then it's fine to build it first, and then to send instruments to it, so long as it only goes that way, and any materials are sterilized in the reverse direction.

It could be useful for any hazardous biology generally, like an extra biohazard level above biohazard 4. So for instance if we wanted to experiment with synthetic biology using XNA in place of DNA, then we could use a facility like this on the Moon, to minimize any risk of it affecting Earth.

Even if the life did escape from the facility, e.g. after a meteorite strike, where would it go? About the only way it could be transported is via the levitating lunar dust, but that would surely be thoroughly sterilized by UV radiation before long. You could also turn the region around the facility into glass and remove any dust that strays onto that glass regularly.

You would have to think about the effects of larger meteorite strikes. And it would need to be evaluated by exobiologists, but seems very promising to me for hazardous biology!

One other suggestion, what about putting the hazardous biology facility in a lunar cave? There are many cave entrances discovered on the Moon now, and some of them might be not needed for human habitats and just lead to a small cave the right size for the facility. It might have smooth walls like a lava tube. Ideal for the facility. Protected from impacts by all except the very largest of the near Earth asteroids. And you could use a liquid airlock for the entrance, to have air inside as would be needed perhaps for some of the machines, but no risk of dust / air getting out onto the surface.

Returning samples to the Moon is a lot safer than returning them to the Earth's surface. However, the COSPAR guidelines for category 5 (sample return) missions currently say that

"(The Moon must be protected from back contamination to retain freedom from planetary protection requirements on Earth-Moon travel)".

So before samples can be returned to the Moon, that would need to be discussed and the guidelines altered. One issue I can see that would need to be looked into in detail is - what if the sample return mission crashes on the Moon somewhere different from its intended landing site?

Search for early life on Ceres, our Moon, or the moons of Mars

Though Mars is the most obvious place to look for evidence of early life, there are other places we can look too. First there's a chance that Ceres was the origin of life for both Mars and Earth. It seems to have got off lightly in the bombardment by giant meteorites in the early solar system, and likely to have had hydrothermal vents, and large amounts of water. And Hubble has recently detected water escaping from Ceres, so it has liquid water as well, in the present day solar system.

With these discoveries, Ceres seems a prime target for the search for origins of life.

Earth, Moon and Ceres to scale, for comparison. One theory suggests that Ceres could be the origin of life for Earth and for Mars. The Moon could be interesting for the search for life also, as it would preserve meteorites from impacts on early Earth, also on Mars and probably Venus too from the earliest solar system.

Then, during the Late Heavy Bombardment, large meteorites impacting on Mars, Earth, Venus, must have sent rocks throughout the solar system. After the Moon formed, it was a prime target for these rocks to land on. So we might well find meteorites from any of these places on the Moon. Perhaps a particularly good place to look might be the lunar poles, where the ice deposits would help to keep the meteorites from drying out - and search for meteorites deep below the surface, protected from cosmic radiation.

The same applies to Mars' moons. Phobos particularly might well have meteorite debris from early Mars which could possibly tell us things about the early Noachian period on the planet. See Why Phobos Might be the Best Place to go for a Sample Return from Mars Right Now

Life appearing many times

On Earth we are used to the idea of a single genesis of life, over four billion years ago, with all present life derived from it .But is that typical of a planet with life on it? After all with the shadow biosphere hypothesis, Earth could have two distinct forms of life living here at the same time. Distinct in the sense that they don't speak the same language or use the same structures at a cellular level.

If Mars ever developed life as robust and varied as DNA based life on Earth, then it is probably still there. Even so, the conditions are so harsh that some of the habitats could be uninhabited. We do have uninhabited habitats on Earth - newly formed volcanic rock may be free of any life, even microbial, for a short time after it forms. On Mars, when a new habitat forms, such as a RSL, or flow like feature, perhaps it might take a longer time for life to get there than it does on Earth. If life is rare on Mars and there are few spores in the dust, then it might take quite a while. Indeed you could imagine a situation where some of the RSL's on Mars are inhabited, some uninhabited, and different RSL's are even inhabited by different lifeforms. Also habitats that seem similar may actually form in different ways. What if all three of the main hypotheses for RSL's just describe different ways they form? Some due to hot spots leading to liquid water from the deep hydrosphere reaching the surface by repeated sublimation and refreezing. Some due to ancient ice from times when Mars was so tilted in its axis that it had equatorial ice sheets. Some due to salts that deliquesce in the night time humidity of the very cold though thin air on Mars.

  • Present day life with different form of photosynthesis and comparison with synthetic life made in labs on Earth
  • Unlikely life on Mars has reached the exact same stage of evolution as us and could be either more evolved or less (even if microbial and lichens it could be more evolved or less evolved microbes)
  • How it is easy to argue that case both ways based on the different history of Mars
  • That the most vulnerable type of life we could find on present day Mars - early life - could go extinct maybe quite soon after contamination with Earth life

Also, what if Mars never developed life as robust as modern Earth life? Then life may have evolved, for instance in the hydrothermal vents, then gone extinct when the vent was no longer active. Then perhaps it evolved again from scratch around another vent. Perhaps evolution happened in slow motion until eventually, millions of years later, more robust forms developed that could survive the end of activity of the birth place hydrothermal vent.

Also if Mars life never developed photosynthesis, then the search for past and present life there may be elusive. Another possibility though is that Mars life evolved further than Earth life. If so, well its life may have novel capabilities our life doesn't have. Perhaps just more diverse pathways and more complex life, even if microbial. Perhaps just that it has a new form of photosynthesis. We have three types of photosynthesis

  • Present day life with different form of photosynthesis and comparison with synthetic life made in labs on Earth
  • Unlikely life on Mars has reached the exact same stage of evolution as us and could be either more evolved or less (even if microbial and lichens it could be more evolved or less evolved microbes)
  • How it is easy to argue that case both ways based on the different history of Mars
  • That the most vulnerable type of life we could find on present day Mars - early life - could go extinct maybe quite soon after contamination with Earth life

The most vulnerable early life on Mars

The most hazardous early life on Mars

Earth life that could contaminate Mars habitats

None of this would matter if Mars was so different from Earth that no Earth life could survive there. For Earth life to survive on Saturn's moon Titan would indeed be like sharks surviving in the Savannah. Temperatures there are well below the temperatures for Earth life and the only water is thought to be in the form of solid rock, while the fluid is ethane or methane. There would be no issues with contaminating Mars if conditions there were like Titan. But no, it's actually rather habitable for Earth life - for extremophiles that is. Though no animals or humans, birds, insects could survive on Mars, and most plants couldn't either there are some lichens and microbes from Earth that would fit in and be right at home there - in the right situation.

If these habitats do exist and are habitable, there are many Earth microbes which have been shown to be able to survive in Mars simulation conditions, and so could potentially survive there, contaminate them and make it difficult or impossible to study them to find out what was there originally.

Researchers at DLR (German equivalent of NASA) testing lichens in Mars simulation experiments. They showed that some Earth life (lichens and strains of chrooccocidiopsis, a green algae) can survive Mars surface conditions and photosynthesize and metabolize, slowly, in absence of any water at all. They could make use of the humidity of the Mars atmosphere.

Though the absolute humidity is low, the relative humidity at night reaches 100% because of the large day / night swings in atmospheric pressure and temperature.

Here is a list of some of them, for the cites see my Candidate lifeforms for Mars in my Places on Mars to Look for Microbes, Lichens, ...:

  • Chroococcidiopsis - UV and radioresistant, and can form a single species ecosystem. It needs no other forms of life, and only requires CO2, sunlight and trace elements to survive.
  • Halobacteria - UV and radioresistant, photosynthetic (using hydrogen directly - proton pumps, doesn't generate oxygen or sulfur), can form single species ecosystems, and highly salt tolerant. Some are tolerant of perchlorates and even use them as an energy source, examples include Haloferax mediterranei, Haloferax denitrificans, Haloferax gibbonsii, Haloarcula marismortui, and Haloarcula vallismortis
  • Some species of Carnobacterium extracted from permafrost layers on Earth which are able to grow in Mars simulation chambers in conditions of low atmospheric pressure, low temperature and CO2 dominated atmosphere as for Mars.
  • Geobacter metallireducens - it uses Fe(III) as the sole electron acceptor, and can use organic compounds, molecular hydrogen, or elemental sulfur as the electron donor.
  • Alkalilimnicola ehrlichii MLHE-1 (Euryarchaeota) - able to use CO in Mars simulation conditions, in salty brine with low water potentials (−19 MPa), in temperature within range for the RSL, oxygen free with nitrate, and unaffected by magnesium perchlorate and low atmospheric pressure (10 mbar). Another candidate, Halorubrum str. BV (Proteobacteria) could use the CO with a water potential of −39.6 MPa
  • black molds The microcolonial fungi, Cryomyces antarcticus (an extremophile fungi, one of several from Antarctic dry deserts) and Knufia perforans, adapted and recovered metabolic activity during exposure to a simulated Mars environment for 7 days using only night time humidity of the air; no chemical signs of stress.
  • black yeast Exophiala jeanselmei, also adapted and recovered metabolic activity during exposure to a simulated Mars environment for 7 days using only night time humidity of the air; no chemical signs of stress.
  • Methanogens such as Methanosarcina barkeri[200] - only require CO2, hydrogen and trace elements. The hydrogen could come from geothermal sources, volcanic action or action of water on basalt.
  • Lichens such as Xanthoria elegansPleopsidium chlorophanum, and Circinaria gyrosa - some of these are able to metabolize and photosynthesize slowly in Mars simulation chambers using just the night time humidity, and have been shown to be able to survive Mars surface conditions such as the UV in Mars simulation experiments.

Most of these candidates, apart from the lichens, are single cell microbes (or microbial films). The closest Mars analogue habitats on Earth such as the hyper arid core of the Atacama desert are inhabited by microbes, with no multicellular life. So even if multicellular life evolved on Mars, it seems that most life on Mars is likely to be microbial.

For more about the value of Mars for biology and implications of sending humans there, see

Idea that we have contaminated mars too much already, so there is no point in protecting it

It's surely true that there is Earth life there already from our spaceships. But our planetary protection measures take this into account. Carl Sagan's aim was a 1 in 10,000 chance of contaminating Mars per mission and a 1 in 1000 chance of contaminating it during the exploration period. It never was to be 100% sure we can't contaminate it. Of course ideally that is what we'd want it to be. But we can't do that at present. I think we should aim for 100% myself for Europa and Enceladus by sampling the plumes rather than landing. But for Mars the die is cast. However, the chance is probably something like 99.9% certain that it is not yet contaminated.

So even with Viking it was done on a probability level. The decision to stop sterilizing to Viking level was done on the basis that conditions on Mars are so harsh that they correspond to the heat sterilization stage of the Viking lander. Critics say that they stopped protecting Mars after Viking, but that's not true or was not the intention at least. We still have planetary protection officers and regular biannual meetings of COSPAR to protect Mars and the rest of the solar system.

What happened is that before Viking they didn't know quite how hostile conditions were there. After Viking, they came to the conclusion that such measures of sterilization were only needed if the spacecraft contacts regions in Mars that could be habitable for life - and Viking level sterilization is still the requirement for those "Special regions". For other spacecraft like Pathfinder, Opportunity, Spirit, Phoenix, and Curiosity, they sterilized them to the pre-heat treatment stage on Earth for Viking. Then they count on the harsh environment on Mars for the rest of it. They did give up on the use of probabilities pioneered by Carl Sagan et al, because of the impossibility of assigning a probability to life contaminating Mars, but the basic objective is the same to have a tiny chance of contamination, of the order of 1 in 1000 for contamination during the "exploration phase" of perhaps 57 ground missions an 30 orbiters (Carl Sagan's figures). Even though we've had crashes on Mars, they also were probably sterilized pretty much during the re-entry and crash itself.

So that question about what counts as too much contamination is something the exobiologists have already looked at and written many papers about.

The current guideline, for Curiosity and for all other missions to the surface (apart for those that search for present day life which have stricter requirements) is to reduce the bioburden to 300,000 bacterial spores on any surface from which the spores could get into the Martian environment. Any heat tolerant components are heat sterilized to 114 °C. Sensitive electronics such as the core box of the rover including the computer, are sealed and vented through high-efficiency filters to keep any microbes inside.

That is a level of protection we can do with rovers and landers. It is totally impossible to achieve that once you have humans on board.

Could we have contaminated Mars already?

Mars has turned out to be a bit more hospitable than we thought. So that raises the prospect - what if it is already contaminated? I think the Phoenix lander is the most likely to have done so, or alternatively the Mars Polar Lander because it crashed in polar regions. After all Phoenix observed what seemed to be droplets of liquid salty water on its legs.

Possible droplets on the legs of the Phoenix lander

Also Phoenix got crushed by the advancing dry ice in winter, as was expected for its location

    Phoenix lander crushed by frost - layers of dry ice forming on the solar panel in winter snapped one of them of and it was not expected to last the winter - the right hand image shows it two years after the 2008 landing in 2010.

If any of our landers have contaminated Mars, I'd have thought Phoenix was a likely candidate. As usual it was sterilized to high standards, but before Phoenix nobody realized there was any possibility of liquid there, now we realize that liquid brines are a distinct possibility, also droplets of water on salt / ice interfaces. Most of those are probably either too salty or too cold for life but are there any that Earth life could survive in? We just don't know. Experiments show that it is possible to achieve habitability but it depends on the particular mix of salts.

    Jim Young (left) and Jack Farmerie (right) from Lockheed Martin, working on the Phoenix lander science deck under clean room conditions to protect Mars, following planetary protection guidelines. Credit: NASA /JPL/UA/Lockheed Martin.

    However nobody knew back then that liquid water could form on the surface in those regions. The entire polar regions of Mars are now declared a "Special Region" meaning that landers there need Viking level sterilization for anything that could potentially contact a habitat. Has Phoenix contaminated Mars? The consensus seems to be that probably it hasn't, but it's site would be an ideal one to visit to check how effective our measures to date have been.

I think myself that a priority mission for planetary protection is to send a lander to investigate one of these sites. If Phoenix, say has started to contaminate Mars we might find a small enclave of life around the lander. I think that it is high time that we actually had a mission to the surface to actually test to see how effective our planetary protection measures are. The mission could be dual purpose, first to search for life habitats, past and present life signs etc - so it would land some distance away from Phoenix - then it would travel up to the crashed lander, photograph it, and analyse the remains and test for liquid water droplets and for signs of life, and examine the spacecraft itself for viable life there.

What if we have contaminated Mars?

First, if there is Earth life there already, brought on our landers - the last thing we should do is to introduce new life. For instance if it has been contaminated by a photosynthesizing green algae, well perhaps that plays nicely with much of the Mars life. Even if what we have there is a vulnerable RNA world that has been made extinct on Earth, well whatever there is obviously well adjusted to oxygen, including the perchlorates and hydrogen peroxides. A little oxygen from green algae is not likely to bother it. The green algae as primary producers are not likely to harm it, may even be a source of food, creating new organics from just sunlight, CO2 and trace elements.

This doesn't mean that it is okay therefore to introduce all the microbes on a human occupied spaceship that would get there after a crash on Mars. That's like saying that if you introduce rabbits to an island, then that's the end of any attempt to protect it from invasive life, so you might as well introduce rats, cane toads, goats, cats etc. There may be many things that are vulnerable to rats, cats etc that are not harmed by rabbits.

Or it's like, if you are overrun by kudzu, the answer is to say okay, let's have Japanese knotweed, let's have Himalayan Balsam, let's have every single invasive species that ever causes problems as obviously it's all over now.

A gardener or farmer would not do that. Instead you'd minimize the effects of the kudzu as much as you can and do whatever you can to prevent the other species from invading.

In the same way if we find that Phoenix has introduced life to Mars, or any of our other landers or crash sites there - then the first priority would be to see if we can limit or reverse the damage. The life would be slow growing in such harsh conditions. Perhaps we could sterilize it with ionizing radiation or similar. We could take a high intensity gamma radiation emitter to Mars and use that to sterilize the immediate vicinity around the lander. Who knows, maybe it is not too late and we can sterilize and reverse the contamination completely. And if not, we manage it as much as we can, slow it down as much as we can, and make sure we don't introduce any other invasive microbes to Mars.

This is keeping our options open for the future.

Myth of automatic terraforming

This is the idea that if you add microbes to a planet, no matter what they are, that it will automatically turn into a second Earth or the closest to Earth that's possible for the planet. I call that the "myth of automatic terraforming". To see why that is not automatic, think of a future Earth too hot for life, a billion years into the future. It would just have extremophiles.

Just possibly there might be some biological way to do something about this to cool down that future Earth using microbes - but why would just adding a lot of microbes from present day Earth cool it down automatically? If it could sort itself out, it would have done it already. Mars may well have life already, and if so, it has not terraformed it, and why then would life from Earth terraform it if its own native life has not?

Adding life to a planet could push it in many different ways and there is no way of knowing if it would make it better or worse. The one thing it definitely does do though is to close off future options. After you've done that, you can never roll back, if you later find that one of the lifeforms you introduced is a major problem on the planet. Not with microbes. It is hard enough to roll back higher lifeforms like rabbits, cane toads, rats, Kudzu or Japanese knotweed. Even camels are a problem in Australia since the continent is so huge. How could you roll back a problem microbe from a planet as large as the land area of Earth?

What will you do if you have introduced some problem microbe? Maybe you want to increase oxygen levels but you introduced aerobes that eat the oxygen? Maybe you want to increase methane levels but you accidentally introduced methanotrophs that eat it? Maybe you introduced secondary consumers that eat the algae that you want to use to introduce oxygen. Many things could go wrong as a result of microbes you introduced by mistake.

    Imagined colours of future Mars. This is just to suggest the idea that there could be many possible futures and accidental or intentional attempts to transform the planet could push it in many different ways, and we might not have much control on what happens after that especially if something takes it in an unexpected direction.

    The one in the middle is the aim of terraforming. But it could as easily be any of the others or something else altogether. And once we start to introduce life to Mars, there is no way to take any of it back again if it causes problems, or evolves rapidly into something problematical. See Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?

As one simple example of how microbes introduced by mistake could mess things up quickly, some bacteria convert water to calcite, and if you introduce them by mistake, you might find that these microbes have converted all the underwater aquifers to cement. That's an example from Cassie Conley, current planetary protection officer for the USA - she is a microbiologist / astrobiologist.

Going to Mars Could Mess Up the Hunt for Alien Life

I think this is based originally on Lovelock’s Gaia hypothesis in its strong form, the idea that life makes planets more habitable for itself. The weak Gaia hypothesis that the Earth has many systems that work together to help keep it in a habitable state, mediated by life, is widely accepted. But the idea that such a system arises automatically on all terrestrial planets with life is not at all universally accepted. That’s the “strong Gaia hypothesis”. Some things about our own planet are puzzling, for instance, why did photosynthetic life evolve at just the right time to turn a CO2 into oxygen, to cool our planet to keep it habitable, instead of arising too soon, to make it too cold, or too late, leaving it too hot? Then in science fiction the strong Gaia hypothesis has been exaggerated to mythology, the idea that introducing life to a planet not only helps keep it habitable for that life, but that it also automatically makes it habitable for humans too. Why?

If life made Mars as habitable as it possibly could - the atmosphere would be methane, not oxygen

The way to make Mars the most habitable it could be for life would be for methanogens to evolve to convert all the atmosphere to methane, which is a strong greenhouse gas. That would make Mars nearly as warm as it could be, using natural methods, though if the strong Gaia hypothesis was true, then surely also the life would evolve to generate stronger and stronger greenhouse gases on Mars to keep it warm. That would make it more habitable, but not an environment humans could live in.

    We may have spotted methane on Mars. If so this figure from NASA / JPL shows possible sources. One possibility is methane clathrate storage. It's possible that early Mars had large amounts of methane in its atmosphere which helped keep it warm. The only natural way for a Martian version of Gaia to keep it warm today is through generating greenhouse gases. 

    If so, a methane atmosphere is one way it could do it, or some other stronger naturally produced greenhouse gas. The result would be habitable possibly for ancient Mars life, but not for humans. This could be a way to "Mars form" Mars to return it to conditions that it enjoyed in the early solar system. But if so, whatever lead to the methane disappearing would probably happen again. The idea that life on a cold planet like Mars would automatically produce methane to keep it warm would be a very strong version of the Gaia hypothesis.

That would be a very strong version of the Gaia hypothesis - the idea that life on planets like Earth evolve oxygen generating photosynthesis to make it colder as it gets too warm, and life on cold planets like Mars evolves methanogens to create greenhouse gases to warm it up. Mark Waltham has argued that it is probably much more a matter of luck, at least partly, on Earth that life converted carbon dioxide in the atmosphere in to oxygen at just the right time to cool it down.

If it was true, it would not be too promising for making Mars Earth-like as it would tend to converge back to a methane rich atmosphere.

With this background, then introducing Earth life to Mars would probably do nothing to make it more habitable, not without some long term plan, megaengineering, and careful selection of which lifeforms to introduce when. You can't just leave it "up to Gaia" to do it for you, as even on the strongest possible Gaia hypothesis, then it can't create an oxygen rich Mars because it would be too cold out there. It would probably need artificial greenhouse gases or large planet scale mirrors or both to remain warm enough long term. In a thousands of years project that then goes on and on, trillions of dollars a year keeping it habitable. And what do you do if it begins to go in some unexpected direction? It is a major issue on Earth just to keep the levels of carbon dioxide at the correct values from rising at levels of only 400 parts per million.

I think it is great to think about terraforming ideas, yes. It helps us learn a lot about our planet and exoplanets and Mars itself to do those thought experiments. But as for practical experiments, let’s start a lot smaller. We haven’t yet managed a closed system ecosystem the size of Biosphere II on Earth. Once we have very small closed system ecosystems on Earth, then we can try it in space also, for instance in the possibly vast lunar caves, as vast as an O'Neil cylinder.

    Artist's impression by Don Davis of the interior of an O'Neil style cylindrical space colony - from Space Colony art of the 1970s. The caves on the Moon may be as vast inside as this, in the low gravity, several kilometers in diameter. The Grail radar data suggests the possible presence of lunar lava tube caves over 100 kilometers long.

    So, lunar caves could potentially be as vast as an O'Neil cylinder . If so, maybe some day we could have colonies like this on the Moon, easier to construct than an O'Neil cylinder - though probably multiple tiered and of course nobody living upside down on the roof. The lighting for the caves could come from solar collectors on the surface channeled through optical fiber to the caves during the lunar day - and then from efficient LED lights at night powered either from stored fuel cells or power from strips or patches of solar panels that circle the Moon round to the day side - easy to make in the hard vacuum, solar panel paving rovers, see Solar cells from lunar materials - solar panel paving robot

    Though vast, such a project is nevertheless far far smaller than the planetary scale megaengineering needed for terraforming. It is also a project that could be completed in decades. A terraformed planet would take thousands, or hundreds of thousands of years to completion. On Earth the process took millions of years.

    If we can't make O'Neil cylinder type habitats or their analogues in lunar caves, we have probably got nowhere near the capability needed to terraform a planet.

Then we can work up to larger maybe city dome or Stanford Torus type ecosystems. Eventually we can try Terraforming and paraterraforming the Moon. Let’s leave off ideas to terraform planets until we know a bit more.

Pristine Mars

And - let’s keep Mars pristine for scientific study at least until we know what is there. Otherwise we may mess it up for future transformation, if we do try to change it, and we may also spoil the opportunity to make the next big discoveries in exobiology. It may be the equivalent of an exoplanet on our own doorstep in terms of the discoveries we could make there. So let’s keep it like that, not try to make it into a pale shadow of Earth before we know what’s there.

I fully understand how those who are keen on colonization of space want to land humans on Mars as soon as possible. They’ve been looking forward to this for decades some of them. They may be so keen on this that they think that it is far more important than any discovery in biology.

But we aren’t talking about preserving some obscure microbe only of interest to microbiologists. What we discover there could lead to the biggest discoveries in biology of this century. It could be as big a discovery as the discovery of evolution or the spiral structure of DNA.

It’s only because introducing life to Mars is irreversible that we are in this situation. Their keenness to colonize Mars doesn’t give Elon Musk or Robert Zubrin or anyone else the right to make an irreversible decision about Mars for the rest of humanity. We are in it together and we all have a right to a say in this decision. The situation is particularly acute because there is a significant risk of a crash of the first human missions to Mars if we do send humans to the surface. See Why Do Spacecraft Crash On Mars So Easily? A crash of a human occupied ship would be the end of planetary protection of Mars for science.

Searching for a non confrontational way ahead

At the moment, there's a tremendous impetus amongst Mars advocates to get to Mars as soon as possible. Elon Musk even hopes to send humans to the Mars surface as soon as the 2020s, recently suggesting a first human mission in 2024, with NASA talking about the 2030s. I think it would be wrong though to suggest that Elon Musk doesn't care about the science impact of introducing Earth microbes to Mars. Here he answers a question on this topic, in the 2015 AGU conference in San Francisco, 30 minutes into this video:

Q. "I am Jim Cole from Arizona State University. I was listening to Chris McKay, another advocate of humans to Mars, and he was talking about how if we do go to Mars and we find life either there or extinct, we should consider removing human presence so that we can allow the other life to thrive. I was wondering what your thoughts on that were. "

A. "Well it really doesn't seem that there is any life on Mars, on the surface at least, no sign of that. If we do find sign of it, for sure we need to understand what it is and try to make sure that we don't extinguish it, that's important. But I think the reality is that there isn't any life on the surface of Mars. There may be microbial life deep underground, where it is shielded from radiation and the cold. So that's a possibility but in that case I think anything we do on the surface is not going to have a big impact on the subterranean life.".

So, it's clear (as I'd expect actually), he does think it is important we don't extinguish any native Mars life. But he thinks there isn't any present day life on the surface. But is that right?

I did a survey of the scientific literature, to see what there is by way of proposed habitats and to investigate the range of views on the topic:

Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,... (long detailed survey article with many cites)

It's also available as a kindle booklet, and also online here with table of contents

As you see, there's an almost bewildering variety of suggestions for habitats on Mars for life. The main ones are (these links take you to the online booklet)

There's a wide variety of views also on the topic of whether any of these are habitable, and whether they actually have life in them, from almost impossible to very likely, see Views on the possibility of present day life on or near the surface, and for the idea that they may be inhabitable but uninhabited, see Uninhabited habitats.

So when will we resolve this? Well not for some time. Most of these potential habitats would be hidden from view, a few millimeters or centimeters below the surface. Some of the habitats might be quite productive, for instance methanogens in warm humid locations deep below the surface heated by geothermal processes. There might be enough life there to cause obvious effects on the atmosphere, such as the methane plumes. But as Mars changed from a warmish wet planet to a cold dry planet, any surface life would probably become more and more sparse, and have less and less effect on the atmosphere.

As Mars slowly changed from the warmish humid planet on the left to the dry cold planet on the right, then any surface life may have become more and more sparse, and had less and less effect. Image from NASA (Goddard space center).

So, if the life from early Mars still lingers but is sparse, it might easily have almost no effect on the atmosphere by now. The most habitable areas of Mars such as the warm seasonal flows, if we are lucky, might be about as habitable as the Antarctic dry valleys or the high Atacama dry desert. If that's the way of it, life in those few square kilometers of the Martian surface would have almost no effect on the atmosphere. Mars already has small amounts of oxygen (0.145% as measured by Curiosity). The signal of oxygen from photosynthetic life on the surface, at such low levels, would just be hidden in the noise.

Indeed, even if the entire surface of Mars is as productive of oxygen as Antarctic ice covered lakes - and even if all that oxygen ends up in the atmosphere, the signal from all of that photosynthetic life would still be lost in the noise and not noticeable in the atmosphere (I made it about 0.0002%, in a very rough calculation, by just assuming a residence time of oxygen in the Mars atmosphere of 4500 years, the same as for Earth - at any rate it would be a tiny, surely undetectable, signal).

Why Mars Surface Life May Leave No Traces In Its Atmosphere: Our Rovers May Need To Go Up Close To See It

also my Our Spacecraft Could Look Straight At an Extraterrestrial Microbe - And Not See a Thing!

Value of a non confrontational approach

You might think, why not go out and out, confront the issue head on, and whoever wins the confrontation gets the prize? Well, yes, sometimes confrontation can be good. Sometimes you have to do it. Or sometimes it's good to tackle an issue head on and you get more clarity from clearly exposing your differences from another person. If you are lucky, you may find that something new comes up that transcends either of your views or the things you knew, which you could only get to by clearly exposing the differences. Or you might be able to go different ways after the confrontation, with a bit more clarity. But sometimes you are "in it" together and can't just continue your separate ways, and sometimes after battling away at a confrontation, you find it is going nowhere.

At other times, you can compromise, find an approach that lets you accommodate both views at once to some extent. But sometimes a compromise satisfies nobody. It would satisfy nobody to pass a compromise law to let fruit importers import Hawaiian fruit into California on the first day of each month. The fruit importers would be severely restricted in what they can do, and every month there would be new opportunities for crop infestations by the oriental fruitfly, so the law wouldn't be much help to the fruit growers.

Sometimes then, confrontation isn't wise, as it only entrenches views, and it makes it harder to look at the good points of what the other person is saying. And sometimes compromise is impossible because it is a situation that just doesn't have a natural compromise that would satisfy both. When that happens, it's time to look for a non confrontational approach, a way ahead that while accepting the differences of views, leads maybe in an unexpected direction or in some way just takes a detour around the confrontation that was looming up. That can then be satisfactory to both.

That is what I'm attempting here. I think it's a situation where direct confrontation will only polarize positions and entrench ideas, I don't myself think that the compromise approach of sending humans to Mars with some extra precautions is adequate (highlighted by the problem of a human crash on Mars which would effectively end all possibility of planetary protection). But I do think it's a situation where a non confrontational approach is possible, satisfactory for both. That can give us some breathing space, which can lead to new ideas, discoveries and solutions for the way forward in the future, whatever it is.

Moving your house to avoid a pond for great crested newts

So, to try to see this in perspective, first lets try to look at something much smaller. Suppose you want to build a house and need to fill in a pond. You get an assessment done, and you are told that this pond is the breeding ground of a rare form of amphibian. In the UK it could be the great crested newt.

You might not give it a second glance, but this is a European protected species. Your would not be permitted to just build on its pond, but would have to preserve the pond and build somewhere else.

Of course some people couldn't care less about whether it goes extinct. But others do, and it's accepted, that we have to have laws like this to protect endangered species. It's not a big deal if you don't care for great crested newts. You accept that others do, so you just build somewhere else. I gave the example also of the oriental fruit fly which makes fruit unfit to eat and so you can't import some fruit and flowers into California from Hawaii. It's an annoyance I'm sure for fruit importers, but it is something they understand the need for, and so most will just keep to the regulations.

For another example, the Kakapo, a flightless parrot, is very trusting and vulnerable to cats, dogs, etc.

I think most people would understand and accept that you can't have cats and dogs on islands inhabited by the Kakapo. And similarly it's easy to understand why you wouldn't be able to get permission to melt through the ice above the Vostok lake in Antarctica to put a human occupied submersible into it and cruise around. That's perhaps the closest to Mars planetary protection, because there, the aim is to keep microbes from the surface out of the lake.

What if there seems to be no alternative? - we must have Mars!

But where it gets much harder to cope with is if there seems to be no alternative. The Mars colonization enthusiasts want to colonize Mars. If the planetary protection rules were enforced as strictly for humans, as they are for robots, it would certainly keep humans away from Mars altogether. I think everyone would agree with that much. There is just no way you can sterilize a human occupied lander to robotic standards, because of the trillions of microbes that live in and on the human body, also in our food, and in the air.

Also, if you assessed human landings on Mars in the same way you do for a robotic mission, you'd have to do planetary protection assessments of the effects of a "hard landing", i.e. a crash on Mars, as I looked at in this booklet:

Can We Risk Microbes From Human Crashes - On Mars? If Not, What Happens To Dreams To Colonize The Planet?

The only way humans could be permitted to go to Mars surface under COSPAR recommendations in the near future would be if they had a consultation that reduced the planetary protection requirements to much less than that needed for robotic spacecraft. Also they would have to just choose not to investigate the effects of a crash of a human spacecraft on Mars (because that would count as an immediate fail of planetary protection). And if a human occupied spacecraft did crash on Mars, I think that would pretty much be the end of planetary protection for Mars.

The result seems inescapable to me -, if humans go to the Mars surface, we would probably have to relax the requirement of biological reversibility. Even if the microbes did not encounter any habitats on Mars, the spores would be spread over the surface in the dust, and it would probably be impossible to "put the genie back in the bottle".

Spores last for a long time, especially if they can get into a shadow, protected from UV light, and even more so if they get into a cave. They can sometimes last for millions of years on Earth. Eventually, in the global dust storms, some of those spores would encounter habitats, if there are any at all on Mars. They'd still be there thousands of years in the future also, to potentially cause problems with plans to transform Mars. For instance, if we try to roll back to early Mars, or to do step by step terraforming, or other transformations based on introducing some species before others (ecopoesis), these pesky spores could scupper all our plans.

It would still not be a confrontation if you could land humans somewhere on Mars isolated from everywhere else. But the Martian dust storms turn the whole planet into one connected system, apart from a few places perhaps, like the crater at the summit of Olympus Mons (on short timescales of thousands of years anyway, so long as it doesn't erupt). And even if you aim for the crater at the top of Olympus Mons, there's a possibility that the spacecraft crashes somewhere else on Mars during the landing attempt. And it might not be totally isolated even at that height surrounded by the rim of the crater.

Ponds and flightless parrots again - back to the Moon

So - it's like the example of the island of the flightless parrots, the Kakapos, or the pond for the great crested newts, except that it is now a planet sized "pond", and a planet that some humans want to attempt to colonize. And there seems to be nowhere on Mars that would be truly isolated.

Anyway - this becomes a confrontation when you think there is no way ahead. If you can just move your house to avoid the pond with the great crested newts, no problem. So that's when I realized, that what is needed is an alternative vision, somewhere else in the solar system that is as good as Mars. You can use the asteroids, and Phobos and Deimos for materials to build habitats, and some space advocates are very enthusiastic about such ideas. But for others similarly minded to Elon Musk, the asteroids don't quite cut it. Mars may seem a lot easier in some ways than building habitats from asteroids. At any rate, it may seem a rather different direction of space settlement, a different kind of vision.

But what about the Moon? Could that help defuse the situation? I was already a "Moon firster" and was aware of some of the material on the subject. But until I wrote this book, as I've said, I had no idea quite how many points there were in favour of the Moon as a place for human habitats and ISRU. Depending on what we find when we explore, study and prospect further, the Moon might actually be better than Mars for this. So - like the house builder moving the position of their house to deal with the issue of the great crested newt pond - is it possible that the Mars enthusiasts can move their base to the Moon, and use much of the same ideas for ISRU there, instead? For the first few missions at least?

Meanwhile also of course, we would explore Mars, and eventually send humans there, to explore it from orbit. We can also use many of the ideas for Mars Direct, and other Mars architectures to send robots to the surface - highly capable fast moving rovers fueled by the methane fuel that are used for humans in those designs. Similarly, use the Mars stationary satellites over the base to relay signals back to Earth via broadband.

In this way we can get some breathing space, of a few decades, hopefully, to find out about Mars on a scientific level. To find out if there are habitats there for Earth life and search for exobiology. Meanwhile, you are also building up an infrastructure on Mars and in Mars orbit that would be useful if we did ever decide to send humans to Mars. Or indeed, it could be useful for other things too, anything we might do on Mars. Perhaps you decide to try ecopoesis (duplicate the biological transformations of early Earth on much faster timescales), or turn the clock back to early Mars, or transform it in some other way, or even grow plants there (plants could be grown on Mars using sterile hydroponics without impacting on any native Mars life, since seeds can be sterilized). There would be many possible futures still open to you at that point.

Also meanwhile we can work on space habitats, closed systems, eventually build city domes on the Moon and large closed systems in the lunar caves, continue to explore ideas for creating larger and larger self sustaining habitats. Whether we eventually get to the point of terraforming entire planets, I think can be left to later, until we have much more understanding than we have now, with these early experiments. So, then it becomes an open path, where instead of closing off futures, we open out to more and more possible futures, and wider vistas at every step. These vistas don't just include Mars either but many destinations for humans in the solar system.

If this approach is valid, I'm sure it will still be a slow process. People don't change their ideas overnight, especially if they have been working for decades to try to get humans to Mars. And this is just one vision, which has to be part of a debate, to explore possibilities. But I hope perhaps that with this book I'm helping provide a greater diversity of visions for the future. :).

How many years are needed to do a biological survey of Mars?

This is a bit like asking how long a bit of string is. The surface of Mars is similar in area to the land area of Earth. If you had a couple of missions each to each of the Earth's main continents, how much would you learn about the makeup of Earth at ground level?

However, to make a start on it, Carl Sagan had to come up with a number of biological exploration missions, for one of his calculations. Writing in the mid 1960s, he assumed that about 60 missions to the Mars surface would occur before a human landing, giving enough time to get a first idea of the exobiology of Mars. He assumed 54 of those successful, and 30 flybys or orbiters, in a twenty year exploration phase before a human landing. So that's averaging nine missions for every opportunity to send spacecraft to Mars (See his "Decontamination Standards for Martian exploration programs").

So far we've had seven successful landers in the six decades since he wrote that: the two Viking spacecraft, the Mars Pathfinder lander (with its tiny Sojourner rover), Spirit, Opportunity, Phoenix and Curiosity. Of those seven, we have three landers able to travel kilometers, the Spirit, Opportunity and Curiosity rovers, and one tiny rover able to travel of the order of meters, the Sojourner rover. In addition, we've had 13 successful orbiters if I counted it right. And we have one extra lander and one orbiter on the way there right now (the ExoMars Trace Gas Orbiter and the Schiaperelli lander which is mainly just a technology demo and test for ExoMars, only able to survive a few days on the surface).

However, only two of those missions could really count as biological exploration - the two Viking missions. I think you could call the Trace Gas Orbiter, and Curiosity early stage pre-biological exploration missions. They could in principle discover life, but both would need a strong signal to have a chance to distinguish it from non life easily.

So that's only 4 missions so far with a strong biological focus: two stationary landers, one rover, and one orbiter. And only the Viking landers are really strongly focused on in situ life detection. You could say that Carl Sagan's planned "biological exploration phase " really started and then stopped immediately with the two Viking spacecraft. We have done no direct life detection tests on Mars since then, so I'm not sure if you can really include any of the missions since then as part of his biological exploration phase.

ExoMars in 2020 will probably be the first mission to be able to search for present day life in situ on Mars to some extent, and still is not as sensitive for this task as Viking was designed to be (with controversy of course about whether it discovered anything because of the unusual Mars chemistry). And even with ExoMars, its main focus is past life, with its search for present day life as a bonus. The area it's going to is not high on the list of candidates for present day life.

That's mainly because for about thirty years, most scientists thought that present day surface life on Mars was impossible. This is now changing, and on the plus side, our tools for investigating it have moved forwards by leaps and bounds since Carl Sagan's time, but the habitats on Mars have also turned out to be much more elusive than Carl Sagan could have imagined.

So I think we have to say that the biological search on Mars is just restarting, after a long pause after Viking in the 1970s. So, to venture a very rough guess, just based on Carl Sagan's numbers, it's at least a few more decades required. If we send, say, a couple of new landers for each launch opportunity, it would be 54 years to complete his preliminary survey, unless Mars exploration is stepped up hugely. If we can get it up to the levels envisioned by Carl Sagan or further, perhaps ten or more missions every two years, maybe we can do it in twenty years or less. Though, of course, in the other direction, if there is present day life on Mars, we might find it with the first mission to go to a promising habitat there. You never know.

Speeding the search up with miniature robots - what could we do if we had funding for a prelminary exobiological survey of the whole of Mars from earth?

Miniaturization may speed it up also, if we can scatter lots of smaller robots over the surface of Mars. See my Soaring, Buzzing, Floating, Hopping, Crawling And Inflatable Mars Rovers - Suggestions For UAE Mars Lander.

However, a swarm of 54 identical probes all sent to explore a single cave or a single region on Mars, and 30 identical orbiters similarly wouldn't hack it. Also, Sagan was thinking surely of missions with capability similar to Viking, so several instruments and very sensitive. We can certainly do with a lot less mass than Viking, today, and maybe we could get dozens of landers into a single launch of something like the Falcon Heavy, but they need to be carefully planned missions.

Imagine trying to get a clear view of the biological diversity of Earth with 54 landers, so about eight per continent, or in terms of countries, one lander for every three countries. When you think about it that way, it's not a lot to try to find out about a planet with a total land area similar to Earth, and with a complex and diverse geology.

There are many places we need to explore and dedicated missions for each. But if small, many of them could go on the same launch perhaps, then sent to many different locations on Mars from a mother spacecraft in orbit around the planet. Perhaps it could even send later missions in response to results of earlier ones.

This is a survey I did of some of the proposed surface habitats on Mars as well as some of the near surface ones. Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,... which may give an idea of the variety of possible surface habitats that have been suggested, most of them new suggestions in the last decade or so, and of course, the RSLs now confirmed to have liquid water (almost certainly) though not yet settled whether they are habitable or not.

So, what could we do if the funding was available to do an exobiological survey of Mars from Earth? I'd think you need a few missions to each of these targets myself:

  • The Recursive Slope Lineae (RSLs). You would need to send missions to more than one of those as they are especially interesting, geographically isolated and it's possible some have life and some don't.
  • The flow like features in Richardson's crater near the south pole. This may consist of fresh water trapped under ice, so are especially interesting for viability
  • Equatorial sand dunes. Levin thinks Viking discovered life already, and recently with discovery of circadian rhythms in the re analysed experimental data, others think there is a possibility of that also. Then, whether Viking found life or not, there are ways they could be habitable. So we need to check up on that to be sure. Also Curiosity found a liquid water layer a few cms below the surface of the sand dunes indirectly. Nilton Renno has suggested that microbes could find a way to create a niche in it, by transforming the environment as it can do on Earth even though the data suggests it is always either too salty or too cold for life. [ExoMars may give the first ideas about this - though it's not quite as sensitive as Viking's labeled release, it could find life in the Atacama desert core which Curiosity couldn't]
  • Salt / ice interfaces. Nilton Renno's "swimming pools for microbes" in droplets of water that form where salt touches ice.
  • Salt pillars and salt deposits, for deliquescing salts, and for water that can form in fine pores in salt pillars.
  • Both of those could be combined with a visit back to Phoenix's landing site - a study from ground level there able to detect life could also detect whether any of the Earth microbes from Phoenix have been able to replicate as Phoenix was crushed. Hopefully not, but if they have best to know at an early stage. And gives us some ground truth for robotic exploration sterilization to show our measures are adequate.
  • The Hellas basin because of the icy mists that form there and because it is the densest atmosphere on Mars which could make a difference to habitability.
  • Caves need a visit. Not so much lava tube caves as other types of caves, for instance ones formed by slippage, or ones that formed through erosion by water or dry ice. The difficulty is, they are hard to spot form orbit. We do need survey not just orbital images, which are also limited to particular times of day and such like. E.g. miniature planes to fly along the Valles Marineres to photograph it up close.
  • We should explore the surface itself for life, for lichens and cyanobacteria that might be able to grow in partial shade, using just the night time humidity, according to the DLR experiments.
  • Study the Martian dust as it might have spores in it from anywhere on Mars.
  • Check the polar ice caps for deep subsurface water, using radar, and if any is found, to drill down to search for life (if liquid water forms at depths of over 900 meters after a meteorite impact or through geothermal heating, it will remain liquid indefinitely through the flow of heat from Mars itself insulated by the ice above).

There may be other places to target, but those are the main ones I can think of right away.

The orbiters would be like the Trace Gas Orbiter, searching for traces of gases produced by life on Mars as well as photographing the surface. For instance our photographs of the RSLs from orbit are all taken in early afternoon, the very worst time to spot effects of liquid water on Mars. That's because the spacecraft that takes those photographs is in an orbit that takes it closest to Mars when locally it's early afternoon there. We need orbiters to photograph Mars close up at other times of day such as early morning. We also need orbiters dedicated to broadband communications with Earth (probably doing their own observations of Mars as well). These would certainly be in place for human missions for Mars, best done right away at the biological survey stage.

With broadband communications, then instead of communicating with Mars once a day as is the current situation you have delays of between 8 minutes and 48 minutes there and back. So, between 15 and 90 times a day, or if you have powerful lights and are fully powered at night, between 30 and 180 times a day. When Mars is closest to Earth then with broadband you could do as much communication and control in one day as we currently do in a year. Or even more if you use artificial real time.

There would be some building on previous expeditions so I think you definitely can't do it all in one mission. You'd have survey missions and preliminary missions first, but if we had the funding, say a dozen missions every two years for twelve years :). Each wave of missions building on the previous ones, refining the search. Or some other combination including maybe building up to more and more missions as we get an idea of which places to target.

You'd also be looking for habitats with no life. If there are surface habitats, whether there is life in them or not, those are vulnerable to Earth microbes meaning that sending microbes there is irreversible so you want to know that too even if they are uninhabited. They could be of great interest for exobiology indeed, especially if they have complex organics, but no life, or "almost life". So it is specifically a search for present day surface habitats and life - or ones that are reasonably easily accessible from the surface.

If it's possible to get humans to Mars orbit, then they could oversee all these rovers on the surface, rather similarly to the game of Civilization. Many of those 54 landers would be doing routine tasks at any time, things they can do autonomously. They could be controlled remotely from Earth using broadband. But from time to time they'd be doing something more challenging and interesting and that's where astronauts in orbit would step in. So in that way, a half dozen astronauts in orbit could work with all of those 54 landers and more using telepresence.

For more about the potential habitats, see my Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,...

A rapid survey of Mars does seem possible - however none yet planned to guide our decisions by the 2020s

So, it's possible we could survey Mars more rapidly, but there aren't any planned missions yet to suggest we are going to do this in the very near future, as in, the next decade (say).

In the circumstances, if we send humans to Mars in the 2020s or in the 2030s, unless there is some big change, and someone does a large number of robotic missions first, we can't have anything like enough information by then to know what effect their microbes would have on Mars.

If you share Elon Musk's certainty that there is no life on the surface - which to be fair was the scientific consensus right up to 2008, then you may agree with his conclusions there. But ideas about Mars are changing fast, and we can't be so sure now about the apparent certainties of the early 2000s.

Clash and confrontation?

For this reason, I foresee a possibility of some kind of a confrontation, where experts who meet to make planetary protection guidelines for COSPAR just don't have enough information to say for sure if there is present day life or habitats for Earth life on Mars or not. So then it would come down to personal judgement. Experts who are skeptical about life on Mars might say to the Mars colonist advocates like Elon Musk, "Sure, go ahead, you probably won't do any harm". While those who are optimistic about the proposed habitats are quite likely to say "Slow down, we need more data". I wouldn't be surprised if the workshop was inconclusive with some saying it is okay and others saying it is not.

This potential confrontation was highlighted recently in my guest appearance on David Livingston's "The Spaceshow" on 3rd May 2016. I said, during the show, that it's possible that we might not have enough information for COSPAR to approve humans to Mars soon enough for Musk's plans, and also said that it is still a possibility that we could find out that there is vulnerable life on Mars. I was saying much the same things I've been saying in this book.

Anyway I expected this to be a controversial thing to say, knowing that many keen Mars advocates would be listening to the program - but I was surprised at quite how controversial it seemed. From the questions we got by email, it seems that many people would be very upset if their plans to attempt to colonize Mars were even delayed a few years because of issues such as this. David said that the possibility that planetary protection issues could delay their plans is never raised in the Mars colonization conferences at all, which are held every year in the States. So, if I'm right about this projection, it would be a great surprise and shock for them. What can we do to help defuse and resolve this possible future confrontation? My Case for Moon First book actually came out of my deliberations after thinking over that show.

This approach doesn't mean that humans can never land on Mars ever

The idea isn't at all to prohibit humans on Mars. The humans are not the problem; it's only their microbes that are. And the idea is to do it step by step and to make sure we understand Mars and understand the implications of our actions before making a decision about whether it is okay to have human boots on Mars.

I'm a spaceflight and science fiction enthusiast myself and I'd love to be able to cheer on humans on an expedition to Mars. Just for the childlike wonder of seeing humans doing things like that in space. So it would be fun to see humans go to Mars. And at least we can send them to Mars orbit whatever we might discover about the surface - so long as it is done with care to make sure that they can't crash on Mars.

What about humans on Mars later on?

We could decide what to do later on, based on what we find out. If we find that there is some vulnerable early RNA based life on Mars for instance, I think that public opinion might well swing in the direction of saying we need to go slow here, and study it first before doing anything that could make it extinct on Mars. The scientists would be on the TV talking about how exciting it is, and I think nearly everyone would soon understand the importance of what we had found.

In the other direction, there might be other findings that show that microbes would have minimal impact on Mars. For one example, suppose that none of the proposed habitats turn out to be habitable for Earth life? I think that's an unlikely scenario myself, and it would be a disappointment for exobiologists, but it's a possible future as of writing this.

Or maybe new technology gives us the capability to send humans to Mars in a biologically reversible way. Again, it's hard to see that with present day technology, at least not for an interesting mission for the humans involved. But the human in a metal sphere idea shows that it is at least possible in a minimal rather uninteresting way.

Could there be some other more flexible and more interesting ways to achieve the same thing? I can't imagine how that would happen but there are many technologies today that I couldn't have imagined in the 1960s when I watched the Apollo landing on the moon on TV as a child of 14. Indeed right up to not long before the landing, the science fiction writers never imagined that it would be watched on global TV as it happened. So sometimes your ideas about the future can be upturned like that, suddenly, in just a couple of years.

If you have any other ideas for biologically reversible human exploration of Mars, do share in the comments!

When will we know enough about Mars?

I don't think we can answer this at this stage in any definitive way. It's asking us to predict future science. You can't know what direction it will go and what we will learn about Mars. So it can't be timetabled. Carl Sagan's 60 rover missions and 30 orbiters searching for life, mentioned above, was just for the sake of having a number to work with for his probability estimates.

Let's take it step by step, and send humans to the Moon and asteroids and Mars orbit first, and make the next decision based on what we find out from that first phase. The main thing right now should be not to close off future possibilities. If we make that decision in the future, it will be an informed decision.

We wouldn't know Mars completely, as that would take for ever. We don't understand Earth completely yet. But we'd know a lot more about Mars than we do today. We need to leave it to our future selves or descendants to evaluate what they know then, and to decide whether they know enough yet to make this decision. I think that with the rapid pace of science, you can only foresee the future perhaps ten or twenty years ahead in detail, and even on that timescale, surprises are likely.

Two futures - humans landing on Mars or a habitable Mars surface with humans in orbit only

I see two possible futures here. One, where we find that the Mars surface is uninhabitable and humans land there just as they did on the Moon. That would be fun and exciting just as it was for the Moon. The young space geek, science fiction loving kid in me would just love that!

In this future, humans could perhaps land early on - though there are still issues to think over about introducing earth microbial spores that could interfere with future plans to transform Mars. It is after all, an entire planet, connected through the dust storms, and the dust able to protect spores from UV light. Also, after the initial excitement, it might well turn into a place like any other with humans cramped in habitats, complaining about food and the difficulties of being cut off from Earth, sending video clips talking about how they never get to see a blue sky or sunlight or trees or grass any more, saying how homesick they are, and how they can't get out of their habitat - I'm sure there'd be some grumbling from people who didn't realize quite what they are getting into. It might not be as glamorous as it seems in advance.

The other future is one where the Mars surface turns out to be habitable. In the most exciting future here, perhaps nearly all those suggested habitats turn out to be habitable. Nilton Renno's salt / ice interfaces, the seeps of briny water, the pure water at 0 C in Richardson crater due to solid state greenhouse effect through pure ice, and on the surface using the 100% night time humidity, all of those inhabitable.

Almost anything that could happen in this future is exciting. Even Zubrin's picture of a Mars with the same lifeforms as Earth would be exciting, how could that possibly happen? How did they all get there, and when, and why didn't they evolve in some different direction from their cousins on Earth? The future of uninhabited habitats would be interesting too. We'd learn a lot from both these futures.

The most thrilling future of all here, though, would be the discovery of indigenous life or early life precursors. Like the possible life forms in ALH84001, with the debate going both ways about whether it is life or not. Mars has such a different past from Earth, at its most habitable for just a few hundred million years, with oceans, early life could have evolved there and still be there. Those early life forms might never have gone extinct on Mars. That would be the most exciting of all, life that was made extinct on Earth, and they could be extremely vulnerable to Earth life. That would fill in a huge gap in our understanding of life.

Either an early form of life on Mars, or some form of life that's followed a totally different direction of evolution from Earth life. Even perhaps more than one form of biology, different directions explored and perhaps none of them have yet taken over as the only form of biology on Mars.

That would be like discovering an exoplanet, complete with its own extraterrestrial life, in our own solar system. Ok, humans can't land on the planet, not early on anyway. But to compensate, they can explore it by telepresence, and we can all participate, looking at the streaming feeds from Mars and walking via virtual reality through the landscapes they uncover in their explorations from orbit. It would be exciting to follow the expeditions of the telenauts exploring Mars from orbit. And there's something also fascinating about a place you can't go to in person, for whatever reason. It would add to the interest and mystique of Mars.

For me, that's by far the most exciting future here. So I'm rooting for that future where the habitats turn out to be inhabited - and most exciting of all, a future with some form of indigenous life, early or life precursors or alternative biology. This is a scientific possibility at present, something that could turn out to be true. I hope this is what we'll discover on Mars in our near future.

There might be other possibilities that we can't see yet. I hope we don't end up in a future where we accidentally introduce Earth life to Mars however. That would be so sad, to do that by mistake, if that's not what we want to do.

Only one Mars - no warp drive yet

These planetary protection issues arise so acutely for us because there is only one Mars within reach.

  • If Mars has early pre-DNA life on it, then for all we know, it may be the only place in our entire solar system with early life on it.
  • Or if for instance Europa or Enceladus also have early pre-DNA life, Mars could be the only terrestrial planet with this form of life in our solar system.
  • If there are habitats there, but no life, again it is the only terrestrial planet in our solar system which is habitable at all on its surface and has no life on it, a situation that could teach us a lot about the role of life in planetary processes as well as help us distinguish exoplanets with and without life.
  • If it has complex life precursors but no life, again it is the only terrestrial planet in our solar system like that.

And so on for all the other various possibilities for what we may find there. Mars is our only opportunity to study a terrestrial planet of that type. And because we can't travel outside of our solar system easily then this means it is the only terrestrial planet of its type in the habitable zone of its star in the entire universe that is accessible to us to study close up.

If we could travel at warp speed to distant star systems within days or week, maybe we might know of thousands of Mars like planets with pre-DNA life, or whatever it is that makes Mars unique in our solar system. Then, it might perhaps be a matter of less consequence what we do to Mars. We could try experiments then with some of those many planets.

Even then I think we have a fair bit of responsibility for those planets. Even though we would have many planets at our disposal, it would be an irreversible change, still for any of them. We'd have responsibility for the future beings that might evolve on those planets which we transform, maybe millions of years into the future. We'd have to think through whether they would be able to keep their planet habitable in the long term future, especially future intelligent lifeforms that may arise there which we may not even be able to predict at present. For instance, to start a new habitable planet that would unterraform a few thousand or a few million years into the future might well be seen as irresponsible even if we have thousands of planets at our disposal to experiment with. We might still have some kind of a "prime directive" that applies even to planets with only primitive life.

But - it would be a different situation. We would still have ethical dilemmas and responsibilities, but we wouldn't have so much to lose by transforming the planet. As it is though, we have only the one Mars in our solar system, just as we have only the one Earth.

There is no immediate prospect of developing a realistic warp drive as far as we know, ideas yes but nothing concrete. There are issues with warp drives also as if it is possible, it may permit travel backwards in time which is an idea that challenges causality. Faster than light travel is common in science fiction, but though we do have theoretical possibilities for it in our own universe already, such as the Alcubierre drive, this requires exotic matter with negative energy which we don't know how to make. It's not yet at all clear that we will ever be able to do it in practice. Certainly we have not got any spacecraft able to do this yet, and I don't think many would say we should plan on the assumption that we will be able to do this in the near future.

So we need to proceed carefully with actions that may change Mars irreversibly. We may never be able to access another planet like this, within a travel distance less than decades even traveling at a tenth of the speed of light.

Even in future if we ever do develop a warp drive, it may still be unique. It might be that only Mars has early life that's related in some way to Earth life, to give some example (the hypothesis that Earth life originated on Mars first). There may be many other such connections, including just that it is a planet of exactly the same age (to within a few million years) around the same sun and with a shared history.

Other planets may have other forms of early life in other solar systems but that close connection to Earth could make Mars of especial interest to us. That's just one example. It's not impossible that Mars, and Earth are unique in various ways in the entire galaxy. Also, on the knowledge we have so far, it's not impossible that our solar system is the only solar system that has life in it in the entire galaxy.

So one way or another, Mars could be unique and very precious to us, as the only planet of its type accessible to us, right now, and quite possibly also for many or all future civilizations that arise on Earth in the future.

Precautionary principle and super positive outcomes

The main principle here is that we should advance by increases of knowledge until we have know enough to make informed decisions. And for as long as we have fundamental gaps in our understanding,with significant unanswered questions about whether this course of action could cause problems for us and our children and future civilizations on Earth, we just shouldn't introduce Earth life to Mars irreversibly, or indeed, to anywhere else in our solar system.

Colonization advocates will often argue that since we don't know that we will cause problems on Mars, we might as well just go ahead and see what happens, and "learn on the job" what impact we will have on Mars. But for me that's not nearly good enough reasoning to back up an action that risks potentially irreversibly introducing Earth life to Mars. This section comes out of attempts to make this clearer, and to explain why I think it is so important that we don't proceed here out of ignorance, but make sure we have a reasonably clear understanding of our situation first.

It's similar to the Precautionary principle guideline in International Law

"When an activity raises threats of harm to human health or the environment, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically.

"In this context the proponent of an activity, rather than the public, should bear the burden of proof.

"The process of applying the Precautionary Principle must be open, informed and democratic and must include potentially affected parties. It must also involve an examination of the full range of alternatives, including no action."

My suggestion for a new principle here is based on the idea of a "super positive outcome" - a potential but not certain outcome which could have transformative effects on us, our children and all future generations and civilizations. In this case discovering some alternative form of life or early life on Mars could revolutionize biology, could potentially benefit medicine, agriculture, and indeed anything that we do that uses products of life, also nanotechnology. It could potentially, in the best case scenario be a hugely positive transformative discovery.

The precautionary principle can't be applied here, if we start an irreversible process that makes some unique or early form of life extinct on Mars .There is no risk of harm to human health and the environment, at least not on Earth. But there's a risk of destroying a potential future benefit of immense value. The consequences would be so positive if it exists, and it would be so tragic if we found that there was something unique like that on Mars right up to the first human landing or crash on Mars, and that we made it extinct. And as with the precautionary principle, there may be no way we can establish the cause and effect relationships thoroughly before it happens. We don't even know what the possible effects are until we find out whether Mars has habitats and whether those habitats contain life.

I suggest we should have similar guidelines for super positive outcomes like this - things of potentially overwhelming positive value that we could discover:

"When an activity impacts on a potential super positive outcome, precautionary measures should be taken even if some cause and effect relationships are not fully established scientifically.

"In this context the proponent of an activity, rather than the public, should bear the burden of proof.

"The process of applying the Precautionary Principle must be open, informed and democratic and must include potentially affected parties. It must also involve an examination of the full range of alternatives, including no action."

So I'm not saying we should never land there. But that if we do, then as with the precautionary principle, it has to be on the basis of knowing clearly the consequences of our actions, with public debate and open and informed democratic discussion of whether we should do it.

But to have informed public discussion, first we have to know what is there. For that we need to explore and discover first, before making any irreversible decisions such as whether to introduce Earth life to a planet.

For more about this see my "Super Positive" Outcomes For Search For Life In Hidden Extra Terrestrial Oceans Of Europa And Enceladus

For discussion of how we could explore Mars first, in detail, see my section How many years are needed to do a biological survey of Mars? (above)

Searching for life on Europa and Enceladus

The main focus of this book is on the search for life on Mars. However, many of the same ideas apply to searches for life on Europa and Enceladus, and in the other direction too, with Europa and Enceladus, we have a chance to start from scratch and design new ways to search for life, learning from our experiences on Mars. Perhaps we can find a way to do it which doesn't need us to do these probability calculations such as Sagan did for Mars. Can it be possible to search for life in a 100% safe way with no risk of contaminating the places we study at all? And if so, can this perhaps be applied to Mars too, for future searches of the present day habitats on Mars?

The life searches to Europa and Enceladus will be especially challenging, because the target is ice. When ice is melted, life can survive there readily. But some of the targets on Mars, such as the flow like features in Richardson crater, may be similar. They are like tiny cm thick subsurface oceans. Maybe we need to use similar care in our search for life there as we need for Europa and Enceladus.

Hubble's confirmation of probable geyser activity on Europa

Hubble has found new evidence of possible plume activity on Europa. In a series of ten observations, they saw them on three occasions. Here are the images they created.

The possible plumes are in the seven o'clock position, not far from the South pole - though the central image here has another possible plume that's close to the equator.

Interestingly, they spotted them in the same position as the previous plume detection in 2012:

Hubble Sees Evidence of Water Vapor at Jupiter Moon

Note that in all these images, the photograph of Europa was not taken by Hubble. It just made the observation of the water plume - those large blue pixels in this last image. 

Europa is tidally locked to Jupiter, so every time Europa does a transit of Jupiter, we see the same face of it in the same orientation. This shows how it works:

So this could well be a recurring plume in the same place as for the 2012 observations.

This is potentially exciting news because the last time it spotted a plume of water, it seemed to be a once off observation and didn’t get repeated. After the initial excitement many astronomers concluded it was probably just a rare asteroid impact on Europa sending water up into space. Europa's Elusive Water Plume Paints Grim Picture For Life - Astrobiology Magazine

Now that Hubble has spotted it again, this makes asteroid impact a very unlikely explanation, especially as it's been observed in the same position approximately, multiple times. This suggests that it is probably a huge geyser. This is  very exciting news for astrobiologists, because such a huge geyser would suggest the water is coming from deep below the surface, maybe even indirectly or directly from the subsurface ocean 100 km below the surface. This image shows some of the possibilities.

In the case of Enceladus we have evidence that suggests that the material that Cassini observed was perhaps even in contact with hot rocks only a few months before the observations. However the ice cover for Europa is 100 kilometers which makes it rather difficult for tidal effects to keep a channel open all the way down to the subsurface ocean against the immense pressures of the ice closing the channel.

This seems a more likely scenario

There a hot plume of water from the ocean rises very slowly through the ice. We have evidence on the surface of chaotic terrain, which may be the result of one of these plumes reaching the surface. The water, denser than ice, would cause the surface of Europa to dip as it approached it, and then once it reached the surface, the water would freeze and break up into giant icebergs that would turn over and form the chaotic terrain. At least that's one explanation of how it might work. If so, these geysers could come from one of these giant rising hot plumes of liquid water.

This in turn is very interesting because this could make it one of our best chances in the solar system for finding extraterrestrial life and even possibly, complex multicellular life such as we have on Earth. There is almost no chance of life getting transferred from Earth to Europa or vice versa over the entire history of the solar system as models suggest that only a few meteorites have ever made that transition in the entire history of the solar system. And if the ocean material is indeed sent into space in a geyser, one of our spacecraft could sample it just by flying through it with no need for a lander.


How can we find out more?

NASA has plans for a Europa multiple flyby mission to be launched in 2022 on the SLS to get there in just 3 years. If you do a type II Hohmann transfer, spanning less than 180 degrees around the sun, then you can get from Earth to Jupiter in under two years as Voyager 2 did, taking one and a half years to reach Jupiter from Earth. So it is not a particularly long journey time from Earth.

Because of the strong radiation around Jupiter close to Europa, it actually makes most sense to do flybys of Europa rather than to orbit it. After each flyby, they will have plenty of time to send back the vast amounts of data they can collect with each close approach. The end result is much more data sent back and a mission that can last for years instead of just a month or two.

Keeping safe - sample geysers

I think the best solution here is to focus on sampling any geysers as our main priority. We can definitely do that with a mission to Enceladus, and now it seems we may be able to do it for Europa as well. Enceladus is less known amongst the general public, but it also may have life.

Geysers on Enceladus (moon of Saturn). A spacecraft could fly through these geysers (Cassini has done so many times now). It could do a detailed analysis and even a life search as according to some theories, the water in these geysers was in Enceladus’ ocean as recently as a few months before they are ejected into space. Europa may have geysers also but with its larger gravity they may not go so high into space, so may be harder to spot.

With these new observations this now becomes a top priority. As with Cassini for Enceladus, a Europa flyby mission should be able to do multiple flybys of Europa. Cassini found out a lot about Enceladus's subsurface ocean from analysing the plumes, and that is with scientific instruments built 20 years ago (it was launched in 1997) and a mission that was planned at a time that we didn't know that geysers were even a possibility. 

A flyby mission can go through the plumes at different heights, and at different times in the orbit and gradually build up a picture of what is in the material. It can actually sample the material directly and analyse it on board the spacecraft. The Europa flyby will do around 45 flybys of Europa so will have plenty of opportunities to fly through the plumes.

So then what about landing on Europa?

It’s actually quite a challenge to land on Europa. I’m not at all sure we should be doing it now even. Rather controversially, NASA have a mandate to include a lander on this mission. This is a possible version of it, see A Lander for NASA’s Europa Mission

It's controversial because this is an idea put forward by Congress. This is not usually how you plan science missions, that a politician tells you that you have to do it in a particular way. That's more like the way that human missions are done, where the objectives are often to a large part political. Normally it's a case of asking the scientific community for suggestions, then detailed proposals, fully worked out with costings, and then they are compared with each other based on their scientific merits rather than their political merits. It seems odd to do it the other way around, for a pure science mission. 

The original plan was to have both lander and orbiter on the same mission. Now Congress have mandated NASA to do them as separate missions, and have also said that both missions have to use the Space Launch System (SLS) - a heavy booster being developed in the States, which itself is rather controversial, since it is going to be high cost, it's going to fly infrequently, and each launch is going to be extremely expensive. It will be a remarkable vehicle able to send large masses into space and send human crew on deep space missions. However some think it will be overtaken by the private sector who have their own independent ideas for ways to achieve heavy lift such as the Falcon Heavy. The Europa mission could cost upwards of 2-3 billion dollars not including the launch, possibly as much as 3-4 billion dollars. The SLS launches themselves will add $500 million to $1 billion apiece just for the launch. The whole thing is quite controversial. See Two SLS to Jupiter in the Space Review.

Anyway this is now a very unique mission, one of the few to have a launch vehicle selected by congressional mandate. All this does have its advantages though for a Europa mission.

First, the spacecraft can be far more massive. It can have more instruments, a much shorter transit time to Jupiter of only three years, and it can have more radiation shielding to protect it from Jupiter's ionizing radiation. It can get there so quickly because with such a capable launcher, there is no need for a gravity assist.

For the orbiter, the main controversy would be about the cost. The mission itself will be much more capable than it could be without the SLS. 

However for the lander, then in the case of Europa, there are additional reasons why a lander makes it more tricky. The first issue is that the surface of Europa has not yet been imaged in the detail needed to choose a landing site, and is thought to be very rugged in detail. Landing on Europa might be as risky and fraught with unknown quantities as landing Philae on comet 67p, though for different reasons. There is no risk of it bouncing off the surface, but it could crash on rugged terrain.

Another issue is that you have to sterilize the lander sufficiently for planetary protection, because the very last thing we want for Europa is to go there just to discover life that we brought ourselves. Is that something we can actually do at this stage? It's a huge challenge when the target is icy. A hard landing (crash) on the Europan surface could heat the ice to melting point, or even potentially contact liquid water beneath thin ice and the ice could then shield microbes from the ionizing radiation of Jupiter.

The strange thing here is that congress actually have mandated a launch date for the lander too. NASA has to launch it in 2024. That means they have to send it to Europa a year before the orbiter gets there, and so before they have any new data on the Europan surface conditions.

So let's look in detail at some of the issues with sending a lander to Europa based only on the knowledge we have about it so far. Is it something that we can actually do, realistically, in this time frame - with a launch in 2024, and do we know enough to design it before detailed observations of Europa from the orbiter?

First, the surface is unknown at the scale of meters, most of it. As an example of how little we know, one theory that has not yet been disproved is that parts of the surface might be covered in closely spaced vertical “ice blades” or “ice knives” which would make a landing there hard to achieve. On Earth these blades form quickly, in special conditions On Europa they would take millions of years to form, but it’s the same basic process. As Daniel Hobley said: "Light coming in at a high angle will illuminate the sides of the blades, causing them to retreat away,"

These are called Penitentes. See Penitentes: Peculiar Spikey Snow Formation in the Andes

This video shows how they form on Earth and decline, time lapse:

Here is a photo from the European Southern Observatory site high in the Atacama desert:

Planetary Analogue, see also their Icy Penitents by Moonlight on Chajnantor, and Iconic, Conical Licancabur Watches Over Chajnantor

Ice knives on Europa

On Europa, if they exist, these structures can potentially be meter scale or higher. With no atmosphere, the conditions on Europa might well be ideal for their formation. Our missions to Europa so far haven’t taken high enough resolution photos to see them. Ice blades threaten Europa landing - BBC News

They wouldn’t be the result of ice or snow subliming into an atmosphere, obviously. It’s a slightly different process. Instead they’d be the result of the sunlight causing the ice to sublime to water vapour in a vacuum at very low temperatures well below 0 °C. Also they would form slowly over much longer timescales, of millions of years.

The surface of Europa is about 50 million years old, so when we ask if penitentes can form on Europa, one of the main questions is, how much can the ice there erode under the influence of sunlight in 50 million years? The answer to this question is extremely sensitive to the peak temperatures on Europa, to the extent that twenty degrees can make a difference between formations that are meter scale and ones that are on the scale of millimeters.

In the paper: HOW ROUGH IS THE SURFACE OF EUROPA AT LANDER SCALE? Hobley et al produce this table

So, for a surface temperature of 132 °K (about -150 °C) it loses about 5.66 meters over the average age of the surface of 50 million years. For a temperature of 128 °K (-154 °C) it loses 1.28 meters in 50 million years, tailing off to 1 cm at 116 °K (-166 °C), and only millimeters at 114 °K

So this is very sensitive to the peak surface temperatures of Europa. Also, the surface is eroded by sputtering from the Jupiter radiation and from bolide (meteorite) impacts. That would counteract the effects of the ice blade formation at temperatures of 126 °C downwards. They conclude in the paper that the knives could be from one meter to 10 centimeters in height, probably restricted to within 15 or 20 degrees of the equator.

However Europa also has “true polar wander” by which the entire crust moves over the subsurface ocean. This could reduce the size of the blades but also move the ice blades away from the equatorial regions.

Upturned icebergs - for regions like Thera Macula - amongst the most interesting regions on Europa

Other issues could include a frozen landscape consisting mainly of upturned icebergs. According to some ideas, then hot plumes of melted water rise from the deep subsurface sea and eventually reach the surface and produce these irregular landscapes, as icebergs form on the freezing surface, and then turn over.

One of the most interesting regions, thought to be most likely to have thin ice over liquid water by the “thin icers” is the Thera Macula

This might be a region of overturned icebergs with, perhaps, liquid water still present only a short distance below the surface. Most of these chaos regions are raised, which suggests the ice below them that lead to their formation has frozen. But Therea Macula is actually a dip in the surface of Europa which may be a sign that it has the denser melted water still beneath it. See Is Europa's ice thin or thick? At chaos terrain, it's both!

Possibility of liquid water close to the surface or breaking through

So there could also be liquid water close to the surface. Geysers are another possibility. So again there may be a small chance of our lander crashing through thin ice or a soft surface, especially if we land it on the most interesting regions such as Thera Macula. Or it could fall into a crevasse and be unable to communicate.

I know the plan is to orbit Europa for a while before the lander gets there, but what if the orbiter doesn’t find any suitable spot for the design of lander, and decides a different design of lander is needed, or no lander at all? Maybe the lander has to land somewhere uninteresting, or they have to hold back from landing at all for planetary protection reasons?

Can we sterilize a spacecraft 100%

Then the other problem is that we don’t know how to sterilize a spacecraft 100%. Or more accurately, we can sterilize a spacecraft completely, but the methods that do this, such as prolonged heat, or ionizing radiation, also destroy the electronics so it won’t work any more. That includes of course the ionizing effect of Jupiter’s radiation - although the surface of Europa is riddled with ionizing radiation that would quickly kill any human, any spacecraft there has to survive this, at least up to the landing, which would mean that it is protected sufficiently that microbes could survive also.

If there are some microbes on the lander, and they survive to the landing, then it might impact into liquid, or create a liquid area due to a crash on Europa which might be deep enough to shield microbes so they can reproduce there. Or microbial spores brought to Europa with the lander could eventually in the future over thousands or years find their way into the ocean.

Fast follow up landers

They plan to send the mission to Europa possibly as soon as 2022 to get there by 2025, using the SLS, which lets gets there, then our technology may be so advanced we can send a follow up orbiter or lander within months or a year or two. In any case I think we simply should not risk a lander at this stage due to planetary protection issues unless we can sterilize it 100%, or somehow can prove that there is no significant possibility of it irreversibly introducing Earth microbes to Europa. Even a 1 in 10,000 chance of contaminating Europa with Earth life, I think would be too high, given what we may be risking there, some unique discoveries that we could never do anywhere else. E.g. it could be some early form of life, not as far evolved as DNA or evolved in a different direction, which might be very vulnerable to DNA based life. And it’s probably impossible to do an accurate assessment of how likely it is that we could irreversibly introduce Earth life to Europa by mistake, we just don’t know enough yet about Europa or about exobiology with no examples yet of any known exobiology to base our decisions on.

Again by the 2030s we may have the technology to sterilize a spacecraft 100% without destroying the electronics. I hope so!

Mission to Enceladus geysers - and perhaps identical mission to Europa

Meanwhile one thing we can do right away is to send a mission to Enceladus to analyse its geysers close up, and it would be reasonable I think to send life detection instruments on that mission too. Instruments that would help with analysing whatever is in the particles, able to detect complex organics, and also able to find indications of life too if present.

If funding permitted, perhaps we could also send an identical orbiter geyser fly through mission to Europa “on spec” just in case we find geysers there, to save time. I think that would be less risky than a lander, no danger of crashing, and likely to add to our understanding of Europa even if it has no geysers, by examining the region around Europa just as Cassini did for Rhea etc.

There’s some evidence already of possible water plumes from Europa - though it’s a one off observation by Hubble which hasn’t been repeated. It might have just been a meteorite impact. If it is evidence of geysers, that could be very exciting for search for life on Europa. Water Plumes on Europa: What Lies Beneath?

In any case as I said, I think we should equip any Europa orbiter with similar instruments to Cassini which would help with analysing any dust or ice particles or gas around Europa with the capability of detecting complex organics, which may be in them whether or not Europa has life, and I think we should add chirality detection at a minimum. There’d surely be some dust or gas to analyse even if there are no plumes.

Safe and easy landings for Europa - “ice breaking” instead of “aerobraking”

Huygens was an easy experiment yes, for Titan. We can’t do aerobraking on Europa.

However you could do equally easy experiments for Europa - one idea is a penetrator, using what we could call "ice breaking" to slow it down. I'm not a fan of that myself for planetary protection reasons unless the penetrator can be sterilized 100%.

Planetary protection friendly version - artificial geyser - Bernd Dachwald’s idea

However there’s a planetary protection friendly version of it. You could use two spacecraft - a dumb penetrator consisting of just a metal slug, easily sterilized. This sends a plume of ice into space. You could use two “dumb penetrators” with the second one closely following the first for more effect.

In effect, you are creating an artificial geyser here. This would be followed by a low flying orbiter to capture the sample for analysis.

That would have minimal planetary protection issues if the dumb penetrators can be 100% sterile - e.g. just lumps of metal heated beforehand to temperatures where no Earth microbes could survive or otherwise 100% sterilized before impact. This is an idea Bernd Dachwald (head of the German IceMole project) once suggested to me in conversation, which I think is an interesting one.

However if Europa is indeed producing geysers naturally, we don't need to do this, we can just observe the plumes "as is".

Chipsats for Europa - could they be 100% sterilized?

Another interesting idea, here is an old mission idea to send “chipsats” to Europa’s surface, each one rather “dumb” but lots of them, each one consists of just a few sensors on a flat chip. Some would fail but enough would get through, and they would be able to survive impacts that a larger more complex lander couldn’t.

That sounds like a kind of a lander that is so minimal, perhaps it could be 100% sterilized by supercritical CO2 snow or something similar? That’s a technique that can remove all the organics from the surface of an electronics chip without damaging the chip. It’s been shown to work with USB drives. So though it might be tricky to scale up to a complete spacecraft, I wonder if it is good enough to 100% sterilize chipsats? It would have to be 100% reliable.

"ATTEMPT NO LANDING THERE" --New NASA Mission to Europa will Ignore Arthur C Clarke's Warning (2014 Most Popular)

Can we achieve 100% sterile electronics for a Europa or Mars lander?

There’s no in principle reason to prevent 100% sterile electronics. You just have to find some process that electronics can withstand and life can’t. If you heat metal to hundreds of degrees C for instance, no life will survive and the result will be 100% sterile. The problem is that this will destroy the spacecraft electronics too. So can we find a way to sterilize it of Earth microbes without destroying the delicate equipment? That’s the big question here.

Also all this might be far easier to do with a chipsat than with a large conventional spacecraft.

First one method being explored by the European Space Agency is Deep cleaning with carbon dioxide. and Science Daily article about it.

  • CO2 a liquid at 100 atmospheres and 50 C.
  • And then on release of pressure turns to snow and takes the dirt, organics, everything away leaving the surface dry.
  • Mixed with Hydrogen peroxide and other chemical to increase effectiveness.
  • Can be used even with sensitive electronics. Was used to clean usb drives in testing and they functioned afterwards.
  • Surface is left with no trace of organics, not just with dead micro-organisms. Major plus!

Could you remove all traces of organics from the exterior in this way? And - can you also keep exterior and interior separate so there is no chance of leaking contamination from inside the mole?

High temperature sterilization

Then also, if you can make the whole thing able to withstand high temperatures, you can just heat it up to a high enough temperature to sterilize all life.

The main issue with sterilizing modern spacecraft is that many instruments are quite delicate, also they can go out of alignment,so even the sterilization temperatures used for Viking of 111 °C for 40 hours is too much for them.

But there are electronic circuits now designed to operate at up to 200°C . High-Temperature Electronics

And there are other developments that should permit temperatures of 200°C upwards :).High-Temperature Electronics Operate at 300 degrees C | EE Times and Designing for extreme temperatures

There’s an economic incentive for developing these electronics, as they are useful in oil wells and motor cars.

I’ve never seen this suggested for a way to keep Europa landers sterile, but it sounds as if it should work!

Back to the drawing board probably for a lot of the designs to make the whole thing uses chips and solders etc that work up to high enough temperatures for 100% sterilization. But it seems like it may be possible! Thanks to Adeel Khan for the suggestion

Is this right? Is it possible to achieve 100% sterilization by heating electronics that’s capable of resisting temperatures of up to 300 C. I wonder if anyone working in the field of spacecraft sterilization has investigated this, either experimentally or in theory. Or is there some other way to achieve 100% sterile electronics such as the CO2 snow approach?

I think we need to look into that myself before we consider sending any probes to habitats that may include liquid water habitable to Earth life. Except of course for the plume flybys. They are safe so long as the ice particles they collect can’t dislodge microbe spores and return them to the liquid water in the subsurface oceans. That sounds likely to be for all practical purposes, zero risk though you’d need to examine it carefully of course.

Multiple methods at once

Perhaps for the best results both can be used one after the other. High temperature to make sure there is nothing viable. Then CO2 snow to remove the organics as far as possible. Heat it up again before it is released from the orbiter for a final precaution to make sure.

Especially for electronics in an impactor / penetrator as that would have to withstand high g force and perhaps high temperatures too, so it would need to use specially hardened electronics. And it needs to be hardened for the ionizing radiation for Europa as well so you are hardly talking about “off the shelf” electronics here.

A rather more far out idea - 3d printer on Europa plus raw materials for some of the components

Another idea, just for fun for now - but: land a sterile 3D printer + some raw material feedstock for it, also sterile. The surface would be high vacuum, ideal for electronics. First thing it does is to 3D print a shelter for itself or dig below the surface for protection from the cosmic radiation. Then it sets about printing out whatever you need, including a Europa submarine from the sterile components you supplied it with. If it is a nanoscale printer it can do circuit boards as well. So all you need to do is to send it some sterile chips to attach to those circuit boards, and other hard to print out components pre-sterilized. Most of the rest it does itself.

This is a bit far future perhaps.But perhaps some element of 3D printing could help for an idea of partial in situ construction of devices for helping to study Europa in a sterile way? Especially small chipsat type devices. Sterile electronics plus 3D printing of some extra components to help with mobility or sampling or some such.

If we can’t achieve 100% sterile landers for Europa

If we can’t do it, I think we simply should not send a lander or submarine to Europa until we can, and should not risk introducing Earth microbes to a habitable environment on Europa.

It is just risking too much to do that. Not just for us, not just for the mission that goes to Europa right now, but for our descendants and indeed all future civilizations on Earth also. It would be just tragic to find some interesting form of exobiology on Europa only to know that we have seeded Europa with microbes that will eventually make it extinct.

It could be very vulnerable to Earth life. The example I like best there is the idea of some primitive early life, for instance RNA based, or even an RNA ocean or autopoetic cells. If Europa was like that, then introduced Earth microbes in a globally connected ocean through exponential growth would surely do short work of converting it all to DNA based life.

Why not just send Earth life there?

Some enthusiasts suggest we just send life to Europa to seed it with Earth life. The problem with this idea is that then we won't be able to find out about the life that is already there, if there is any - or pre-biotic or non biotic chemistry - or whatever there is there right now. Especially since our life could make it extinct. About half of Earth's biological history in terms of gene complexity is unknown to us. We just have no idea how the early organic chemicals developed into lifeforms as complex as the simplest microbes. Lot's of sketched out suggestions but no answers and it is way beyond any attempt to simulate in a laboratory.

Well one likely thing to find in the Europa ocean, if life is common, is some early form of life. Maybe RNA based life. Maybe just an RNA ocean. Or maybe autopoetic cells. Or some primitive lifeform that reproduces, sort of, but not nearly as accurately as DNA life does. Or perhaps it's RNA based using ribozymes in the place of ribosomes, everything done in RNA. And that's just a few examples based on what might have happened in our own planet's past. Europa life may well not be related to Earth life at all. In the entire history of the solar system, at most a handful of rocks may have made it from Earth to Europa. So it could be something else as well.

As those examples show, it could be very vulnerable. An RNA ocean say, or RNA only lifeform could perhaps become extinct after just a few years of exponential growth after the first contamination by Earth life throughout the entire ocean, especially if it is all connected and its ocean has food sources for the life to use. And however quickly or slowly it happens, there is no way we could reverse something like that once it got started. It would be the worst possible anticlimax to all our searches for life in our solar system, to know that Europa was such a biologically fascinating place, until the first probes from Earth landed there, and is no longer like that.

Until we know what's there, I think we have to treat every potentially habitable planet or moon or other habitat in our solar system as if it was the only one of its type in the solar system. Because a lifeform that evolves in Europa's ocean may well not evolve in Enceladus, or Ceres or on Mars or whatever place you study next. It could be our only opportunity for light years in every direction, to study such a lifeform.

  • Perhaps they all have different unique lifeforms or types of pre-biotic life.
  • Perhaps they all have almost identical independently evolved life (very surprising I think).
  • Perhaps life from a previous star seeded them all or most of them.
  • Perhaps only one of them has life, or none of them do.
  • They are sure to have complex chemistry and we can learn from that also, maybe learn that life evolves only with great difficulty and find out what happens when it doesn't evolve too. We won't know until we find out.

As for experiments in Earth based life in space - we can do closed system habitats to try that out anywhere. For instance the Moon may have vast caves kilometers in diameter, so maybe we do it there. Or in free flying space habitats. There's enough material in the asteroid belt alone to create habitats with a total land area a thousand times that of Earth. There may be many opportunities to do that. We don't need to have as our first priority to turn everything into the closest possible approximation to Earth we can imagine, especially a very poor imitation of it, an ocean covered in kilometers of ice with the harsh environment of Jupiter's radiation on the surface, and too far from the sun for most photosynthetic life to be practical and not at all in its oceans (except for life that uses the heat radiation from hydrothermal vents for photosynthesis).

And meanwhile constructed habitats from asteroid materials can be designed with whatever environment you like, tropical gardens if you like, depending how much sunlight you reflect into it using space mirrors or solar collectors, or simulate conditions on Europa or Mars or other places in our solar system if that's your aim. Or you could simulate some the conditions on an interesting exoplanet. You can use spinning habitats with artificial gravity for whatever level of gravity you want, too.

That's looking forward a bit there - but only decades, centuries at most. You could build a Stanford Torus habitat within a decade or two with the funding and political will to do so even with present day technology. If we want to explore setting up habitats with Earth life in it outside of Earth, I think things like that would be the way to go - starting on a much smaller scale first probably. You could start with small exovivaria in LEO or on the Moon, and experiments with closed system recycling.

While there’s no way we can duplicate the billions of years of Europa’s history and the vast oceans larger than Earth’s oceans. If we mess it up, then the nearest “Europa” analogue may be light years away. And even then, chances are that if Europa and some Europa analogue both have life, even then most likely it has its own unique lifeforms, probably not even the same informational polymer in the place of whatever Europa has - not at all likely that it has the same lifeforms or proto life that evolved on Europa.

So why did they send a lander to Titan instead of Europa?

I think it might be partly that they were sending a spacecraft to the Saturn system anyway. In the case of the Jupiter system, then it’s much harder to visit Europa for more than a short time because of the ionizing radiation. Still you could do a penetrator with a fast flyby and that would work much like Huygens. It could communicate back to Earth during the flight to Europa and if it survived the landing, do some experiments and report back during its design life whatever it is.

But it would have many more planetary protection issues to work through than a Titan mission. I think myself it is best to wait for the orbiter mission first before we decide what to do next. We might well confirm the plumes on Europa and that would make it really easy to sample it’s ocean with a low flyby or orbiter and then we might not need a lander at all for the first missions there.

In situ instrument capabilities

During the Q / A, the team mention the idea of sending in situ life detection instruments to Europa in the future. We could use these on a flyby or a lander. So what instruments could we send? Actually there are many such already developed. Some of them have exquisite sensitivity, and could find life based on the minutest of traces, even able to detect a single molecule in the sample of biochemical interest.

Most of these instruments were developed for Mars. Whether they can be used as is for Europa, or need more modification, this shows the range of instruments we can send. I've no idea about the engineering challenge, to examine materials captured in an aerogel "in situ". One issue is to ensure that the readings are not confused by the material that makes up the aerogel so the composition of the aerogel is important. It also helps if you can do a slow flyby, so that there is less damage during impact into the aerogel. Anyway here are some of the instruments we can send, and some are exquisitely sensitive and would surely detect life if it is there.

I think if astrobiologists were asked, maybe in a competition to devise astrobiological instruments to send to Europa, they would rise to the challenge to devise instruments for a Europa flyby and you might get some surprises, neat ideas that you didn't expect. With the huge mass of the Europa missions on SLS, you could fly many of them - a lot of them are "labs on a chip" that weigh hardly anything.

Here are some ones that are already at quite a developed state, with an eye to eventually fly to Mars:

Rapid non destructive preliminary sampling

  • Raman spectrometry - analyses scattered light emitted by a laser on the sample. Non destructive sampling able to identify organics and signatures for life. It's sensitive, can measure the distribution of the organics and other compounds by pointing the laser at different points on the surface - and is non destructive so it can be applied first before any of the other tests.

Detection of trace levels of organics and of chirality

Direct search for DNA

These can detect life on Mars if it is DNA based so related to Earth life. As DNA sequencers, they can sequence the entire genome of any lifeform found.

  • Miniaturized DNA sequencer could work if we had a common ancestor right back to the very early solar system whenever DNA first evolved. This is in a reasonably advanced state. They say it could be ready to fly by 2018.

Electron microscope

Search for life directly by checking for metabolic reactions

These can detect life even if it doesn't use any recognized form of conventional life chemistry. But requires the life to be "cultivable" in vitro when it meets appropriate conditions for growth.

  • Microbial fuel cells, where you check for redox reactions directly by measuring the electrons and protons they liberate. This is sensitive to small numbers of microbes and has the advantage it could detect life even if not based on carbon or any form of conventional chemistry we know of.
  • Levin’s idea of chiral labeled release, where he has refined it so you feed the medium with a chiral solution with only one isomer of each amino acid. If the CO2 is given off when you feed it one isomer and not with the other, that would be a reasonably strong indication of life.This has the advantage that the life just needs to metabolize amino acids, and to produce a waste gas that contains carbon (such as methane).

There are many instruments like this we could send, and several of them are already space qualified but never flown.

Optical microscopy

I also wonder about an optical microscope. Why not send, not just a "geologist's hand lens" but a diffraction limited optical microscope? With resolution of 200 nm. It could tell us things about the behaviour and structure of micro-organisms or protocells we might not be able to find out by other methods. 

Ideally you want to see the structure of protocells if they exist, and other sub-optical limit structures, so I do wonder also about the microscopes that go beyond the diffraction limit, but I'd have thought they are probably too complex to send into space? Probably won't verify life or protolife unless it is actually still viable and active. But could give interesting data in combination with the other instruments.

What if we get ambiguous results like Viking?

Yes we might well get get ambiguous results. That's how science works. But if we are so scared of ambiguous results that we never fly anything unless we are sure it will give a clear cut result - surely that's going to slow down the pace of discovery? If you only search for things you know you can discover, with proven instruments you have already sent into space, you may be missing out on new discoveries that perhaps could be made easily with different instruments..

After the ambiguous Viking results, we should have done a follow up to resolve the ambiguity, e.g. using Levin's idea of a chiral labelled release to test uptake according to chirality of the organics. That's the scientific way to deal with it, not to give up, but to try to find out what happened. We have competing theories about what happened with Viking, but without further experiments, you can't resolve it just through theory.

Then also, negative results are mportant. If you send a DNA sequencer to test for DNA - well it is one hypothesis that Europan life could be related to Earth life through cells from before the origins of our solar system. If you find other indications that may indicate life, or strongly indicate it, but no DNA that's a significant null result. Based on that one can decide what to fly in the next mission for a follow up.

Europa is only two years travel time from Earth, and by the 2020s we may have more heavy lift capabilities that will make it easy to send follow up missions to resolve the questions that early missions raise. And as well as that - just sending the instruments at all gives exobiologist experience in sending their instruments in space, which then become space rated for future missions, so adding to exobiology experience. It also helps inspire a whole generation of astrobiologists, to see their instruments fly in space. At the moment only geological instruments have flown, apart from the very early Viking instrument. You have to start somewhere with the astrobiological in situ searches.

See also

Part of this article originated as my answer toIf there is a possibility of life on Europa, then why did NASA land a craft on Titan and not Europa? on Quora


Objective for humans to Mars

I think that our objective for humans to Mars should be humans to Mars orbit and possibly Phobos and Deimos, exploring the surface via telepresence. And as for our first experiments in biological closed systems, paraterraforming, commerce from space etc, I think all of those should be done on the Moon and in NEOs, leading later to exploration throughout the solar system. But the places of most interest for the search for life need to be protected indefinitely, until we know enough to make informed decisions about them. The top priorities there are Mars, Europa, Enceladus, and then there are others that need to be investigated before we know if they are vulnerable such as Ceres.

12th April 2011: International Space Station astronaut Cady Coleman takes pictures of the Earth from inside the cupola viewing window.- I've "photoshopped" in Hubble's photograph of Mars from 2003 to give an impression of the view of an astronaut exploring Mars from orbit. For more on this see my Telerobotics with humans in orbit compared to robots controlled from earth in Case for Moon First

See also this section of my Case for Moon First (and following) which may give pause for thought:

For more about the flow like features habitat, and many other possible habitats on Mars, see my

(notice I put the Richardson flow-like features on the cover - for me, this is the most exciting feature of all on Mars for exobiology)

Places on Mars to look for Microbes, Lichens, ... Salty Seeps, Melt Water Under Clear Polar Ice, Ice Fumaroles, Dune Bioreactors, ...: Where early Mars lifeforms could survive to the present day,

It’s also available to read online for free at Places on Mars to Look for Microbes, Lichens, ... and the section on the Richardson flow-like features is here: Flow like features

Safe ways to get humans to Mars orbit or its moons to avoid any risk of crashes on the surface

You couldn't do aerocapture in the Mars atmosphere as a way to get into orbit. It would be far too risky. Also Hohmann transfer with insertion burns are too risky also, as the insertion burn is done as close to Mars as possible to reduce the amount of fuel needed due to the Oberth effect. So you would need to be very sure that the insertion burn can't go on too long and end up on an impact trajectory with Mars.

I suggest ballistic capture is a far better method for human missions to Mars. The idea is that you launch the spacecraft to arrive ahead of Mars at just the right point for it to capture you as a temporary satellite. Once you leave Earth, you are already on a trajectory that ends up with your spaceship getting captured temporarily in a distant Mars orbit when it gets there, with no need for an insertion burn. Then once you are in that orbit, you use ion thrusters to spiral down to lower permanent orbits around Mars.

This is surely the safest of all the ways proposed to get into a Mars orbit, and the best way to prevent a crash of a human occupied spaceship on Mars.

Then you also have the flybys. Flybys are safe because although they involve precision targeting, you have months to set the target up. Also, the ones that are of most interest for Mars are free return, so even if your rocket fails, you are still on an orbit that will take you back to Earth again. You would use trajectory biasing of course, so that as you leave Earth you are biased away from Mars rather than towards it and use fine adjustment then to target the flyby orbit.

We have done many flybys, delicate ones, repeatedly for Saturn's moons with Cassini, and get them right every time, so it is obviously one thing we know how to do reliably. This has no time critical insertion burns. Just gentle thrusts nudging until you are in the right trajectory, which you set up long in advance of the actual flyby.

So, especially Robert Zubrin's double Athena flyby - a very interesting mission - is safe for humans to Mars. This has two flybys of Mars. The first diverts you into an orbit that closely parallels Mars for half of its year, so a full Earth year. The second flyby takes you back to Earth 700 days after the launch. It's free return - once you leave Earth you are already on a trajectory that will take you back to Earth 700 days later even if your rocket motors fail completely.

It's a great orbit for telerobotics as you spend several hours close enough to Mars for direct telepresence with each flyby, and days close enough for significant advantages relative to Earth, and over the entire one year period when you are almost paralleling Mars in its orbit, your crew are much closer to it for controlling robots on the surface than anyone on Earth.

Telerobotics as a fast way for humans to explore Mars from orbit

Telerobotics lets us explore Mars much more quickly with humans in the loop. And you'd use an exciting and spectacular orbit for early stages of telerobotic exploration of Mars, following the HERRO plans. It comes in close to the poles of Mars, swings around over the sunny side in the equatorial regions and then out again close to the other pole, until Mars dwindles again into a small distant planet - and does this twice every day.

Imagine the view! From space Mars looks quite home-like, and the telerobotics will let you experience the Martian surface more directly than you could with spacecraft, actually touch and see things on the surface without the spacesuit in your way and with enhanced vision, blue sky also if you like. It's like being in the ISS, but orbiting another planet.

12th April 2011: International Space Station astronaut Cady Coleman takes pictures of the Earth from inside the cupola viewing window.- I've "photoshopped" in Hubble's photograph of Mars from 2003 to give an impression of the view of an astronaut exploring Mars from orbit.

This is a video I did which simulates the orbit they would use - in orbiter. I use a futuristic spacecraft as that was the easiest way to do it. Apart from that, it is the same as the orbit suggested for HERRO.

It would be a spectacular orbit and a tremendously humanly interesting and exciting mission to explore Mars this way. The study for HERRO found that a single mission to explore Mars by telepresence from orbit would achieve more science return than three missions by the same number of crew to the surface - which of course would cost vastly more. Here is a powerpoint presentation from the HERRO team, with details of the comparison.

Then, you'd also have broadband streaming from Mars. As well as being very safe, also comfortable for the crew, you'd also have wide-field 3D binocular vision. It's amazing what a difference this makes, I recently tried out the HT Vive 3D recreation of Apollo 11. We'd have similar 3D virtual reality experience of the Mars surface.

Also, it would actually be a much clearer vision than you'd have from the surface in spacesuits, digitally enhanced to make it easier to distinguish colours (without white balancing the Mars surface is an almost uniform reddish grayish brown to human eyes)|.

Here is this hololens vision again, which though it's not telepresence, I think gives a good idea of what it might be like for those operating rovers on Mars in real time from orbit, some time in the future with this vision.

It's safer too. No need to suit up. No risk from solar storms - at worst you have to go to a storm shelter in your spaceship, not rush back to your habitat as fast as you can to get out of the storm in time. No risk of falling over and damaging your spacesuit. And when you need to take a break, have your lunch, or whatever, you can just take it up again where you left off, indeed leave the robot doing some task while you have your lunch or sleep.

Imagining a telepresence mission in the HERRO molniya type orbit

Imagine yourself in orbit around Mars - in a Molniya orbit - comes round to the sunny side of Mars twice a Martian day - you go really close to the surface - and spend some time there controlling rovers on the surface - driving them around - with reality headsets like the Occulus Rift -

- the Mars astronauts in orbit could explore the surface with headsets like this - and haptic feedback gloves so you can feel what you are doing, and omni directional treadmills like the virtuix omni

and automatically enhanced vision

with everything you see on Mars streamed back to Earth so everyone back here can join in and see what you see exactly as you see it whenever you explore the surface of Mars.

Then after a few hours of that you see that Mars is now getting further away, becomes smaller, and then 12 hours later you come in again for another close approach and real time exploring - you can continue to explore all the time - but when you are really close you can control things on the surface in real time as if you were there.

Small planes and entomopters etc

You could fly planes around on Mars, small planes, or entomopters - same design as a bumble bee. Lightweight, you could carry many of these along with the humans in a human mission to Mars orbit or the Mars moons to send on to the Mars surface.

Many other ideas like that - surely much more fun, to operate those from orbit around Mars, in a shirt sleeves environment than living a troglodyte existence on the surface under meters thick layers of soil, going out only rarely to keep down your lifetime radiation dosage - and knowing all the time that just by being there you have contaminated Mars and made it far harder for scientists to find out interesting things about biology and alternative forms of biology and the early history of evolution.

Also all this would be great for collaboration - probably need a big international expedition to send the humans out to orbit around Mars. But as well as that, anyone who can send a spacecraft to Mars (probably many countries by then) can send landers, for them to operate telerobotically. The more the better really. So it is something that all countries with interest in space could work on together, each contributing different things depending on their expertise.

More ideas for these early orbital or flyby missions

With of HERRO, and indeed for the other missions also, you could send supplies to Mars in advance in separate duplicate spaceships before the human mission gets there. Most of the cost of an innovative mission is in the design, so it often adds little to the costs, percentage wise, to make several duplicates of the spaceship.

So, you have a habitat there already, in orbit around Mars,and with all the systems functioning including life support. Preferably, have two such ships filled with extra supplies, before you send the first humans there.

They would be fully fueled lifeboat ships able to get the crew back to Earth, or for them to survive in if systems in the main ship fail. You can also use them as extra living space at Mars during the mission, and as long term assets in Mars orbit.

Since these lifeboat ships don't need crew or provisions for the journey out - they could be filled with extra supplies, fuel and spare parts instead. These supplies could then be transferred to the main ship and used as extra shielding for the stay at Mars. In the worst case you can cannibalize the other ships themselves, for repairs, or if the main ship fails, transfer the mission to another ship.

And - if we were looking forwards towards such an expedition - all rovers to the surface of Mars could be fitted with binocular vision and hands with haptic feedback by default. Anyone who sent a spacecraft to Mars would be sure to set it up so that it can be controlled easily by telepresence whenever there are astronauts in close orbit around Mars.

Suppose we had a lead time, say of a decade in the run up to the first human missions to Mars orbit (during which we have human missions to L2 etc). Then by the time humans get there, we'd have a decade worth of Mars rovers and landers, all equipped to be controlled via telepresence, ready for use when the first human missions get to Mars orbit.

Later orbital missions could mine Deimos for materials, using the likes of the Kuck mosquitoes - dedicated small spacecraft to shuttle materials back and forth from the moons to the settlements. If there is ice in Deimos; you could use this as rocket fuel to export this extra shielding to the habitat,

Artificial real time

But there is another thing we can do - and that's to do autonomous exploration from Earth, using "artificial real time" which lets you drive a rover around on Mars even with a huge time delay of minutes. At the moment the way we control our rovers on Mars is hugely time inefficient. We could as easily control rovers on Pluto, because they download the data for one day, and use that to direct the rover's operations for the next day.

There's no point in trying to speed that up though, because it is hard to get a data link from Mars to Earth. Once a day is about all we can manage easily, because our orbiters have their own work to do.

If we have a dedicated link though between Mars and Earth, satellites in orbit around Mars just to relay signals to Earth - our rovers could be hugely speeded up.

And - in a situation like that, we could also speed them up so much that using this idea of "artificial real time" from computer games, we could control them almost as easily as a rover on the Moon (say).

Standing Space found this interesting video about the idea:


Telerobotics with humans in orbit compared to robots controlled from earth

That's not to say that humans to orbit controlling robots on the surface would be better than robots controlled from Earth, bearing in mind the costs of the two types of mission. I don't know if anyone has done a comparison study there.

You might be able to compensate for the advantage of humans in orbit by having many more robots on the surface for the same cost, especially if broadband communication is possible, better robotic autonomy, and techniques from gaming such as artificial real time (building up a copy of the Mars surface explored by your robot in your computer on Earth and navigating that to help speed up movement from a to b on Mars).

But a human expedition might well capture the public imagination and so permit a much faster exploration of Mars from orbit. And would be an exciting and fun expedition to follow, and interesting for the crew too.

As a later mission you could then go on to explore Phobos and Deimos. They have many advantages for exploration. For instance Phobos has meteorites and micrometeorites throughout its surface layer of regolith, from the entire history of Mars, back to when Phobos first formed or was captured. This probably includes meteorites from the time when Mars had global oceans and then later on, lakes. Our Mars meteorites on Earth all left Mars no more than twenty million years ago (because the terrestrial planets clear their orbits so NEOs have to be replenished over a twenty million year time period).

Deimos also has a Mars facing crater which helps protect it from cosmic radiation, and solar storms - Mars obscures it from the sun in its local daytime, except for a few hours a day. Deimos may well have ice too, as it is related to a type of asteroid that often does have ice in its constitution.

There are many other advantages and points of interest of Mars' two moons.

For more on this, see my: 

Exploring Mars By Telepresence From Orbit Or Phobos And Deimos

So, how soon can we do such a mission? I suggested that while we explore the Moon robotically, we work on closed systems research, and also artificial gravity in LEO. That makes sense for a Moon base which you plan to keep occupied for years on end. But what about a first flyby of Mars? When could we try that?

Need for new comparison studies of the various ways of exploring mars

The HERRO comparison was just a small scale study, done several years ago. But I don't know of any other. It's surely high time that we had a much more thorough and detailed comparison study of the various possible ways of exploring Mars.

We may get practical experience of telerobotics in space with lunar missions in the near future. When that happens I think we'll find that machines are far more capable than they were in the days of lunakhod, operated from Earth most of the time, semi-autonomous, route finding on their own, able to do many things just by themselves with occasional help from Earth.

In a situation like that - operated remotely from Earth, or semi-autonomous, doing a lot of their own driving from place to place and then the crew in orbit around Mars step in to control robots that need particular help. I think that it would be much more than a 3 to 1 ratio compared with them working directly on the surface in spacesuits.

And everything they saw would be streamed back to Earth in HD meaning that after an astronaut has just walked past a place and maybe glanced at a rock via telerobotics, amateurs and experts back on Earth can explore that footage with the same direct telepresence, binocular vision etc. experience, and maybe alert them to something they missed.

I think a proper comparison study has to take all of this into account. I think a proper comparison study is probably best done by neutral parties or best perhaps, a workshop / panel that includes proponents of both sides in the debate as well as neutral parties. The cost of such a panel or workshop would be peanuts compared to the costs of the missions that we might commit to in the future for the exploration of Mars.

Compared with Mars surface missions

First of all, whatever the cost, I don't think that COSPAR should pass a humans to the Mars surface mission for planetary protection reasons.

Artist's impression of a human astronaut on the Mars surface holding Oskar Pernefeldt's proposed International Flag of the Earth - the linked rings symbolize how the different parts of Earth are linked together. (This is the latest of several proposed "Flags of the Earth"). 

Before a mission like that could be approved, a COSPAR workshop would need to show that it is consistent with planetary protection requirements, and would not risk introducing Earth life to Mars surface habitats.

Either that or there would need to be international agreement that Mars no longer needs to be protected from Earth microbes. To my mind, seems unlikely that either could happen before the 2020s or 2030s. As for the idea of a compromise based on humans contaminating only part of Mars, I find it hard to see how that could be approved by COSPAR either. How could the experts in the COSPAR panels sign their name to a statement that they know could lead to Earth life being irreversibly introduced to Mars? I don't really get it, how that could happen.

Meanwhile we could use telerobots to plant flags on Mars if that is the main aim of the mission or to touch Mars. Or if humans touching somewhere else other than Earth and the Moon are considered vital to this mission, we can plant flags on Phobos or Deimos and touch those moons instead.

In more detail there - the Outer Space Treaty is the only treaty we have to prevent siting weapons of mass destruction in orbit, or nations laying military claim to the Moon, etc - it's the main reason that we are able to do peaceful co-operative exploration of space. As well as the outcry from space scientists, the international upheavals resulting from something like this would be enormous. There is no way that the US or NASA could do this.

So, it's the same for planetary protection provisions based on the Outer Space Treaty. They are like quarantine laws; it doesn't matter how you get into space, you are still bound by them as a citizen of your country, which in turn is a signatory of the OST. The US has agreed to make sure that any US citizen or anyone using US hardware will keep to the provisions of the Outer Space Treaty. and the same applies to any other signatory of the OST which includes just about all nations either space faring or with space faring ambitions. The United Arabic Emirates hasn't yet ratified the OST but they will still keep to the provisions.

Cost savings compared with surface missions

It's interesting to notice that these orbital missions would cost less than a surface mission. Especially HERRO and the double Athena which Robert Zubrin proposed as a lower cost precursor mission. This is a powerpoint presentation from the HERRO team, with details of the comparison.

The reason the orbital missions can do so much more in the same time period compared with a surface mission is that

  • You can control rovers anywhere on the surface of Mars, so can explore multiple sites at once.
  • There is no need to suit up and travel to the area of interest, you can do it all with shirt sleeves environment within the spacecraft.
  • When you take account of the reduced mobility of a human in a spacesuit, with clumsy pressurized gloves, then there's no great advantage of humans over telerobotically controlled rovers on the surface as far as mobility is concerned. Spacesuit technology of course will advance, but so also does telerobotic technology.

Then as well as that, there is no need at all to develop technology to land a human mission on the surface of Mars. That's not just a matter of delta v. You can land on Phobos or Deimos with a gentle use of delta v over a long period of time, and right up to the last minute, as for the Moon, if anything is wrong with your trajectory, you just abort and move away from the moon a bit, figure out what went wrong and try again, with hardly any waste of delta v due to the low gravity of these moons.

With a landing on Mars surface, everything has to go exactly right during the "eight minutes of terror" of the Curiosity landing. There's also almost no chance of humans intervening to save the mission if something goes wrong, as everything happens so quickly.

So - that's a whole new technology needed for a Mars surface landing that isn't needed at all for a Mars moon landing. And major human safety issues with a Mars surface landing that again are not issues at all for a Mars moon landing.

Then with the new ballistic trajectory idea, it's possible that you could get to a low Mars orbit for similar delta v to a surface mission anyway.

Even if it weren't for the planetary protection issues then telerobotic missions would seem to be the way to go for more science return and indeed a more immersive way to explore Mars than a surface mission.

Summary of advantages of telerobotic exploration

  • Best solution for planetary protection. It is hard to see how you could send humans to the surface of Mars without a risk of a hard landing which would contaminate a random area of Mars with all the hundreds of trillions of microbes in tens of thousands of species that accompany humans. If you introduce Earth life to Mars there is a major risk that you will detect life on Mars only to find that you brought it there yourself.
  • Costs far less for more science return
  • Far safer for the crew to get there. The landing on Mars is the most risky landing almost anywhere in the inner solar system, because the atmosphere is too thin for a parachute landing - and yet - there is just enough atmosphere so that once you start the landing sequence you are committed, unlike e.g. the Moon where right up to the touch down itself, the crew could blast off into space again. You can't do that on Mars because to go up into space again you need enough fuel to overcome the resistance of the atmosphere.
  • Exploring is also far safer. Crew at all times remain in shirt sleeves environment in the orbiting spacecraft. All they can endanger is the "avatar" rover they control on the surface. And that, if damaged, can be repaired potentially. While if e.g. you damage your air supply to a spacesuit you die. The rover can spend days, weeks, even months just at one spot on Mars using only electricity from sunlight while a human explorer has to return to base for provisions, oxygen etc. It doesn't have to put on a spacesuit every day, which takes up an hour or two of every day.
  • Crew can explore several parts of Mars simultaneously, and "teleport" instantly from one experiment to another - leave one rover doing routine analysis while they drive another, or direct sampling for another - so the crew do all the interesting stuff and the rovers do all the dull stuff by themselves.
  • Mars from orbit looks quite Earth like, an interesting planet and the elongated HERRO Molniya orbit is especially stunning with close flybys of the spectacular landscape and the polar caps every twelve hours, with the landscape skimming past below your spaceship followed by a long fly out so far that Mars becomes quite small. Every day you have that experience, twice, and each time coming in over a slightly different part of Mars. On the surface you'd be stuck in a single spot from then on and probably not see that much, and in the dust storms, nothing at all.
  • When you drive the rovers on the surface with telepresence and haptic feedback, and virtual reality goggles to see the Mars landscape in 3D - you'd experience the surface vividly, far more so than if you were really there. Our eyes are not adapted to the Mars light and everything would seem dim and reddish brown, with colours hard to discern and a dull butterscotch sky. Exploring via avatars we can colour adjust automatically to resemble Earth lighting conditions, indeed with a blue sky if you like.
  • Whatever you see and feel is already digital streaming, so can easily be recorded and streamed back to Earth and so we can experience it here, just as you did. And examine the images to see if we spot anything you missed. And if anything goes wrong on the surface, again, you have everything recorded and streamed, so we can figure out what happened, no possibility of an unknown accident where someone falls and dies and nobody is sure why it happened.

Collective sense organs for humankind on Mars

This idea that perhaps we shouldn't send humans to the surface of Mars because we'd contaminate it with Earth life is not much mentioned in the news. Out of dozens of news stories about ideas for human missions to Mars, perhaps only one or two will ever even mention it as an issue.

But it's frequently mentioned in the academic literature on spaceflight, with many publications debating the issue, and several planetary protection workshops on human missions to Mars. It's just that their deliberations rarely get into the news.

Here is a quote from "When Biospheres Collide":

"One of the most reliable ways to reduce the risk of forward contamination during visits to extraterrestrial bodies is to make those visits only with robotic spacecraft. Sending a person to Mars would be, for some observers, more exciting. But in the view of much of the space science community, robotic missions are the way to accomplish the maximum amount of scientific inquiry since valuable fuel and shipboard power do not have to be expended in transporting and operating the equipment to keep a human crew alive and healthy. And very important to planetary protection goals, robotic craft can be thoroughly sterilized, while humans cannot. Such a difference can be critical in protecting sensitive targets, such as the special regions of Mars, from forward contamination.

Perhaps a change in the public's perspective as to just what today's robotic missions really are would be helpful in deciding what types of missions are important to implement. In the opinion of Terence Johnson, who has played a major role in many of NASA's robotic missions, including serving as the project scientist for the Galileo mission and the planned Europa Orbiter mission, the term "robotic exploration" misses the point. NASA is actually conducting human exploration on these projects.  The mission crews that sit in the control panel at JPL, "as well as everyone else who can log on to the Internet" can observe in near real-time what is going on. The spacecraft instruments, in other words, are becoming more like collective sense organs for humankind. Thus, according to Johnson, when NASA conducts it's so-called robotic missions, people all around the world are really "all standing on the bridge of Starship Enterprise". The question must thus be asked, when, if ever, is it necessary for the good of humankind to send people rather than increasingly sophisticated robots to explore other worlds"

See When Biospheres Collide


See also my books:

"MOON FIRST Why Humans on Mars Right Now Are Bad for Science", available on kindle, and also to read for free online.

Case For Moon First: Gateway to Entire Solar System - Open Ended Exploration, Planetary Protection at its Heart - kindle edition or Read it online on my website (free).

Facebook group

I've made a new facebook group which you can join to discuss this and other visions for human exploration with planetary protection and biological reversibility as core principles. Case for Moon for Humans - Open Ended with Planetary Protection at its Core

See also

Robert Walker's posts - on Quora

And on Science20

Robert Walker's posts on Science20

Kindle bookshelf - for my author's page

And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon

Other things to cover


  • Exploration from a human occupied Mars base - impossibility of keeping the rovers as clean as they would be sent from Earth.
  • How contamination from Earth originated microbes would confuse searches for amino acids and organics
  • Present day life with different form of photosynthesis and comparison with synthetic life made in labs on Earth
  • Unlikely life on Mars has reached the exact same stage of evolution as us and could be either more evolved or less (even if microbial and lichens it could be more evolved or less evolved microbes)
  • How it is easy to argue that case both ways based on the different history of Mars
  • That the most vulnerable type of life we could find on present day Mars - early life - could go extinct maybe quite soon after contamination with Earth life
  • That we can touch Mars more directly through telepresence with enhanced vision, than on the surface in a clumsy spacesuit.