If Humans Touch Mars

Will It Be Another Tale Of Human Missteps Like Lascaux?


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

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

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In science fiction, artist's impressions, movies and the popular imagination, there is no question about it, that humans would touch Mars. Bold and brave astronauts explore the planet from Mars bases in pressurized rovers and wearing spacesuits. They look for fossils, 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 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. Their spacesuits would continually leak Earth microbes from the joints as they walk around on the surface. The dust is so light and easily moved in the wind that Mars dust storms can carry a dust particle as far as the opposite side of Mars in a single storm. 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. That's especially so after a Challenger type crash of a human crewed spacecraft on Mars, the planet could potentially be irreversibly contaminated with Earth life, so changing it for all time for those who want to explore Mars including all future generations and civilizations. 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, and they are not based on any actual experience of exploring another world?

At least nowadays scientific news stories about Mars sometimes mention this issue. 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, when they talk about human exploration of Mars, they briefly covered the need to protect Mars from Earth life, and 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 and we will have irreversibly introduced Earth life there already. So then we can just 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 it is so often just ignored completely as soon as the discussion turns to humans on Mars. Another video raising the issue 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 issues (starting nine minutes in),, but there is so much more to be said.

We have a long way to go when it comes to raising awareness in this topic area. As you read this book,you may be surprised by how difficult some astrobiologists think it will be to find past or present day life on Mars, how much value they place on in situ searches by sterilized robotic explorers with sensitive detectors such as SOLID3, and the many ramifications that could follow if humans touch Mars. The same issues apply for other potentially habitable places in our solar system, particularly Jupiter's Europa and Saturn's Enceladus with their subsurface oceans connected to the surface, while human explorers in other locations such as the Moon would have almost none of these issues.

I've written many articles and booklets and a couple of kindle books about the value of space resources, and the many ways that humans can contribute to exploring the solar system. I also argue strongly for the Moon as the obvious place to get started with human exploration, not just as a stepping stone to Mars, but as a place of great interest in its own right.

"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).

With our experiences of the role of humans in space exploration of the Moon, and practicalities of how to do it, we could send humans not just to Mars but to the Venus clouds, Mercury, Callisto, asteroids and further afield. We can explore Mars from orbit via telepresence as an immersive experience. This is similar to exploring a computer game generated world using 3D virtual reality, but this time the world explored is real. This could be a more direct way of experiencing it than with spacesuits on the surface. This may turn out to be the best way to do much of the lunar exploration too. We could even search for meteorites from Mars on Phobos, Deimos and our own Moon, along with meteorites from early Venus and from the distant past of Earth itself. And the search for life on Mars we'll see can be done more effectively with in situ rovers. We can actually probably do more exploration more quickly from orbit than on the surface, while protecting Mars from Earth life at the same time.

This is an exciting and adventurous alternative vision for humans in space which has none of the irreversible and possibly devastating consequences for science of touching Mars. I thought it's best to say that from the outset as I've found in the past that my readers sometimes read my articles as if they were 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. 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. Microbes adapted to extreme environments often manage just fine in ordinary environments as well, on and in our bodies, and on the surfaces of our spaceships. The organics that make up our bodies, our food, human wastes etc could also be a problem in the event of a crash on Mars. If we explore Mars via telepresence, then we can be there in person without these consequences of touching Mars. And with other places like the Moon, then we don't have the same issues.

Human settlement also 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. 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. But I argue also that it can have hugely positive consequences if done well. I cover this in my Case for Moon First under:

But there are many issues also for human exploration without settlement. 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.

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

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:

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.

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

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.

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.

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:

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.

With wind speeds of 10 to 30 meters per second average for the faster winds during a dust storm, they could travel 240 to 720 miles in twelve hours. 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. Not 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. 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 

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. 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:

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 hemisphere. 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:

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.

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.

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.

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:

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).

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.

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

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, ...:

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

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.

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.

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.

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.

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.

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


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 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.


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.


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.


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,


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:



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?


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.


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.


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

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.



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).


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


Robert Walker's posts - on Quora

And on Science20

Robert Walker's posts on Science20


And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon