If Humans Touch Mars

Safe return of unsterilized sample

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

Easy part, sample return to surface in container

The easy part is to return a sample to the Earth surface. That's pretty much worked out. The idea is that you have to break the "chain of contact" with Mars. Make sure nothing that has contacted the Mars surface or contacted anything else that contacted the Mars surface is exposed to Earth environment. The easiest way to do that is to use nesting capsules. The Mars sample is placed inside a larger capsule in Mars orbit. On return to the Earth system, you could indeed put it inside an even larger capsule enclosing both. Make sure that there is no way those capsules can be broken even in event of a crash landing on Earth.

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

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

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

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

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

The smallest size for early cells if they don't contain all the machinery of modern life, is generally estimated as about 40 nm. Successive studies by the National Research Council (NRC) in the USA (two studies) then the European Science Foundation (ESF) (one study) gradually lead to more and more stringent requirements. First came the reduction to 200 nm by the NRC after discovery of the ultramicrobacteria Then, that was reduced to 10 nm by the ESF. as a result of discovery of how readily archaea can share their DNA through the tiny Gene Transfer Agents (GTA's) Archaea can transfer genes between phyla that are as different from each other as fungi are different from aphids. It is an ancient mechanism and so may also be able to transfer genes from life that had last common ancestor with us in the early solar system. As we've seen already, In one experiment 47% of the microbes (in many phyla) in a sample of sea water left overnight with a GTA conferring antibiotic resistance had taken it up by the next day

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

Another thing that makes the design more complex is the need not just to contain the sample (which is usually done by a positive air pressure from outside) but also to protect it from outside organics (which needs a positive air pressure from inside). You end up with some kind of a double walled facility and they cite this as one of the main reasons why you have to have a new design of building, never tested before. This is one of the designs they came up with in 2008, with telerobotics.

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

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

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

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

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

Legal complexities

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

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

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

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

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

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

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

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

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

For more on all this see my:

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

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

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

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

• Gene transfer agents. These are much smaller than viruses, and they can transfer small fragments of DNA from one species to another to give them new capabilities. It's an ancient mechanism, and works between distantly related species. GTA's can transfer capabilities between species as unrelated as fungi and aphids (example of a GTA that gave an aphid the capability to create carotene, from a fungus). Also it works very quickly between microbes in sea water, if the GTA's ever got into the sea. In one experiment a GTA conveyed antibiotic resistance on 47% of the microbes in sea water, all types, just the microbes you have in sea water naturally, after they left them exposed to the GTA's overnight. This is relevant if Mars life is distantly related to Earth life. Even if the life got transferred from Earth to Mars or Mars to Earth billions of years ago, it could still exchange capabilities with Earth microbes readily using GTA's 
  
• Life not based on DNA which has chemical signatures that Earth based life is not designed to respond to. Our defenses would only respond to the trauma, not to the cause of it. This is a point made by Joshua Lederberg, Nobel prize winning microbial geneticist, in Parasites Face a Perpetual Dilemma and also in Exobiology: Approaches to
  Life beyond the Earth and a nice quote here: 
  
  "If Martian microorganisms ever make it here, will they be totally mystified and defeated by terrestrial metabolism, perhaps even before they challenge immune defenses? Or will they have a field day in light of our own total naivete in dealing with their “aggressins”? in his "Paradoxes of the Host-Parasite Relationship" (he also gives an interesting analogy there with symbiosis with mitochondria)
  
  In the worst case, of total naivete on the part of Earth microbes, lifeforms like this could live on our bodies, in our guts, and produce chemicals that are poisonous to us or take the place of microbes that we need to survive. Or just eat us. And our defenses might not respond. 
  
• Life from Mars could harm us in many other ways, not just directly as diseases of humans. If the life from Mars has a major effect on microbes that we depend on (like the algae in the sea) or on the plants we depend on for food, wood and so on, or on the animals, it could be just as disastrous for the environments on the Earth. As an example, cyanobacteria produce toxins that kill cows. There's no evolutionary advantage in this as far as we know, the cyanobacteria can't eat the cows and it's unlikely to be a measure to deter predation by cows. It's just a case of toxins that are effective over a large evolutionary distance. See Alien Infection (Astrobiology magazine, 2008). 
  
  For another example, cyanobacteria produce BMAA which is implicated in Alzheimer's. This is a chemical that resembles L-serine and can be misincorporated in its place and cause folding disorders in proteins, amongst other effects. Again there is no advantage to the cyanobacteria to cause Alzheimer's. in humans. And another nice example, cocoa plants produce theobromine which kills dogs if they eat too much chocolate. The cocoa plant doesn't need to defend itself against dogs. 
  
  In a similar way, microbes from Mars could easily produce toxins that have adverse effects on Earth life. 
  
• Life that out competes Earth life. One example here, what if Mars has some fourth form of photosynthesis different from the three main types on Earth.
  
  Our three types are:
  Green sulfur bacteria, which use light to convert sulfides to sulfur, which is then often oxidized to sulfur dioxide
  Normal photosynthesis which splits water to make oxygen, also taking up carbon dioxide in the process. (basic equation 6CO₂ + 12 H₂O → C₆H₁₂O₆ + 6O₂  + 6 H₂O where the oxygen atoms in bold are the same ones on both sides of the equation - see Plants don't convert CO₂ into O₂, and Notes on lamission.edu)
  The photosynthesis of the haloarchaea which works similarly to the receptors at the back of our eyes, based on a "proton pump" which moves hydrogen ions across a membrane out of the cell using bacteriorhodopsin similar to the rhodopsin in our eyes, with no byproducts such as sulfur or oxygen, just creates energy directly from the proton gradient.
  
  What if Mars life uses a fourth form of photosynthesis is more efficient at making use of sunlight than the methods used by the green algae in our oceans? The space of possibilities is so vast, there is no way that DNA based life on Earth has explored even all the possibilities for DNA. For instance, over many millions of years, higher lifeforms in Australia never developed the placenta or anything resembling a modern mammal, and so it was vulnerable to introduction of rabbits, which were not at all adapted to Australian conditions, but still easily out competed the native Australian marsupials. Similar things could happen at the microbial level for transfer between planets instead of continents. Mars microbes could have capabilities never explored in the entire history of evolution on Earth. 
  
  For another example, if not based on DNA, it could be able to do more with less. The microbes might be smaller, the encoding more efficient, less need for error correction, enzymes much smaller to do the same thing, it could be all round more efficient, and so able to manage on less by way of resources, with a more efficient metabolism. It might out compete Earth life everywhere where it can survive on Earth, by making do with less. 
  
• Life returned from Mars might have a different side to it, like harmless grasshoppers which some trigger can turn into locusts, some condition on Earth triggers a different behaviour or capability that never turned up when encountered on Mars or in transit. 
  
• Life returned from Mars could be harmless at first, until it adapts to Earth conditions, but then evolve to be a major problem later. For instance it might need to adapt to warmth, or to water that is less salty than on Mars, or to lack of perchlorates (if it tends to depend on perchlorates for food) or the denser atmosphere.
  
• It could be a slowly developing problem even without adaptation. E.g. back to that example of photosynthetic life that is just slightly better than Earth life, then it might take decades before sufficient numbers build up to replace the green algae and other photobionts in the oceans. Nevertheless, with exponential growth, there might be nothing we can do to stop its inexorable advance. 
  
• Mars life could also be totally harmless, as Carl Sagan said in Cosmos, "There may be no micromartians. If they exist, perhaps we can eat a kilogram of them with no ill effects. But we are not sure, and the stakes are high. If we wish to return unsterilized Martian samples to Earth, we must have a containment procedure that is stupefyingly reliable...here are nations that develop and stockpile bacteriological weapons. They seem to have an occasional accident, but they have not yet, so far as I know, produced global pandemics. Perhaps Martian samples can be safely returned to Earth. But I would want to be very sure before considering a returned-sample mission.”

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

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

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

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

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

• If any of the astronauts become seriously ill, they will be rushed to hospital and not permitted to die in the quarantine facilities. If you try quarantine in orbit, they will be returned to Earth as soon as they encounter any really serious health issue. This is clear from Apollo. The crane they had designed to pick the command module out of the sea had a problem. Rather than fix the problem and leave the astronauts bobbing in the ocean, getting seasick while the world watched, they sent a helicopter with divers, who took the astronauts out of the module, into an open boat, and put them into their suits. By then the dust from the module would be in the sea already and planetary protection was already compromised even assessed by the standards of their time. From this example to show how mission planners were ready to waive precautions just to prevent the astronauts from getting seasick for a few hours while they fixed the problem, it's clear that they would definitely not let their heroic astronauts die in the quarantine facilities if they became seriously ill. So the Apollo astronauts quarantine was a largely symbolic gesture which would have done nothing to protect Earth from any real hazard in the unlikely case that the Moon did have microbes hazardous to Earth. 
  
  It's not clear you can ethically keep them inside anyway if they get seriously ill in quarantine facilities designed to protect Earth from unknown dangers. At the very least it's a very tricky ethical and legal area. Even if they consent beforehand to be left to die there to protect Earth, it's not clear you can hold them to that in the event that it happens, especially if you have no idea whether there is some extra terrestrial cause - when it might well be some Earth based illness that needs to be diagnosed in the advanced facilities of a modern hospital to save their lives. 
  
• It only protects from diseases that affect humans or other lifeforms in the facility. You can't take all the higher animals we depend on, the trees, grasses, sea water, etc. etc. into the facility for testing
  
• You have to guess at the latency period. Some diseases of humans such as leprosy can remain latent for decades before anything happens. There was no scientific reason for choosing any particular quarantine period for the Apollo astronauts. It was just a guess and I haven't seen any reasoning to explain their choice. Quarantine does work fine when you know the maximum latency period, and if it is a reasonably short period. But it doesn't work if that period is very long or you don't know what it is. 
  
• It gives no protection from problems that manifest later. E.g. quarantine won't help at all if the microbes that humans carry with them need some time to evolve to adapt - either to terrestrial conditions or indeed even, to adapt to humans.

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

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

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

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

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

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

So, if we want to find traces of life on Mars, it seems pretty clear, that we need to find it in situ on Mars first, just for reasons of expense. The NASA plans would return a few hundred grams of crushed samples at a cost of billions of dollars, and this is too much to spend to return a sample that has only a small chance of containing any material of interest to exobiologists. It's true that once returned, we can analyse them over and again with more and more instruments - but that's only useful to exobiologists if we return the right samples in the first place. While we can send increasingly sophisticated instruments to Mars to study it in situ and explore a far wider range of possibilities there.

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

Suggestion for protection of earth during sample return - ionizing radiation

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

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

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

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

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

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

Current requirements for sample return and legal situation

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

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

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

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

Using ionizing radiation to sterilize the sample returned to Earth

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

So, my suggestion is, for the first sample returns from Mars, why not use ionizing radiation? Subject it to enough ionizing radiation to thoroughly sterilize even the most radioresistant microbes known such as radiodurans and chroococcidiopsis 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.

The Moon can also help bring us with the biological search for early life, rather surprisingly, through remains of life that landed there in meteorites. It has extraordinarily cold conditions at the lunar poles, in craters that have never seen sunlight for billions of years. They are colder even than Mars, so we could find organics there as well, preserved, hardly changed, since the early solar system. There may be organics back to soon after the formation of the Moon itself. Not just a few meteorites. There may be as much as 200 kilograms of material from early Earth per square kilometer of the lunar surface. We might find fossils also, fossil diatoms are still recognizable after a simulated impact on the Moon, indeed the smallest ones are intact, complete fossils. There must be a lot of material from the Chicxulub impact on the Moon - so perhaps there are fragments of ammonites and other sea creatures from the Cretaceous period, with organics still preserved, on the Moon. Perhaps the Moon will be one of the best places for fossil hunters in our solar system, outside of Earth.

Artist's impression of Cretaceous period ammonites, courtesy of Encarta. The Chicxulub impact made these creatures extinct. It hit shallow tropical seas and the ejecta could have sent fragments of cretaceous sea creatures such as ammonites all the way to the Moon. Fragments in the cold polar regions may even have the organics preserved.

The Moon must have meteorites from Mars too, for us to pick up. See section 3.1.1 of Back to the Moon: The Scientific Rationale for Resuming Lunar Surface Exploration. Even today, Earth gets around 500 meteorites from Mars as large as half a kilogram every year. though most fall in uninhabited areas, or the sea. So the Moon also must have meteorites from Mars right through to the present. They may be easier to find there, without the erosion processes that quickly merge them into the landscape in most places on Earth. The Moon may perhaps have meteorites from early Venus too, from before its atmosphere became as thick as it is now. Early Venus might have had oceans and might have been as habitable as early Earth and Mars.

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

Myth of automatic terraforming

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

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

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

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

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

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

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

Going to Mars Could Mess Up the Hunt for Alien Life

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Pristine Mars

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

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

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

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

Searching for a non confrontational way ahead

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

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

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

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

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

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

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

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

• Warm Seasonal flows (Recurrent Slope Lineae)
• Sun warmed dust grains embedded in ice
• Flow like features
• Life able to take up water from the 100% night time humidity of the Mars atmosphere
• Deliquescing salts taking up moisture from the Mars atmosphere
• Advancing sand dunes bioreactor
• Droplets of liquid water on salt / ice interfaces
• Shallow interfacial layers a few molecules thick

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

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

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

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

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

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

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

Value of a non confrontational approach

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

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

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

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

Moving your house to avoid a pond for great crested newts

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

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

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

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

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

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

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

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

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

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

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

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

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

Ponds and flightless parrots again - back to the Moon

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Clash and confrontation?

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

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

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

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

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

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

What about humans on Mars later on?

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

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

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

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

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

When will we know enough about Mars?

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

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

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

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

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

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

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

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

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

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

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

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

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

Only one Mars - no warp drive yet

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

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

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

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

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

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

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

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

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

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

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

Precautionary principle and super positive outcomes

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Searching for life on Europa and Enceladus

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

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

Hubble's confirmation of probable geyser activity on Europa

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

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

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

Hubble Sees Evidence of Water Vapor at Jupiter Moon

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

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

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

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

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

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

This seems a more likely scenario

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

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

How can we find out more?

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

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

Keeping safe - sample geysers

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

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

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

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

So then what about landing on Europa?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Ice knives on Europa

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

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

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

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

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

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

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

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

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

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

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

Possibility of liquid water close to the surface or breaking through

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

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

Can we sterilize a spacecraft 100%

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

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

Fast follow up landers

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

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

Mission to Enceladus geysers - and perhaps identical mission to Europa

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

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

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

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

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

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

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

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

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

In effect, you are creating an artificial geyser here. This would be followed by a low flying orbiter to capture the sample for analysis.

That would have minimal planetary protection issues if the dumb penetrators can be 100% sterile - e.g. just lumps of metal heated beforehand to temperatures where no Earth microbes could survive or otherwise 100% sterilized before impact. This is an idea Bernd Dachwald (head of the German IceMole project) once suggested to me in conversation, which I think is an interesting one.

However if Europa is indeed producing geysers naturally, we don't need to do this, we can just observe the plumes "as is".

Chipsats for Europa - could they be 100% sterilized?

Another interesting idea, here is an old mission idea to send “chipsats” to Europa’s surface, each one rather “dumb” but lots of them, each one consists of just a few sensors on a flat chip. Some would fail but enough would get through, and they would be able to survive impacts that a larger more complex lander couldn’t.

That sounds like a kind of a lander that is so minimal, perhaps it could be 100% sterilized by supercritical CO2 snow or something similar? That’s a technique that can remove all the organics from the surface of an electronics chip without damaging the chip. It’s been shown to work with USB drives. So though it might be tricky to scale up to a complete spacecraft, I wonder if it is good enough to 100% sterilize chipsats? It would have to be 100% reliable.

"ATTEMPT NO LANDING THERE" --New NASA Mission to Europa will Ignore Arthur C Clarke's Warning (2014 Most Popular)

Can we achieve 100% sterile electronics for a Europa or Mars lander?

There’s no in principle reason to prevent 100% sterile electronics. You just have to find some process that electronics can withstand and life can’t. If you heat metal to hundreds of degrees C for instance, no life will survive and the result will be 100% sterile. The problem is that this will destroy the spacecraft electronics too. So can we find a way to sterilize it of Earth microbes without destroying the delicate equipment? That’s the big question here.

Also all this might be far easier to do with a chipsat than with a large conventional spacecraft.

First one method being explored by the European Space Agency is Deep cleaning with carbon dioxide. and Science Daily article about it.

• CO2 a liquid at 100 atmospheres and 50 C.
• And then on release of pressure turns to snow and takes the dirt, organics, everything away leaving the surface dry.
• Mixed with Hydrogen peroxide and other chemical to increase effectiveness.
• Can be used even with sensitive electronics. Was used to clean USB drives in testing and they functioned afterwards.
• Surface is left with no trace of organics, not just with dead micro-organisms. Major plus!

Could you remove all traces of organics from the exterior in this way? And - can you also keep exterior and interior separate so there is no chance of leaking contamination from inside the mole?

High temperature sterilization

Then also, if you can make the whole thing able to withstand high temperatures, you can just heat it up to a high enough temperature to sterilize all life.

The main issue with sterilizing modern spacecraft is that many instruments are quite delicate, also they can go out of alignment,so even the sterilization temperatures used for Viking of 111 °C for 40 hours is too much for them.

But there are electronic circuits now designed to operate at up to 200°C . High-Temperature Electronics

And there are other developments that should permit temperatures of 200°C upwards :).High-Temperature Electronics Operate at 300 degrees C | EE Times and Designing for extreme temperatures

There’s an economic incentive for developing these electronics, as they are useful in oil wells and motor cars.

I’ve never seen this suggested for a way to keep Europa landers sterile, but it sounds as if it should work!

Back to the drawing board probably for a lot of the designs to make the whole thing uses chips and solders etc that work up to high enough temperatures for 100% sterilization. But it seems like it may be possible! Thanks to Adeel Khan for the suggestion

Is this right? Is it possible to achieve 100% sterilization by heating electronics that’s capable of resisting temperatures of up to 300 C. I wonder if anyone working in the field of spacecraft sterilization has investigated this, either experimentally or in theory. Or is there some other way to achieve 100% sterile electronics such as the CO2 snow approach?

I think we need to look into that myself before we consider sending any probes to habitats that may include liquid water habitable to Earth life. Except of course for the plume flybys. They are safe so long as the ice particles they collect can’t dislodge microbe spores and return them to the liquid water in the subsurface oceans. That sounds likely to be for all practical purposes, zero risk though you’d need to examine it carefully of course.

Multiple methods at once

Perhaps for the best results both can be used one after the other. High temperature to make sure there is nothing viable. Then CO2 snow to remove the organics as far as possible. Heat it up again before it is released from the orbiter for a final precaution to make sure.

Especially for electronics in an impactor / penetrator as that would have to withstand high g force and perhaps high temperatures too, so it would need to use specially hardened electronics. And it needs to be hardened for the ionizing radiation for Europa as well so you are hardly talking about “off the shelf” electronics here.

A rather more far out idea - 3d printer on Europa plus raw materials for some of the components

Another idea, just for fun for now - but: land a sterile 3D printer + some raw material feedstock for it, also sterile. The surface would be high vacuum, ideal for electronics. First thing it does is to 3D print a shelter for itself or dig below the surface for protection from the cosmic radiation. Then it sets about printing out whatever you need, including a Europa submarine from the sterile components you supplied it with. If it is a nanoscale printer it can do circuit boards as well. So all you need to do is to send it some sterile chips to attach to those circuit boards, and other hard to print out components pre-sterilized. Most of the rest it does itself.

This is a bit far future perhaps.But perhaps some element of 3D printing could help for an idea of partial in situ construction of devices for helping to study Europa in a sterile way? Especially small chipsat type devices. Sterile electronics plus 3D printing of some extra components to help with mobility or sampling or some such.

If we can’t achieve 100% sterile landers for Europa

If we can’t do it, I think we simply should not send a lander or submarine to Europa until we can, and should not risk introducing Earth microbes to a habitable environment on Europa.

It is just risking too much to do that. Not just for us, not just for the mission that goes to Europa right now, but for our descendants and indeed all future civilizations on Earth also. It would be just tragic to find some interesting form of exobiology on Europa only to know that we have seeded Europa with microbes that will eventually make it extinct.

It could be very vulnerable to Earth life. The example I like best there is the idea of some primitive early life, for instance RNA based, or even an RNA ocean or autopoetic cells. If Europa was like that, then introduced Earth microbes in a globally connected ocean through exponential growth would surely do short work of converting it all to DNA based life.

Why not just send Earth life there?

Some enthusiasts suggest we just send life to Europa to seed it with Earth life. The problem with this idea is that then we won't be able to find out about the life that is already there, if there is any - or pre-biotic or non biotic chemistry - or whatever there is there right now. Especially since our life could make it extinct. About half of Earth's biological history in terms of gene complexity is unknown to us. We just have no idea how the early organic chemicals developed into lifeforms as complex as the simplest microbes. Lot's of sketched out suggestions but no answers and it is way beyond any attempt to simulate in a laboratory.

Well one likely thing to find in the Europa ocean, if life is common, is some early form of life. Maybe RNA based life. Maybe just an RNA ocean. Or maybe autopoetic cells. Or some primitive lifeform that reproduces, sort of, but not nearly as accurately as DNA life does. Or perhaps it's RNA based using ribozymes in the place of ribosomes, everything done in RNA. And that's just a few examples based on what might have happened in our own planet's past. Europa life may well not be related to Earth life at all. In the entire history of the solar system, at most a handful of rocks may have made it from Earth to Europa. So it could be something else as well.

As those examples show, it could be very vulnerable. An RNA ocean say, or RNA only lifeform could perhaps become extinct after just a few years of exponential growth after the first contamination by Earth life throughout the entire ocean, especially if it is all connected and its ocean has food sources for the life to use. And however quickly or slowly it happens, there is no way we could reverse something like that once it got started. It would be the worst possible anticlimax to all our searches for life in our solar system, to know that Europa was such a biologically fascinating place, until the first probes from Earth landed there, and is no longer like that.

Until we know what's there, I think we have to treat every potentially habitable planet or moon or other habitat in our solar system as if it was the only one of its type in the solar system. Because a lifeform that evolves in Europa's ocean may well not evolve in Enceladus, or Ceres or on Mars or whatever place you study next. It could be our only opportunity for light years in every direction, to study such a lifeform.

• Perhaps they all have different unique lifeforms or types of pre-biotic life.
• Perhaps they all have almost identical independently evolved life (very surprising I think).
• Perhaps life from a previous star seeded them all or most of them.
• Perhaps only one of them has life, or none of them do.
• They are sure to have complex chemistry and we can learn from that also, maybe learn that life evolves only with great difficulty and find out what happens when it doesn't evolve too. We won't know until we find out.

As for experiments in Earth based life in space - we can do closed system habitats to try that out anywhere. For instance the Moon may have vast caves kilometers in diameter, so maybe we do it there. Or in free flying space habitats. There's enough material in the asteroid belt alone to create habitats with a total land area a thousand times that of Earth. There may be many opportunities to do that. We don't need to have as our first priority to turn everything into the closest possible approximation to Earth we can imagine, especially a very poor imitation of it, an ocean covered in kilometers of ice with the harsh environment of Jupiter's radiation on the surface, and too far from the sun for most photosynthetic life to be practical and not at all in its oceans (except for life that uses the heat radiation from hydrothermal vents for photosynthesis).

And meanwhile constructed habitats from asteroid materials can be designed with whatever environment you like, tropical gardens if you like, depending how much sunlight you reflect into it using space mirrors or solar collectors, or simulate conditions on Europa or Mars or other places in our solar system if that's your aim. Or you could simulate some the conditions on an interesting exoplanet. You can use spinning habitats with artificial gravity for whatever level of gravity you want, too.

That's looking forward a bit there - but only decades, centuries at most. You could build a Stanford Torus habitat within a decade or two with the funding and political will to do so even with present day technology. If we want to explore setting up habitats with Earth life in it outside of Earth, I think things like that would be the way to go - starting on a much smaller scale first probably. You could start with small exovivaria in LEO or on the Moon, and experiments with closed system recycling.

While there’s no way we can duplicate the billions of years of Europa’s history and the vast oceans larger than Earth’s oceans. If we mess it up, then the nearest “Europa” analogue may be light years away. And even then, chances are that if Europa and some Europa analogue both have life, even then most likely it has its own unique lifeforms, probably not even the same informational polymer in the place of whatever Europa has - not at all likely that it has the same lifeforms or proto life that evolved on Europa.

So why did they send a lander to Titan instead of Europa?

I think it might be partly that they were sending a spacecraft to the Saturn system anyway. In the case of the Jupiter system, then it’s much harder to visit Europa for more than a short time because of the ionizing radiation. Still you could do a penetrator with a fast flyby and that would work much like Huygens. It could communicate back to Earth during the flight to Europa and if it survived the landing, do some experiments and report back during its design life whatever it is.

But it would have many more planetary protection issues to work through than a Titan mission. I think myself it is best to wait for the orbiter mission first before we decide what to do next. We might well confirm the plumes on Europa and that would make it really easy to sample it’s ocean with a low flyby or orbiter and then we might not need a lander at all for the first missions there.

In situ instrument capabilities

During the Q / A, the team mention the idea of sending in situ life detection instruments to Europa in the future. We could use these on a flyby or a lander. So what instruments could we send? Actually there are many such already developed. Some of them have exquisite sensitivity, and could find life based on the minutest of traces, even able to detect a single molecule in the sample of biochemical interest.

Most of these instruments were developed for Mars. Whether they can be used as is for Europa, or need more modification, this shows the range of instruments we can send. I've no idea about the engineering challenge, to examine materials captured in an aerogel "in situ". One issue is to ensure that the readings are not confused by the material that makes up the aerogel so the composition of the aerogel is important. It also helps if you can do a slow flyby, so that there is less damage during impact into the aerogel. Anyway here are some of the instruments we can send, and some are exquisitely sensitive and would surely detect life if it is there.

I think if astrobiologists were asked, maybe in a competition to devise astrobiological instruments to send to Europa, they would rise to the challenge to devise instruments for a Europa flyby and you might get some surprises, neat ideas that you didn't expect. With the huge mass of the Europa missions on SLS, you could fly many of them - a lot of them are "labs on a chip" that weigh hardly anything.

Here are some ones that are already at quite a developed state, with an eye to eventually fly to Mars:

Rapid non destructive preliminary sampling

• Raman spectrometry - analyses scattered light emitted by a laser on the sample. Non destructive sampling able to identify organics and signatures for life. It's sensitive, can measure the distribution of the organics and other compounds by pointing the laser at different points on the surface - and is non destructive so it can be applied first before any of the other tests.

Detection of trace levels of organics and of chirality

• Gas chromatography - this is the idea used for the MOMA (Mars Organic Molecule Analyser). Used to analyse volatiles evolved from the soil samples in small ovens. Some of the ovens are filled with a "derivatisation agent" which can transform the chemical compounds into similar ones suitable for chiral analysis. They are then ionized and analysed with the mass spectrometer
• UREY, originally for ExoMars, with liquid extraction using high temperature, high pressure, sub critical water as a solvent (in case of Urey, between 100°C and 300°C at 20 MPa, or about 200 atmospheres, for several minutes) - under those conditions water has chemical properties similar to organic solvents. Urey is able to study the organics relatively unmodified
• Astrobionibbler - similar idea to UREY, smaller, later development. Able to detect a single amino acid in a gram of soil. Mass 2.5 kg.
• Planetary In-situ Capillary Electrophoresis System “lab on a chip” – separate the organics by ionic mobility, by electrokinetic methods in sub millimeter capillaries with the fluid manipulations done within the chip itself. Mass 3 kilogram, power consumption 2 watts.
• LDChip and Solid3,  also the Life Marker Chip developed for ExoMars but descoped, using monoclonal antibodies to detect organics. These detect a wide range of organics not specific to DNA based life. This instrument was tested in the Atacama desert and was able to detect a layer of previously undiscovered life at a depth of 2 meters below the surface in the hyper-arid core of the desert Mass for LMC was 4.7 kg, and for Solid3, under 7.5 kg.

Dallas Ellman fine tunes a component of the astrobionibbler. It uses ideas from the larger UREY instrument, using high temperature high pressure subcrtiical water as a solvent for non destructive extraction of organics. Now miniaturized to a "lab on a chip", low power requirments, low mass. During his summer internship at JPL in 2014, he helped discover and replicate the conditions the Astrobionibbler team needed to extract and detect amino acids from Martian regolith, so sensitive that it could detect a single amino acid in the sample. The target goal is a mass of 2.5 kilograms, a quarter of the mass of UREY. Astrobiologists have designed many exquisitely sensitive instruments that they want to send to Mars to do in situ searches for biosignatures. So far none have yet flown. UREY was approved for ExoMars but was descoped when NASA pulled out of the partnership.

Solid 3 - detects biosignatures using polyclonal antibodies. This version of it consists of a sample preparation unit weighing 5.5 Kg and a sample analysis unit weighing less than 2 kg. In tests, it's predecessor detected a previously undiscovered habitat two meters below the surface of the Atacama desert. Astrobiologist want to send this and other very sensitive instruments to Mars to search for minute traces of degraded ancient organics from life and for present day life which is also likely to be hard to detect in such hostile conditions. Some are tiny labs on a chip - instruments that a few years ago filled an entire lab and now can be miniaturized to a single chip. These in situ searches could be confused by the minutest traces of organics from Earth brought by astronauts.

An earlier version of the same technology, the Life Marker Chip, mass of 4.7 Kg, was approved for ExoMars but later descoped.

Direct search for DNA

These can detect life on Mars if it is DNA based so related to Earth life. As DNA sequencers, they can sequence the entire genome of any lifeform found.

• Miniaturized DNA sequencer could work if we had a common ancestor right back to the very early solar system whenever DNA first evolved. This is in a reasonably advanced state. They say it could be ready to fly by 2018.

Electron microscope

• Miniaturized scanning electron microscope. This can’t detect whether it is life or not, but is useful along with the others.

Search for life directly by checking for metabolic reactions

These can detect life even if it doesn't use any recognized form of conventional life chemistry. But requires the life to be "cultivable" in vitro when it meets appropriate conditions for growth.

• Microbial fuel cells, where you check for redox reactions directly by measuring the electrons and protons they liberate. This is sensitive to small numbers of microbes and has the advantage it could detect life even if not based on carbon or any form of conventional chemistry we know of.
• Levin’s idea of chiral labeled release, where he has refined it so you feed the medium with a chiral solution with only one isomer of each amino acid. If the CO₂ is given off when you feed it one isomer and not with the other, that would be a reasonably strong indication of life.This has the advantage that the life just needs to metabolize amino acids, and to produce a waste gas that contains carbon (such as methane).

There are many instruments like this we could send, and several of them are already space qualified but never flown.

Optical microscopy

I also wonder about an optical microscope. Why not send, not just a "geologist's hand lens" but a diffraction limited optical microscope? With resolution of 200 nm. It could tell us things about the behaviour and structure of micro-organisms or protocells we might not be able to find out by other methods. 

Ideally you want to see the structure of protocells if they exist, and other sub-optical limit structures, so I do wonder also about the microscopes that go beyond the diffraction limit, but I'd have thought they are probably too complex to send into space? Probably won't verify life or protolife unless it is actually still viable and active. But could give interesting data in combination with the other instruments.

What if we get ambiguous results from Europa just as we did for Viking?

Yes we might well get get ambiguous results. That's how science works. But if we are so scared of ambiguous results that we never fly anything unless we are sure it will give a clear cut result - surely that's going to slow down the pace of discovery? I think that the natural response to the ambiguous Viking results was to do a follow up experiment such as the labeled release, to find out what happened. If we'd sent such an experiment, say, on Sojourner, it would have weighed very little and we'd now know for sure if Viking found life or not, and there'd be no more discussion about it, either way.

The safest approach is to search for things you know you can discover, with proven instruments you have already sent into space. And it is natural for mission planners to want to do that as it is the least risky thing to do. But you may be missing out on new discoveries that perhaps could be made easily with different instruments.

Null and ambiguous results are important. If you send a DNA sequencer to test for DNA - well it is one hypothesis that Europan life could be related to Earth life through cells from before the origins of our solar system. If you find other indications that may indicate life, or strongly indicate it, but no DNA that's a significant null result. Based on that one can decide what to fly in the next mission for a follow up. If you get ambiguous results from an experiment that is expected to decide the question - that shows there is something interested and unexpected going on. It might even be more interesting than the thing your experiment was designed to test for.

Europa is only two years travel time from Earth via fast Hohmann transfer, and by the 2020s we may have more heavy lift capabilities that will make it easy to send follow up missions to resolve the questions that early missions raise.

As well as all that - just sending the instruments at all gives exobiologist experience in sending their instruments in space, which then become space rated for future missions, so adding to exobiology experience. If the DNA sequencer gives a null result for Europa, still, it's now space rated, and you can fly it to Ceres, say, if we find habitats on Ceres, or to Enceladus, and indeed to Mars.

Also the process helps inspire a whole generation of astrobiologists, to see their instruments fly in space. At the moment only geological instruments have flown, apart from the very early Viking instrument. You have to start somewhere with the astrobiological in situ searches.

See also

• See also my "Super Positive" Outcomes For Search For Life In Hidden Extra Terrestrial Oceans Of Europa And Enceladus (goes into the search for life and possible scenarios in more detail. The life detection instruments section above is from there).
• You might be interested in the facebook group: Search for ExtraTerrestrial Life - Europa&Enceladus + Subsurface Oceans
• See also my As Philae Awakes - Where Might Life Hide In Our Solar System?

Part of this article originated as my answer to If there is a possibility of life on Europa, then why did NASA land a craft on Titan and not Europa? on Quora

Other places in the solar system - Titan, Triton, Io, etc

So, now let's look further afield at some of the other places in the solar system that life could be found, or prebiotic chemistry. Most of these are places where the conditions are so different from Earth life that there may be no issue at all even sending human beings to do in situ searches there, once we have that capability. An international committee of scientists, COSPAR, meets every two years to discuss issues to do with planetary protection amongst other things. They publish the results using a classification scheme, described in detail in the wikipedia article on Planetary Protection:. So let's just quote from that article (Actually I'm the main author of this section of it).

Planetary Protection classifications

Category I

“not of direct interest for understanding the process of chemical evolution or the origin of life.” 

• Io, Sun, Mercury, undifferentiated metamorphosed asteroids

Category II

… where there is only a remote chance that contamination carried by a spacecraft could jeopardize future exploration”. In this case we define “remote chance” as “the absence of niches (places where terrestrial microorganisms could proliferate) and/or a very low likelihood of transfer to those places.”

• Callisto, comets, asteroids of category P, D, and C, Venus, Kuiper belt objects (KBO) < 1/2 size of Pluto.

Provisional Category II

• Ganymede, Titan, Triton, the Pluto-Charon system, and other large KBO's (> 1/2 size of Pluto) Ceres,

Category III / IV

“…where there is a significant chance that contamination carried by a spacecraft could jeopardize future exploration.” We define “significant chance” as “the presence of niches (places where terrestrial microorganisms could proliferate) and the likelihood of transfer to those places.”

• Mars because of possible surface habitats.
• Europa because of its subsurface ocean.
• Enceladus because of evidence of water plumes.

Category V

Unrestricted Category V: “Earth-return missions from bodies deemed by scientific opinion to have no indigenous life forms.”

Restricted Category V: "Earth-return missions from bodies deemed by scientific opinion to be of significant interest to the process of chemical evolution or the origin of life."

In the category V for sample return the conclusions so far are

• Restricted Category V: Mars, Europa, Enceladus.
• Unrestricted Category V: Venus, the Moon.

with others to be decided.

There may be issues though with the Venus clouds. As you see from that list, they were classified by COSPAR in 2006 in the same way as the Moon, so that you only need to document what you did when exploring them, and sample return was also classified as for the Moon, so no precautions are needed. However some astrobiologists challenge this classification and think it needs to be revised.

Callisto and other places with subsurface oceans not connected to the surface.

Callisto is thought to have a subsurface ocean now, like many of the ice moons. But it's classified as category II, "ere there is only a remote chance that contamination carried by a spacecraft could jeopardize future exploration”

That's because they think there is no connection between its subsurface ocean and the surface. It's got a cratered surface with no sign of any modification. Callisto could be a valuable stopping point for humans in the outer solar system. It's just outside the hazardous radiation belts of Jupiter, so an ideal place to stay while studying the Galilean moons and has plentiful ice.

So, there is no problem at all sending humans to Callisto. However if they want to study its subsurface ocean they would have to drill deep. The ocean, if it exists, is at least a few kilometers thick and is less than 300 kilometers below the surface. Also not too likely to be habitable.

It's ocean might have life. It's probably salty. But it's only heated by radioactive materials in Callisto's core so wouldn't have the energy flux of the Europan ocean which is heated by tidal heating as well. This possibility was first announced in Nature in october 1998

Life in liquid ("supercritical") CO₂

This first habitat is unusual because it is an "extra terrestrial" type habitat that's actually accessible here on Earth, yet we know little about it to date. It's also probably present in other places in our solar system, particularly on Mars, and (not so easily habitable), on Venus too.

We are used to CO₂ as "dry ice" which turns instantly into a gas when it is heated. But, did you know that CO₂ is liquid under high pressures and at normal temperatures? You can actually find liquid CO₂ in its natural state on Earth, at the high pressures of the ocean depths. Indeed if you explore the oceans, then anywhere below around 0.8 kilometers below the ocean surface,, CO₂ is a liquid. This video is taken at a depth of 1.6 kilometers at a white smoker vent system on one side of the small undersea volcano Eifuku off Japan

The "bubbles" in this video are in fact bubbles of liquid CO₂. And there's life there, not actually living in the bubbles but apparently not bothered by it at all. See "Life in liquid carbon dioxide". The first discovery of natural liquid CO₂ in the oceans goes back to 1990. Interestingly, as you raise its temperature, liquid CO₂ at around 31.1°C, and 73.8 atmospheres in pressure becomes a supercritical fluid. That's a phase where the distinction between a gas and a liquid disappears. Often the properties change also.

Table from the paper Supercritical Carbon Dioxide and Its Potential as a Life-Sustaining Solvent in a Planetary Environment by Ned Budisa and Dirk Sculze Makuch

This is important for habitability. CO₂ at these temperatures (above 31.1°C) and pressures (above 73.8 atmospheres), is actually a solvent like water. Indeed, the researchers Ned Budisa and Dirk Sculze Makuch found that it has advantages over water for life processes. Enzymes are more stable in liquid CO₂ than they are in water, and it makes enzymes more specific about the molecules they bind to. This supercritical liquid CO₂ is often used for sterilizing, because of its affinity for organics. However, some microbes and their enzymes can tolerate living in it. This was a very surprising recent discovery reported in February of this year. The researchers found six strains of microbes, isolated from three sites targeted for geological carbon dioxide sequestration - that have the astonishing ability to grow on the interface between water and supercritical CO₂. See Microbial growth under supercritical CO₂.

There are fairly large reservoirs of liquid CO₂ beneath the Earth's oceans. For instance a CO₂ lake found off the coast of Taiwan at a depth of 1.4 kilometers.

At that depth, liquid CO₂ is lighter than water. That is how they found it through the rising bubbles of liquid CO₂  rising through the sea water. For this to work, most of it must be kept in place somehow or the whole reservoir would empty. In this case they think it is probably trapped by an overlying layer of clathrates, because they observed clathrates. They found life there, even in low numbers within the liquid CO₂ layer itself. In this case, the liquid is below the temperature at which CO₂ is supercritical.

Below a depth of around 3 kilometers, CO₂ becomes heavier than water. There probably are large reservoirs of liquid CO₂  below that level in the floor of our oceans, but they would be harder to detect, as no bubbles would escape from them. So - do these reservoirs exist? Are any of them warm enough for supercritical CO₂? And if so, are they perhaps inhabited by novel forms of life? That's a lot of "if"s but it's fun to think that we could possibly have life as novel as that even on our own Earth, and if so, we wouldn't know yet.

You get supercritical CO₂ on other planets too. Indeed the whole of the Venus atmosphere is supercritical at ground level and for a short way above. However - it's not a likely place for life. It's too hot for organics to be stable. As well as that it's more of a gas than a liquid at those temperatures. That's because it is below the "Frenkel line" - the line above which a supercritical fluid has more liquid like than gas like properties.

Diagram from Structural Evolution of Supercritical CO₂ across the Frenkel Line

However it may have a layer of supercritical liquid CO2 a short way below its surface, and in the past, when Venus's atmospheric pressure was probably several times higher (getting into the hundreds of bars), and the temperatures cooler, it might have had supercritical liquid CO₂oceans, which might have flowed like a fluid and carved out some of the features found on the surface.

You don't need a thick atmosphere or oceans for pressure though. Surface ice and rock layers would also lead to layers of liquid CO₂, and this could happen on Mars. Liquid CO₂ would be stable on Mars beneath about 100 meters of rock in the cold conditions there. At one point this was the favoured explanation of the Mars gullies as many of them start at a depth of about 100 meters below the top of the cliff. Combine those conditions with high enough temperatures, say from hydrothermal heating, and again you would have supercritical CO₂ on Mars. Which might be a habitat for an exotic form of life.

Life in atmospheres of gas giants

This is an idea suggested by Carl Sagan in his Cosmos series.

For Carl Sagan's scientific paper on this, see Particles, Environments and Possible Ecologies in the Jovian Atmosphere.

And more recently by Stephen Hawking in his "Into the Universe"

In Cosmic Biology: How Life Could Evolve on Other Worlds, Louis Irwin and Dirk Schulze-Makuch look at this idea in some detail. First they note that the upper layers with the visible clouds on Jupiter seem to be too cold for liquid water. Lower down, where the temperatures are warm enough, then there is little water. See page 166. They thought it unlikely that Earth life could survive there, not being pre-adapted to the conditions. That's why, Galileo at the end of its mission was sent to crash into Jupiter, for planetary protection reasons, and it's also why Cassini will be sent to crash into Saturn. The idea is that Earth life can't survive in either of the gas giant atmospheres, and by doing this we avoid the possibility of contaminating the interesting moons of these giants with Earth life.

However, what about life based on different principles from Earth life? The main problem in that case, for Carl Sagan's gas creatures, is how the life could evolve there in the first place. There are trace amounts of hydrocarbons, nitrogen compounds, and sulfur complexes. But there's a lack of oxygen. Also, there's no mechanism for concentrating the organics into one place. Any region where life could form is liable to be torn apart by the strong winds, and turbulence, and affected by strong radiation. They thought that the conditions there could lead to complex organics forming structures made up of large scale chemical networks of life precursors. But without a hard and fast physical boundary or exact replication, then it couldn't develop to the next step and would not fit the criteria to count as life.

They did find a way that the gas giants could have life though, and that is if the gas giant atmospheres could be seeded by life from their own planetary moons, such as Io for Jupiter, and Titan for Saturn. Unlike Earth life, this life may be similar enough in chemistry to the planets for their life to survive there. In case of Io, which could seed Jupiter, it would be pre-adapted to radiation and very low temperatures and to a sulfur based chemistry that could be found in the Jupiter atmosphere. And in the case of Titan, which could seed Saturn, it would be adapted to a dense, cold, organic atmosphere, again conditions that could be found in pockets in the Saturn atmosphere.

For details see page 168 of their book, most of which is available online.

Supercritical liquid hydrogen layers in gas giant atmospheres

Another possibility is life at a much lower level in the gas giant atmosphere. At high enough pressures, hydrogen becomes supercritical, and, like liquid CO₂, it becomes a solvent for organics. On Jupiter this zone is very narrow but on Saturn then it is quite wide. This is suggested as a possibility in The Limits of Organic Life in Planetary Systems which was produced by the Space Studies Board.

Life in liquid nitrogen - Pluto or Triton

This photograph of Neptune's largest moon Triton shows dark streaks thought to be nitrogen geysers.

Triton's south polar terrain photographed by the Voyager 2 spacecraft. The dark lines are the trails of plumes from volcanoes, thought to be caused by eruptions of liquid nitrogen from below the surface. Some of the plumes were actually observed erupting during the flyby- by anaglyph projection, which made them easy to pick out as they were closer to the spacecraft than the other features.

Triton - and perhaps Pluto also - could have thin layers of liquid nitrogen, between a surface of solid nitrogen ice and a subsurface of water ice. One researcher Jeff Kargel suggested that Pluto could have rivers of liquid nitrogen or neon. If not on the surface, it could flow below the surface since solid nitrogen is "a fantastic insulator". So could there be life in these layers of liquid nitrogen? Liquid nitrogen would be a non polar solvent (there is no separation of charge in its molecules), which means it can't dissolve organics (which are polar). But it might be just the thing for polysilanes, a complex molecule that uses silicon in the place of carbon. Maybe Triton and Pluto could have silicon based lifeforms?

It turns out that silanols - a kind of silicon version of alcohol - can dissolve in liquid nitrogen. And - in these conditions, silicon has as diverse a chemistry as carbon, as William Bains has argued in his hypothesis paper Many Chemistries Could Be Used To Build Living Systems. The silanols have weaker bonds than carbon based organics - but this is just the thing you need in very cold conditions.It's "silicon based life" but not in the sense that rocks are made of silicon - any more than humans are diamond or graphite or charcoal based life. The silicon of course is combined in long chains with many other atoms. See also Peter Ward's chapter on this idea.

Life in the oceans of Titan

Saturn's moon Titan is, so far, the only known place in the solar system with liquid water on its surface apart from Earth. Most of the lakes are around the north pole, with one lake, lake Ontario, at the south pole.

 
Glint of sunlight on the lake region around the northern pole of Titan.

Here is Chris McKay talking about prospects of life in the Titan lakes

He mentions there the provisional observations of hydrogen and acetylene and ethane depletion near the surface of Titan, which they'd predicted as a possible sign of life on Titan.  Also he mentions that oxygen would be in short supply, and need to be extracted from water ice "rock" by microbes. This is related, a possible way that life on Titan could make cell membranes without use of oxygen.

Possible oxygen free cell structure made of organic nitrogen compounds that could function at the low temperatures of Titan's ocean.

Titan is the only place in the outer solar system which we have sent a lander to, the Huygens probe. Sometime maybe we will send some more probes there to explore it further. This was a recent idea for a submarine to explore Titan:

See also Life on Titan (wikipedia).

This is such an extreme habitat, that it seems first of all, impossible that Earth life could survive there. You could land humans on the surface of Titan - and in some ways it might be one of the easiest places for us to live, as suggested by Charles Wohlforth and Amanda Hendrix, authors of Beyond Earth: Our Path to a New Home in the Planets. Their idea is described in brief in Let's Colonize Titan in the Scientific American. Some of the advantages are:

• Atmosphere at the same pressure as our Earth's atmosphere. Your spacesuits wouldn't need to be pressurized. They would of course have to be insulated from the cold, but they would be much more flexible, without the enormous outwards pressure of tons per square meter needed in vacuum conditions. You could build conventional houses too, equal pressure inside and out. They would only need to be air tight.
• Protection from cosmic radiation by the atmosphere
• Plenty of ice for water.
• Earth life would probably have no impact on any Titan life
• Abundant resources for making plastic which could be used to make housing. So easy to construct, with just a thin covering to keep out it's atmosphere, equal pressure inside and out - so like the Venus cloud colonies, you could have huge internal spaces filled with oxygen and nitrogen for very little by way of mass
• Terminal velocity a tenth that on Earth so if you fall out of a plane, no problem.
• Human powered flight - could fly in the light gravity

You still need to think about whether molecules from Earth life such as RNA and DNA could be incorporated by Titan life. Also, whether organics from a human occupied habitat would confuse the search for life there, if the life is elusive.Also, though it's easy to see that Earth life couldn't survive on Titan except in cryovolcanoes - can we be sure the other way around, that Titan life can't survive on Earth or in human occupied habitats? It seems unlikely that life adjusted to those habitats could survive here. But what if the Titan life evolved from previous life that first originated in its deep subsurface oceans? Is there any chance it could retain capabilities that would let it survive as spores, and then maybe reproduce in oil deposits or in some other way survive in the much hotter conditions of Earth? It seems unlikely, but can we rule it out before we know what is there?

Also, Titan probably has a subsurface ocean. If so, if there is communication between the subsurface and the surface, e.g. cryovolcanoes with liquid water in place of lava, then that's an obvious contamination issue for the subsurface oceans. Titan is currently categorized as "Provisional category II" with "only a remote chance that contamination from Earth could jeopardize future exploration" - the same as our Moon. But it is provisional because they say that more research is needed. Other places categorized as provisional category II are Ganymede, Triton, the Pluto Charon system, Ceres and the larger kepler belt objects (up to half the size of Pluto).

It would surely be studied robotically first so you'd know all that before you land humans there..

Sulfur based life on Io

There might be life on Io, sulfur based, in underground pools of liquid SO₂, with the life chemistry probably also using H₂S, because, though less abundant, it forms hydrogen bonds easily, and is more suitable for a solvent within the cells. So life might seek out the liquid H₂S and use this as their intercellular solvent, while living in pools of the more abundant liquid SO₂.

Volcanoes erupting on Jupiter's inner most moon Io, photographed by the Galileo spacecraft. The surface is rich in sulfur, and one suggestion is that Io could be host to an exotic sulfur based biochemistry.

Louis Irwin and Dirk Schulze-Makuch explore this in some detail in Cosmic Biology: How Life Could Evolve on Other Worlds, The life molecules would have backbones of sulfur, nitrogen, phosphorus and other elements and would take advantage of the complex chemistry of sulfur compounds. Sulfur has a wide variety of oxidation states, even fractional oxidation states such as -0.4 or -2/3. It also forms a variety of ring compounds, and polymers.The temperature range over which H₂S and SO₂ are both liquid is quite narrow, from -75°C to -60°C. And because these temperatures are quite low, the reaction rate is likely to be slower.

A plume ejected from same general region as one of the regions imaged by Voyager, called Masubi, it erupts 100 km into space from Io. The eruption comes from different places in this region and leaves plumes of SO2 on the surface.

Louis Irwin and Dirk Schulze-Makuch say in their concluding section of this chapter:

"It would be all underground and able to thrive only when temperatures reached an appropriate narrow range. But that would happen, for at least a brief period, in local pools or over short stretches of ground, every time a hot spot erupted or a sheet of lava advanced."
in Cosmic Biology: How Life Could Evolve on Other Worlds - Chapter 9, Fire and Ice (not available online).

Io is classified as category I, no problems of planetary protection at all. It would be a hazardous place to land humans because of the high levels of ionizing radiation from Jupiter. But it seems unlikely that Earth microbes could be harmful to any Io life, if present, and it's not likely in the other direction either, that any putative Io life could harm Earth.

What about life in lava flows on Venus?

One of the most challenging forms of life would be silicon based life living in liquid lava. If this was possible, we might find it on Venus - which has entire river channels that travel for huge distances across its surface.

The arrows show the two ends of this section of Baltis Vallis on Venus - the longest known channel of any kind in the solar system, total length of 7,000 kms. Though there is no liquid in it now, it may have been carved out by rivers of liquid lava, which, if not too hot, might have been a suitable place for life that relies on silicones.

These could use Silicones - organosilicon polymers with a silicon-oxygen backbone. These are stable at temperatures so high they would destroy any organics. But - would they remain stable at the temperatures of even cooling magma pools on Venus? That's the big question. Unlike water chemistry which is easy for us to explore in our laboratories - it's not so easy to explore the chemistry of silicones in magma pools.

Venus has no continental drift so doesn't have volcanoes all the time as Earth does - instead its entire surface may "turn over" every few hundred million years. But it shows signs of "young" features and may still be geologically active.

Recent observations show that some parts of the Venus surface may still be active today, with hot spots that appear and disappear, perhaps pools of lava, superheated rocks, or plumes of hot gas.If life is possible in magma pools - then why hasn't it evolved on the Earth also? Why have we never found silicon based life fossils in lava flows on the Earth? Silicon life seems unlikely to us. But is it just that it is a low probability life form? After all - for all we know organics based life, evolving in oceans, might also be low probability.

Maybe, just as we have no silicon based life in our lava, as far as we know - maybe, on other planets, there's no water based life in their water. Maybe on other planets there are silicon based life forms reasoning in the same way that we do, that carbon based life is impossible. Perhaps those silicon based life forms, if they exist, living in molten magma have lifeless seas of water, just as we have lifeless flows of lava (as far as we know anyway). To them, water might well seem too cold to sustain life which they think can only occur at the temperatures of molten lava :).

Life in clouds of Venus

The idea here is that Venus started off Earth like in the early solar system. But at some point it dried up, lost its ocean due to a runaway greenhouse effect, which didn't affect Earth in the same way because continental drift on Earth continually buries and circulates the carbonates. Though the surface of Venus is amazingly inhospitable, the layer at the top of its clouds is in many cases the most habitable location in our solar system after Earth - almost Earth like in temperature, pressure, and atmospheric composition (without the oxygen of course). It has one major drawback, droplets of concentrated sulfuric acid.

However we do have acidophiles on Earth that survive in conditions not far off the acidity of Venus clouds - in sulfuric acid outflows from mines on Earth. The UV light at the cloud tops could be hazardous also, but the life in the Venus clouds could be protected by pigments or by an external layer of solid sulfur (the allotrope S8). So - it's possible that there is sulfuric acid tolerant life in the Venus clouds. The other main problem with the high Venus clouds is that there are no solid surfaces of course. But it could have evolved in the early solar system and then migrated to the clouds as the surface got drier and hotter.

The main question is, could the life find some way to stay aloft? The residence time of particles is months rather than days - so - that makes it easier, and turbulence could return some of the life to the tops of the habitable layer after it reproduces - but it's still quite a challenge.The surface of Venus is totally hostile to Earth life, a dim, hot furnace, with temperatures well over 400°C. But conditions are different at the Venus cloud tops. Temperatures are ideal, with plenty of light. There are several factors that suggest life may be possible there:

• The atmosphere is not in chemical equilibrium, with H₂S and SO₂ present together, also oxygen and hydrogen, which life could use as a source of energy.
• Detection of carbonyl sulphide (OCS) - a clear sign of life here on Earth (though it could be created inorganically on Venus, by volcanoes), and the levels of H₂S are also higher in the upper atmosphere, a suprrising result which might mean it is produced by some process in the upper atmosphere rathre than from volcanoes, possibly by life.
• Doesn't have the expected concentrations of carbon monoxide. That could be a sign that life is using the CO for its metabolism. On Earth, 450 strains of photosynthetic bacteria rely on carbon monoxide for their carbon. Schulze-Makuch suggests that they could be combining carbon monoxide with sulfur dioxide and possibly hydrogen. The anoxic acidic envieronments in the Venus clouds are similar to those in the hydrothermal vents in some ways. See http://www.astrobio.net/news-exclusive/venusian-cloud-colonies/
• Atmosphere super rotates giving a day night cycle of a total of 4 days making photosynthetic life easier because the night is shorter than the 117 day cycle on the planetar surface
• Continuous presence of thick clouds more stable than those of Earth, with water present in the form of sulfuric acid in the clouds - this is the region of the Venus atmosphere with most water present.
• It takes more than 200 days for a 1.1 micron particle to fall out of the clouds , which is more than enough time for several generations even of rather slow growing microbes, to reproduce and form spores ( page 10 of Charles Cockell's Life on Venus. ) ,
• Most of the ingredients of life are easily accessible in the atmosphere. Five of the six main elements life needs, hydrogen, oxygen, carbon, nitrogen and sulfur are present in large quantities . The main limitation on life similar to Earth life may be the requirement for phosphorus which is present in trace quantities. Chlorine is present in low qunatities. Calcium, potassium, sodium, mangesium and iron are not yet detected though they are likely be present in the form of dust since surface rocks include MnO, MgO, CaO, Na₂O,K₂O,FeO, TiO₂ and SiO₂ - See Geoffrey Landis's Astrobiology: The Case for Venus and page 10 of Charles Cockell's Life on Venus.
• Detection of particles which are non spherical like microbes and the right size for them. This was a rather surprising discovery, as there is no obvious vapour source that would condense as particles of this size and shape. Some scientists have suggested that these large particles may be a result of miscalibration of the equipment, with the conclusion: , "This allows a simple understanding of the source of all the cloud particles, but at the cost of disbelieving some of the measurements.". .However others say that there is good evidence that the equipment was operating under nearly optimal health conditions. This is the "Mode 3 particle controversy", for details of the controversy see section 4.2 of this paper.
• Detection of dark streaks in the atmosphere of unknown composition which absorb UV. The absorption spectrum is broad without distinct peaks which suggests it is due to particles or droplets rather than gas, Could this be due to absorption of the UV by life either to protect itself or for photosynthesis or both?

Of those, the three main lines of evidence which just possibly could indicate the presence of life are the UV absorption (possible photosynthesis or UV protection), the chemical disequilibrium, especially the presence of OCS, and the possible presence of large non spherical particles. All of these could also be due to non life processes but are not easy to explain in that way.

For more on this:

• Venusian cloud colonies (NASA astrobiology magazine),
• Astrobiology: The Case for Venus
• Life on Venus
• Could dark streaks in Venus' clouds be microbial life
• Could there be life in the clouds of Venus?
• Acidic clouds of Venus could harbour life

If we do find life there, it probably didn't originate in the cloud tops. Instead, it's probably a relict of surface life in the early solar system, which migrated to its upper atmosphere as the conditions became harsher. (See also section on Venusian clouds in "Cosmic Biology - How Life could Evolve on Other Worlds").

Artist impressions of Venusian clouds, credit ESA. The surface of Venus is utterly hostile to Earth like life, at temperatures of well over  400°C is. It is also dim, not much light filters through the clouds. But high in the atmosphere above the cloud tops, then conditions are far more conducive to life, at temperatures around  0°C. The cloud droplets themselves are the main challenge, concentrated sulfuric acid, with acidity similar to battery acid.  There are intriguing signs that just might indicate life, in the upper atmosphere though they can also have other interpretations.

Venus probably started off similar to Earth. It's surface actually gets less light than the Earth, because though closer to the sun, it has highly reflective clouds. It is so hot, not so much because it is closer to the sun, but because of a runaway greenhouse effect. Earth has similar amounts of carbon dioxide locked up in limestone, and could look the same in the future as the sun heats up further. Most scientists think that Venus was a near twin of Earth in the early solar system, with oceans like Earth. We don't have quite the same confidence about this that we have for Mars because its entire surface was resurfaced a few hundred million years ago which would erases any clear signs of the ancient oceans such as the deltas and shore lines of Mars. But there are still hints that suggest it did have them.

Evidence for early oceans on Venus is indirect.

This is a temperature map of Venus. Observations from orbit are consistent with the idea that Venus had earlier oceans, with suggestions that it might have granite land masses. If so these may be the remains of ancient continents

"The eight Russian landers of the 1970s and 1980s touched down away from the highlands and found only basalt-like rock beneath their landing pads. The new map shows that the rocks on the Phoebe and Alpha Regio plateaus are lighter in color and look old compared to the majority of the planet. On Earth, such light-colored rocks are usually granite and form continents.

"Granite is formed when ancient rocks, made of basalt, are driven down into the planet by shifting continents, a process known as plate tectonics. The water combines with the basalt to form granite and the mixture is reborn through volcanic eruptions. If there is granite on Venus, there must have been an ocean and plate tectonics in the past," Nils Muller said.
See Oceans on Ancient Venus - Study suggests (space.com)

This life could also survive in high pressure subsurface habitats with supercritical liquid water.

If Venus did have oceans in the early solar system, life could have evolved independently from Earth. Or, it's possible that Venus was seeded by life from Mars or Earth, billions of years ago. Or the other way around, it could have seeded Earth or Mars, or both. If so then this is a really exciting possibility for biology. We may make amazing discoveries from studying life that's been isolated from Earth for billions of years, or possibly evolved independently.

Venus (left) may have had oceans like Earth (right) in the early solar system, and life could have evolved there, or been seeded by Mars or Earth. If so it might still exist in the clouds.

However this may also have planetary protection implications. Some time back, in 2006, an international team of scientists for COSPAR (Committee on Space Research) examined the situation for Venus, in "Assessment of Planetary Protection for Venus Missions" (you might find that the easiest way to read this report online is to get free membership of NAP and then use the download button and read it as a pdf). They came to the conclusion that even in the Venusian cloud tops, conditions are so different from Earth conditions that there is no need for planetary protection. As a result of this report, Venus is currently classified as Category II, and sample return as unrestricted Category V. This means that you simply need to document whatever it is you do.  (For the current planetary protection categories, and policies, see Planetary Protection (Wikipedia) )

This also means that you can return a sample of the Venus atmosphere to Earth for study, with no need to contain it or act in any way to protect the Earth environment. The only requirement is that you have to keep detailed documentation of whatever you do. However, there was a dissenting voice at the time, by Dirk Schulze-Makuch who was not part of the team. See Planetary Protection Study Group Mulls Life On Venus

Everyone seems agreed that there are no planetary protection issues for the Venus surface, with temperatures well over 400C. But should the Venus atmosphere perhaps be re-categorized as category III, meaning that you have to sterilize spacecrafts that visit it? Should sample return from Venus be re-categorized as restricted Category V, meaning that you have to take precautions to protect Earth in event of a sample return?.

Some of the material here comes from my article If there is Life in Venus Cloud Tops - Do we Need to Protect Earth - or Venus - Could Returned XNA mean Goodbye DNA for Instance?

Possibility of earth life able to survive in the Venusian clouds

At first sight it certainly seems unlikely that Earth life could survive in the concentrated sulfuric acid droplets in the clouds. These droplets have pH less than 0, similar to battery acid. This is the main reason the COSPAR team gave for their conclusion that no Earth life could survive in them. However, in 1991 researchers found some Earth microbes able to survive sulfuric acid with pH 0 or lower, close to the Venus cloud top conditions. These researchers also wrote that it is  possible that we might find organisms able to tolerate even lower pH levels. Their most acidophilic (acid loving) microbe was  Picrophyilus, which grows optimally in sulfuric acid at pH 0.7 and is capable of growth (not just survival but growth) down to pH -0.06 (1.2 M sulfuric acid). This is a microbe which you can find living naturally in highly concentrated sulfuric acid in the wild, in acid mine drainage and in solfataras (sulfur emitting fumaroles).

So perhaps some Earth micro-organisms could live there after all. Only 1% of the bacteria on Earth can be readily cultivated in culture media. There are various reasons why this might be the case. See Strategies for culture of ‘unculturable’ bacteria for an overview.

The "Great Plate Count Anomaly" - if you cultivate cells in a medium and count the number of Colony Forming Units (CFU's), and if you then take the same sample and count individual cells in a  high powered optical microscope, typically you find that there are about 100 times as many cells as you detected with the CFU method. This is because biologists currently can only cultivate 1% of living cells, typically.

Also, only a tiny percentage of all species have been studied in any detail. So it is hard to say for sure what the capabilities are of the micro-organisms we haven't yet studied, such as the majority of the archaea. This is the issue of "Microbial dark matter". For instance a recent study found that - "Of the 100 major branches, or phyla, of microbes, less than one-third have any described species", see How Many Microbes Are Hiding Among Us?

The microbes carried by humans can have hidden extremophile capabilities - because microbes do not lose their capabilities, usually, when they move to a different environment. Some are polyextremophiles able to live in a variety of extreme environments as well as in much more ordinary ones (for humans). A typical human has 100 trillion microbes in 10,000 species - and the species mix varies from one person to another. Many of these will be unknown to science, and some may well have extremophile capabilities. For example a recent study of microbial populations of human belly buttons found a couple of species able to thrive in extreme cold and extreme heat. Another example is the discovery of a microbe on a human tongue able to thrive in conditions of very low pressure.

Possibilities of indigenous life in the Venusian clouds

The other way then there have been suggestions of possibilities for life in the Venus clouds, indigenous life. There are one or two interesting hints, observations that could be interpreted as evidence of indigenous life. The most intriguing of these are, the presence of OCS which on Earth would be strong evidence for life. On Venus however it is just suggestive, not conclusive. There are processes that could create the observed levels of OCS without life, and detailed models of these processes are compatible with the observed levels. The atmosphere is also not in equilibrium, as it has both H₂S and SO₂. This disequilibrium is something that life could exploit. The upper atmosphere of Venus also has been shown to contain particles that are microbe sized, and non spherical, which might be an indication of life in the clouds. Particles in the Venus atmosphere stay suspended for months, rather than the days for Earth. Still, they will eventually fall to the lower layers; so that makes it an issue, how do the microbes stay aloft? 

I haven't yet seen a worked out answer to this, so here are a couple of suggestions to explore. First, perhaps microbes in one droplet, descending, could send out spores (explosively perhaps) that land in other droplets that ascend, and so continue the reproduction?

Another idea is based on the observation that some microbes form gas vacuoles on Earth more or less permanent, They are used by cyanobacteria to regulate buoyancy in water, not that far off the idea of using hydrogen vacuoles to regulate buoyancy in CO₂, evolved over billions of years. Is it possible I wonder? The main difference is, that the gas vacuoles in cyanobacteria take up only a small part of their bodies (and are made up of smaller, rigid, gas vesicles). Apparently Anabaema has gas spaces occupying up to 9.8% of their volume (see page 124 of the paper "Gas vesicles"). But this is far below the levels needed for the Venus atmosphere.

Gas vesicles. These are filled with ordinary air, and are used by cyanobacteria to regulate buoyancy in water, several of these cluster together to make a gas vacuole. The gas can occupy to 9.8% of the volume of the microbe.

The vesicles would need to be filled with hydrogen instead of air. Then with the density of CO₂ of 0.001977 (and hydrogen, 0.000089) compared with water, at 0°C, they would still need to have so much hydrogen in the vesicles that they occupy approximately 98% of the volume of the microbe. I'm not sure if this is possible. However, life solutions are often surprising.

If we do find life in the Venus upper atmosphere, then we would need to find out next, how it managed to stay there and reproduce. For instance, could the cells provide hydrogen filled bubbles, or external vesicles filled with gas, which remain attached to their bodies, somewhat like the bubble nests created by some insects, and use those to float in the Venus atmosphere? Or, very speculatively, indeed might there even be higher plants or animals that do this in the Venus atmosphere?

Froth of Spittle Bug, or Frog Hopper - Larval form - could a similar technique be used in the Venus cloud tops, using bubbles filled with hydrogen, attached to the microbe or higher life form as a type of froth or foam, for buoyancy?  It would need to have less than 98% of the volume for the bubbles and the body of the creature, with the rest all hydrogen, to float at the 1 atm level on Venus. 

This idea that Venus cloud life could use hydrogen for buoyancy is my own suggestion. I've not seen it published anywhere. Do say if you know of anyone who has published a paper exploring it, or any research into it.

The main questions still unanswered for planetary protection for the Venus clouds

• Could indigenous life colonize earth after a Venus sample return - the study came to the conclusion that due to the high acidity then these life forms if they exist are unlikely to be able to colonize Earth. But  Dirk Schulze-Makuch  was not convinced by this conclusion - so that suggests there is room for discussion here. I am not either.
• Acid environments on Earth - could the lifeforms, if acidophiles, colonize some of the most acidic environments on Earth?
• Retained capabilities - also - microbes often retain capabilities that they no longer need. Even though it would be billions of years since these microbes lived in Earth like environments,could some might retain capabilities from those times to live in less acidic environments than for the Venus clouds.
• Could there be micro habitats in the Venus clouds created by life? We haven't studied the clouds in detail close up, only from orbit, or with instruments with limited capabilities. Especially if there is life there, then we know that life can transform habitats and form micro-habitats. If that's so, there could be micro-habitats in the clouds caused by life processes that are not so acidic, inhabited by symbionts which would perhaps need the capability to live in non acidic environments. If so, then these habitats could be colonized by Earth life, and in the reverse direction, the life in those habitats could be pre-adapted to less acidic environments so more likely to be able to survive on Earth.
• Could gene transfer agents transfer capabilities? If Venus and Earth shared life late enough in the solar system, after the evolution of modern DNA life, you have the possibility of Gene Transfer Agents, those tiny virus like particles, well below optical resolution, able to transfer DNA from one micro-organism to another, very readily, as we've seen already, in that striking experiment where 47% of the culturable microbes in sea water had taken up antibiotic resistance from GTA's. after they were left overnight in bags filled with sea water and the GTA's.
  
  In this way, Venusian cells even unable to survive on Earth; even if they are dead, might be able to transfer some of their genetic material to Earth archaea - so transforming them and adding new capabilities. This is also a potential issue for forward contamination of Venus clouds as well. Earth archaea could transfer genetic material to microbes in the clouds in the same way even if they can't survive there themselves.

Does it matter if life from the Venus clouds gets established on Earth

You might wonder, okay we are required by the Outer Space Treaty to protect Earth from harmful contamination from Venus. But does it really matter if life from Venus gets established on Earth, or genetic material gets transferred to Earth archaea via GTA's.? Would it indeed be harmful if this happens? If we can show that it is not harmful, there is no cause for concern, and also, we don't need to worry about the OST either (as the clause refers to "harmful contamination").

So, just to go over it quickly, some of the things that could happen are similar to those for Mars.

• Pathogen of humans or our crops or animals, sea creatures, plants, trees. Doesn't need to be adapted to us. A disease of microbes for instance can directly infect humans without any adaptations, as happens with Legionnaire's disease, a disease of amoeba that happens to be able to reproduce also in human lungs. Indeed pathogens most usually adapt to keep their host alive for longer, not to kill their host.
• Is able to live on our skin (e.g. fungal infection), in our lungs, in our sinuses, or perhaps in our stomachs. That last possibility is an obvious microhabitat for an acidophile from Venus - though it would be used to sulfuric acid rather than hydrochloric acid of gastric acid (the Venus atmosphere does have HCl as well however).
  
    Perhaps just possibly, it would be able to reproduce in the stomachs of animals, and ourselves, and interfere with digestion, or create byproducts poisonous to us or the animal?
• Takes the place of some other organism in an ecosystem but behaves differently so disrupting natural cycles
• Is an allergen or creates allergens as a byproduct
• Creates a poisonous byproduct that interferes with human or other animal biological processes. For a simple example, green algae produce a chemical that it's thought, may cause Alzheimer's disease in humans. The way it works is interesting also, it creates a non protein amino acid, β-N-methylamino-l-alanine (BMAA), which substitutes for the protein amino acid, L-serine, and this leads to cells to cluster together and die. A microbe from another planet might well create chemicals that resemble ones in our body but are not identical and get substituted for them, and so disrupt the way our cells work or the way cells of other organisms work. 
  
  It is of no benefit at all to the green algae to cause Alzheimer's and is not part of its natural cycle. It doesn't even colonize humans. Just creates a chemical which gets concentrated in shellfish and the like, and may possibly (not totally confirmed yet), when eaten by humans, cause Alzheimer's

Life returned to Earth from another planet may well be harmless, but there are many ways that it could cause harm, also. We can't know with reasonable certainty until we know something about the form of life and how it works.

XNA based life in the Venus clouds

Finally, there is the possibility that Venusian life is not based on DNA but some other basis such as XNA (change of backbone) or something more radical than that. If so then we can't really generalize from DNA to capabilities of XNA.

Rotating DNA animation. Could life on Venus have a different backbone from DNA , using PNA, HNA, TNA, GNA or other XNA?

Here XNA is a general term for nucleic acid analogues - with the same bases as DNA but a different "backbone", in place of the Deoxyribose of DNA. These include HNA, PNA, TNA or GNA (Hextose, Peptide, Therose or Glycol NA). The PNA world hypothesis for instance suggests that life on Earth went through an earlier stage where it used PNA (peptide nucleic "acid") before it started to use RNA or DNA. That's because DNA and RNA are so complex it is a little hard to see how they arose from non living chemicals alone.

Life on Venus could have done the same, but maybe didn't end up as DNA, may still uses PNA or evolved to some different form of XNA.

That raises the possibility that XNA based life could be better at coping with Earth conditions than DNA itself. This could be possible, if it is really a completely different form of life with different metabolism, cell machinery, etc. and has never had any previous contact with the Earth environment. If there does turn out to be life in the Venus clouds, then, the situation is not that different from the situation for Mars.

Venus cloud life might give the best chance for XNA in our solar system

The Venusian clouds indeed might give us one of our best chances of finding XNA in our solar system - in the remote case where there is life there. That's because for billions of years it has been almost impossible for Earth life to be transferred to Venus. The surface of Venus is so hot that Earth life would be destroyed soon after it got there, if it made it all the way to the surface of Venus.

The other way around also, then it is almost impossible for the cloud top life of Venus, if it exists, to be ejected through the thick atmosphere as the result of meteorite impacts on the surface of Venus, with enough velocity to leave the strong Venus gravity and get transferred to Earth or Mars. A huge asteroid impact on Venus would disturb the cloud deck for sure, but could even a giant impact send significant amounts of the high Venusian atmosphere into space? 

Chandra has put forward a controversial theory that the solar wind could transfer microbes from the upper Venus atmosphere (high above the cloud decks) to Earth at times when the planets are aligned. See Microbes Could Travel from Venus to Earth However other scientists find his research unconvincing, so far, with many details to be filled in. For instance, it doesn't seem that the solar wind would have enough energy to remove a microbe from the Venus gravity well, since it is far heavier than the ions it can transport. Also, any dormant microbes that did get ejected from Venus would also be vulnerable to cosmic radiation and high levels of UV, which they might not be adapted to.

So, it seems at least possible that life could have evolved independently on Venus, and has been there ever since. If so, it would probably be a form of XNA. In that case all bets are off as far as planetary protection of the Earth. We can't say much by analogy with DNA life even about its size, or its properties or its adaptability to different environments/.There are other places that could have XNA, including Mars, or comets. But Venus has been more isolated from Earth than any of those. Even the Europan oceans could potentially share DNA with Earth through impacts on Earth sending debris all the way to Europa. This probably was only be possible for Venus in the very early solar system. The Venusian surface might also have been too hostile for Earth life already by the time Earth was habitable.

Hazards of XNA from Venus

If it turns out that Venusian life is based on XNA, this does not make it safe for Earth life. Yes, as some say, the XNA would not be adapted to Earth life. But the other way around, Earth life might not recognize XNA as potentially harmful (as in the Lederberg quote above). And adaptations of microbes are usually in the direction of keeping the host alive for longer; it is of no benefit to a microbe that infects a human for the human to die. It might also be able to out compete Earth microbes in their own habitats, and yet behave differently from them, transforming ecosystems. It could damage crops or animals, or change the balance in the seas. In the worst case, XNA based life might prove to be better than DNA based life all round. For instance it might be more efficient at metabolizing and reproducing. The very worst case is goodbye DNA. For these and other reasons, then researchers in the field of synthetic biology, who are actually contemplating the possibility of creating new life based on XNA instead of DNA (by substituting XNA for DNA in a cell, complex process but most of it is now worked out) - they are exceedingly cautious about the research.

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 forms). 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."

So, the idea is that the experiments need to be designed so that there is less than a 1 in 10²⁰ chance of the XNA reproducing in the wild outside the laboratory (most likely by making it dependent on some substance not available "in the wild" outside of the laboratory).

Impossibility of containing XNA at sufficient probability levels

XNA returned from Venus could not be contained at those sort of probability levels. It would more likely be a one in a million type containment such as is suggested for the Mars sample return proposals. One in a million containment is already potentially a major engineering challenge if the particles to be contained are small, such as 0.01 microns across in the case of the Mars sample receiving laboratory. (Incidentally, my own view, I also think the plans for one in a million level containment of a Mars sample are totally inadequate levels of probability for Mars, if the sample happens to contain XNA or substantially different life forms). For the issues for a Mars sample return see Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisited and  Need For Caution For An Early Mars Sample Return - Opinion Piece

COSPAR study of the Venus atmosphere didn't consider XNA or gene transfer agents

Here the situation is similar to the studies of risk for Mars sample return. Often new planetary protection studies bring up the possibility of new risks not considered in previous studies. The 2009 Mars sample return study by the US National Research Council brought up the new possibility that Mars life forms might be smaller than previously thought and added a new recommendation to contain ultramicrobacteria at 0.2 microns across. The 2012 Mars sample return study by the European Space Foundation added another new recommendation, this time to contain Gene Transfer Agents only 0.01 microns across if possible - it was published just after the discovery of easy transmission of GTA's. between unrelated species of microbes in sea water.

Both studies of Mars sample return mention XNA but they do not go into it in any depth, particularly, they don't mention the researches into safety considerations for XNA in Earth laboratories. Also neither study considered the possibility that the life forms to be contained are smaller than the smallest known Earth microbes. This seems at least possible since, though 0.2 microns seems to be the smallest organism that could contain all the cell machinery of modern life, early cells on Earth must have been smaller than the ultramicrobacteria of the order of tens of nanometers across. Also, we have no way to be sure of the size of XNA lifeforms.

The Venus planetary protection study didn't consider GTA's. or XNA, and doubts were raised about their conclusions about the possibility of Earth originated acidophiles to survive in the Venus atmosphere. Also the study was not based on experimentation and we have limited knowledge of the Venus upper atmosphere. We don't know enough yet to make an accurate simulation of it in a laboratory on Earth for testing. The clouds may well turn out to be so utterly hostile to Earth life that there is no chance it could survive there. It may well have no Venusian life in it either. But I'm not sure we can conclude this for certain yet. I think it is possible that a new study, taking account of these ideas, would change the provisional classification of the Venus atmosphere for both forward and backward contamination.

Need to study in situ first

For all these reasons, putting my own personal view here for discussion, I think the wisest approach in the case of the Venusian clouds is to study them "in situ" to start with. Perhaps we shouldn't bring unsterilized samples back to Earth quite yet.

We may get this in situ search soon. Some scientists working on designs for the next Russian mission to Venus, Venera D which hopefully will launch some time in the 2020s. Provisionally 2026. The original plan was for a balloon (as well as a lander and orbiter). They want to include ideas from the Northrup group VAMP project for an unmanned aerial vehicle for Venus. This would actually deploy outside of the Venus atmosphere and do a hypersonic entry. Because it is so large and light, it decelerates very high in the Venus atmosphere, and so does not need an aeroshell as it decelerates more slowly and the skin is not raised to a high temperature

.

It inflates before it enters the atmosphere (see Patent). Because it is so low in density (low ballistic coefficient), it decelerats slowly in the very thin upper atmosphere, so generating much less heat. So it doesn't need an aeroshell, though, its outer envelope is reinforced to withstand up to 1200 C along leading edges

They hope it can be used for Venus, and also Titan, possibly Mars.

Eventually we can send humans to the clouds. The HAVOC idea is to do this. Their airship expands after it enters the Venus atmosphere, but the rest of the design is very similar. This is a video showing how it would work.

Need to treat the Venus atmosphere as a category III destination for COSPAR

Apart from classification issues, I feel personally that we should sterilize spacecraft and instruments designed to study the cloud tops of Venus, until we know a bit more about it, as the classification is not certain enough that it might not change in light of future discoveries.

Okay this may add 10% to the cost of the mission (sterilizing Viking added an estimated 10% to the mission cost). That is a big increase when margins are tight, I understand. But that is well worth it to be totally sure that e.g. if you do detect apparent signs of life in the clouds, such as DNA or amino acids, that it comes from Venus and not your spaceship. Also to make sure you do not contaminate Venus samples or the clouds themselves with reproducing life, including the probably remote chances of some archaea with pH 0 acidophile capabilities getting transferred to Venus on our spacecraft, or some of the archaea able to share their DNA with Venusian organisms via GTA's., or Venusian XNA able to out-compete DNA. If we go into this with our eyes open, and debate all the possibilities, however extreme, we will be able to explore the solar system safely.

I think also that we shouldn't think about sending humans there until we've studied it a bit in situ to see if there is life there, remote though the possibility probably is. This should be regarded as an exciting possibility. In my own view again, then if there is life in the Venus clouds, especially interestingly different, or XNA based life, this is such a wonderful and interesting result for biology and science and evolution - and in the long run for humanity generally - that it far outweighs the disappointment that we need to postpone colonization of the cloud colonies for a later date

We should celebrate the discovery of other forms of life anywhere in the solar system. Also, if discovered, proper study of exoplanet life should take priority over colonization, in my view, if there are any conflicts of interest. What do you think?

Venus may eventually be one of the best places to send humans to in the solar system, at least in terms of habitability. You can argue a surprisingly good case for it. See also: Will we Build Colonies that Float Over Venus like Buckminster Fuller's "Cloud Nine"? But I'd say, let's explore it with sterile robots first, if there is any chance of finding life in the atmosphere, even if we think the chance seems rather remote.

Objective for humans to Mars

If we decide we shouldn't send humans to the Mars surface quite yet, there are many exciting missions we can do to the Mars system. You can explore Mars by telepresence from orbit, or from its moons Phobos and Deimos.

Telerobotics as a fast way for humans to explore Mars from orbit

Telerobotics lets us explore Mars much more quickly with humans in the loop. And you'd use an exciting and spectacular orbit for early stages of telerobotic exploration of Mars, following the HERRO plans. It comes in close to the poles of Mars, swings around over the sunny side in the equatorial regions and then out again close to the other pole, until Mars dwindles again into a small distant planet - and does this twice every day.

Imagine the view! From space Mars looks quite home-like, and the telerobotics will let you experience the Martian surface more directly than you could with spacecraft, actually touch and see things on the surface without the spacesuit in your way and with enhanced vision, blue sky also if you like. It's like being in the ISS, but orbiting another planet.

12th April 2011: International Space Station astronaut Cady Coleman takes pictures of the Earth from inside the cupola viewing window.- I've "photoshopped" in Hubble's photograph of Mars from 2003 to give an impression of the view of an astronaut exploring Mars from orbit.

This is a video I did which simulates the orbit they would use - in orbiter. I use a futuristic spacecraft as that was the easiest way to do it. Apart from that, it is the same as the orbit suggested for HERRO.

It would be a spectacular orbit and a tremendously humanly interesting and exciting mission to explore Mars this way. The study for HERRO found that a single mission to explore Mars by telepresence from orbit would achieve more science return than three missions by the same number of crew to the surface - which of course would cost vastly more. Here is a powerpoint presentation from the HERRO team, with details of the comparison.

Then, you'd also have broadband streaming from Mars. As well as being very safe, also comfortable for the crew, you'd also have wide-field 3D binocular vision. It's amazing what a difference this makes, I recently tried out the HT Vive 3D recreation of Apollo 11. We'd have similar 3D virtual reality experience of the Mars surface. Also, it would actually be a much clearer vision than you'd have from the surface in spacesuits, digitally enhanced to make it easier to distinguish colours (without white balancing the Mars surface is an almost uniform reddish grayish brown to human eyes)|.

Here is this hololens vision again, which though it's not telepresence, I think gives a good idea of what it might be like for those operating rovers on Mars in real time from orbit, some time in the future with this vision.

It's safer too. No need to suit up. No risk from solar storms - at worst you have to go to a storm shelter in your spaceship, not rush back to your habitat as fast as you can to get out of the storm in time. No risk of falling over and damaging your spacesuit. And when you need to take a break, have your lunch, or whatever, you can just take it up again where you left off, indeed leave the robot doing some task while you have your lunch or sleep.

This is an artist's impression from ESA showing a telerobotically operated rover on Mars

The ESA are currently testing rovers controlled from orbit - which will eventually use binocular vision and haptic feedback. in a program called IMPACT. This is their artist's rendering of such a rover on Mars.Tim Peake's recent test of controlling another rover on Earth from the ISS was part of this program. Previously, Andreas Morgeson drove the rover shown in this rendering, on Earth from the ISS, using binocular vision and haptic feedback to remove and plug a pin into a small hole with a tolerance of 0.15 mm, less than a sixth of a millimeter. He did this successfully, video of the actual event here.

Telerobotic drilling versus human drilling

Drilling is especially important for the search for past life, as well as any present day life that may live deep underground in geological hot spots, or kilometers below the surface, or beneath ice sheets. However, in Mars conditions, robots can drill as easily as humans in spacesuits, and probably more so. The Apollo astronauts had a lot of trouble drilling by hand by just two meters, sometimes falling over. So humans have problems too.

If you want a deeper hole, you can't use water as a lubricant on Mars, so you can't use a conventional drilling rig. The best technology is likely to be the robotic self hammering mole, has potential to drill much deeper than either of those, and certainly to the ten meters depth needed to find organics not degraded by cosmic radiation and solar storms. These moles may eventually drill for tens and hundreds of meters, even for kilometers in Mars conditions at ten to twenty meters a day.

These moles don't need an astronaut to operate them. ExoMars will be able to drill down two meters, using a different approach. The Insight lander was going to drill three to five meters using a robotic mole. The regolith thickness varies, here is an estimate for the site of the Insight lander - they estimate that ~90% of the Insight landing region is covered by a regolith that is at least ~2 to 3 m thick. ... and that the regolith is 5 to 6 m thick over ~50% of the region. Honeybee robotic are working on a drill that will be able to drill through gypsum and hard ice to a depth of hundreds of meters. They say that their inchworm mole will be capable of drilling up to tens of kilometers through soil, ice and rock without need for a tether and then return to the surface.

Drilling is very slow at present - it takes a week on Curiosity. However that is with a huge amount of latency. The team send commands to Curiosity typically the next day after they get the images back. Also it's not really fair to compare that one week with the time it takes to actually drill out a sample on Earth because it also includes the time needed to take it back to the laboratory and analyse it, which is done in situ on Mars. So it's not as bad as it might seem, but it could be done a lot faster via telerobotics. For more on this see this presentation by Marc Boucher (slides and audio).

Mobility for humans and robots

Our rovers travel very slowly on Mars but that's mainly because of the turn around time of 24 hours between getting the images and sending the next day's instructions, and limited autonomy. The Apollo lunar roving vehicle had a rated top speed of 8 km / hour (though it could go faster), weighed 210 kg, for the entire vehicle, and had a range of 92 km, nearly twice the total distance Opportunity covered in ten years. So it's not lack of power that limits our rovers - they could go much faster, and further, if there was the need to design them to do so.

We can use the same methods to power robots on the surface as you can use for human driven rovers. So, for instance, we can use Zubrin's ideas to generate fuel in situ using hydrogen feedstock from Earth. Or we can use solar power and batteries, adapting the Mars One idea to spread a large area of thin film solar photovoltaics over the Mars surface for power. Perhaps we could use batteries with enough charge to last for a few hours at 8 km / hour, as for the lunar rover, and then when the charge runs out, then it leaves the battery to charge up, and uses power direct from its own solar panels until it is ready to do another tens of kilometers long journey again.

In this way, the methods designed for human missions to the surface can be used for our robots also, so that they can travel faster, and explore more in each day. The robots don't have to go back to a base, are not limited by the amount of oxygen and food they can take with them, can travel right up to habitable regions if sufficiently sterilized. Humans can start telerobotic control within seconds, in a shirt sleeve environment, "teleport" from one rover to another from orbit. And of course when not controlled by humans in orbit, they can be controlled by teams of scientists on Earth as before. So it's not at all clear even that the robots are less mobile than humans. Once the technology is well developed they might even be more mobile.

Imagining a telepresence mission in the HERRO molniya type orbit

Imagine yourself in orbit around Mars - in a Molniya orbit - comes round to the sunny side of Mars twice a Martian day - you go really close to the surface - and spend some time there controlling rovers on the surface - driving them around - with reality headsets like the Occulus Rift -

- the Mars astronauts in orbit could explore the surface with headsets like this - and haptic feedback gloves so you can feel what you are doing, and omni directional treadmills like the virtuix omni

and automatically enhanced vision with everything you see on Mars streamed back to Earth so everyone back here can join in and see what you see exactly as you see it whenever you explore the surface of Mars.
Then after a few hours of that you see that Mars is now getting further away, becomes smaller, and then 12 hours later you come in again for another close approach and real time exploring - you can continue to explore all the time - but when you are really close you can control things on the surface in real time as if you were there.

Small planes and entomopters etc

You could fly planes around on Mars, small planes, or entomopters - same design as a bumble bee. Lightweight, you could carry many of these along with the humans in a human mission to Mars orbit or the Mars moons to send on to the Mars surface.

Many other ideas like that - surely much more fun, to operate those from orbit around Mars, in a shirt sleeves environment than living a troglodyte existence on the surface under meters thick layers of soil, going out only rarely to keep down your lifetime radiation dosage - and knowing all the time that just by being there you have contaminated Mars and made it far harder for scientists to find out interesting things about biology and alternative forms of biology and the early history of evolution.

Also all this would be great for collaboration - probably need a big international expedition to send the humans out to orbit around Mars. But as well as that, anyone who can send a spacecraft to Mars (probably many countries by then) can send landers, for them to operate telerobotically. The more the better really. So it is something that all countries with interest in space could work on together, each contributing different things depending on their expertise.

Safe ways to get humans to Mars orbit or its moons to avoid any risk of crashes on the surface

You couldn't do aerocapture in the Mars atmosphere as a way to get into orbit. It would be far too risky. Also Hohmann transfer with insertion burns are too risky also, as the insertion burn is done as close to Mars as possible to reduce the amount of fuel needed due to the Oberth effect. So you would need to be very sure that the insertion burn can't go on too long and end up on an impact trajectory with Mars.

I suggest ballistic capture is a far better method for human missions to Mars. The idea is that you launch the spacecraft to arrive ahead of Mars at just the right point for it to capture you as a temporary satellite. Once you leave Earth, you are already on a trajectory that ends up with your spaceship getting captured temporarily in a distant Mars orbit when it gets there, with no need for an insertion burn. Then once you are in that orbit, you use ion thrusters to spiral down to lower permanent orbits around Mars.

This is surely the safest of all the ways proposed to get into a Mars orbit, and the best way to prevent a crash of a human occupied spaceship on Mars.

Then you also have the flybys. Flybys are safe because although they involve precision targeting, you have months to set the target up. Also, the ones that are of most interest for Mars are free return, so even if your rocket fails, you are still on an orbit that will take you back to Earth again. You would use trajectory biasing of course, so that as you leave Earth you are biased away from Mars rather than towards it and use fine adjustment then to target the flyby orbit.

We have done many flybys, delicate ones, repeatedly for Saturn's moons with Cassini, and get them right every time, so it is obviously one thing we know how to do reliably. This has no time critical insertion burns. Just gentle thrusts nudging until you are in the right trajectory, which you set up long in advance of the actual flyby.

Interesting flyby and orbital missions for Mars

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. Advantages of this are

• Least delta v of all the proposals, so also the cheapest
• Astronauts are close enough to Mars for direct telepresence control for several hours for each fly by, still remain close for days after the first flyby and before the second fly by, and close enough to be a major asset over Earth based control for the entire year.
• It's a "free return" mission - you don't need to do any extra delta v to get back to Earth. The second flyby, an Earth year later, takes you back to Earth even if you don't do anything.

Robert Zubrin's plan has several advantages over Denis Tito's Inspiration Mars, which is the other free return mission proposal.

• You can do it more often, roughly every two years,
• It doesn't have the high speed return of Inspiration Mars so less issues with aerobraking into the Earth atmosphere on return
• You have far more time for near to Mars telerobotics - with Denis Tito's mission you just have the one, very fast flyby of Mars and then it is over.
• But is a longer mission by 200 days.

I'm not sure that the Inspiration Mars 500 days is such an advantage over 700 days. I think if we can manage 500 days safely (surely not for a while yet) - then we can probably do 700 days also. (it is an extremely poor safety margin for Inspiration Mars if most astronauts are close to death at the end of 500 days). Also the double Athena can be done every two years, doesn't need any special alignment with Venus, and it has a much slower return trajectory relative to Earth - can just do normal aerobraking much like the return from the Moon, which Inspiration Mars can't do because it has a far faster return velocity delta v relative to Earth. Anyway its great advantage is that you are close enough to Mars for hours during each fly by - and in between you spend days really close, close enough to do things like drive rovers in real time and supervise experiments.

The HERRO mission suggested a near sun synchronous Molniya orbit, which is elongated, similar to a Mars capture orbit. This is the easiest orbit to get to in terms of delta v, needing a similar amount of rocket fuel to a mission to the Moon for the same payload. This has the advantages that

• Less fuel to get there
• Approaches the sunny side of Mars twice a day, each time visiting the opposite hemisphere,
  
  So the entire surface of Mars is available for close up direct telepresence control of the landers, in full sunlight, every single day, by just the one crew.
  See:  HERRO mission to mars using telerobotic surface exploration from orbit

Turns out, if you choose just the right orbit, it's ideal for studying Mars by telepresence. You use a slowly precessing sun synchronous Molniya type half sol orbit. This is a precessing orbit that automatically keeps your spacecraft approaching Mars on the sunny side twice a day, all through the Martian year.

This shows how you get into this orbit - just directly from the Earth-Mars transfer orbit.

With this orbit, you have several hours of close up telepresence every 12 hours over opposite sides of Mars each time, also always on the sunny side of Mars. The delta v is the same, to all intents and purposes as a Mars surface using aerobraking. But without the dangerous descent to Mars and without the expense of developing human rated landing equipment -I think pretty clear it would cost less than a surface mission.

All of these missions have the disadvantage that you have to take all your shielding for the entire mission with you. You'd need "storm shelters" for solar storms also. This would be worked out with the lunar precursor missions to L2 etc - I don't think we should do a mission like this without experience of similar missions close to Earth. And any Mars mission needs to spend around a year combined (there and back) fully exposed to solar storms and the cosmic radiation anyway.

Its moons are actually, rather interesting places for a human to visit. In some ways they are more exciting than the surface, as we'll see, especially when combined with telerobotic exploration of Mars. Also, they are far easier places to land on safely and return. And there is almost no risk of introducing Earth life to Mars accidentally, so long as you get there without use of aerobraking. I think it may be some time myself before we can send humans even this far safely. There are many more challenges than there are for a lunar landing. The task of physically getting to Mars orbit is perhaps the least of many issues. But when we do get there, then these could be really exciting places to visit,

So which of the two moons should we visit? The most detailed proposal is by Lockheed Martin in their "Red Rocks project"  as part of their "Stepping Stones to Mars" program. And in their comparison study, Deimos beats Phobos on almost every score - though Phobos does have a couple of major advantages. 

Advantages of Deimos

So - the advantages of Deimos first

• It has a South pole almost permanently shadowed - amongst the coldest places in the inner solar system. This also is a place where you are completely sheltered from the dangerous radiation in solar flares (which emanate from the direction of the sun). And it has natural cooling for any rocket fuel that needs to be kept at cryogenic temperatures (it is also ideal for infra red observation).
• The permanently shadowed craters are probably a good place to study (just as for the Moon's craters of eternal night), with an ice record of the early solar system and materials from early Mars. It may also be a source of ice for colonists.
• Close to these places of permanent shadow, you have a site of continuous summer sunlight to place your solar panels.
• You also have permanent line of sight communication with Earth 24/7 for nearly all the year except when Mars is behind the sun.
• Deimos is almost synchronous with the surface of Mars - and tidally locked - so you can have continuous line of sight access of Mars for telerobotic communication.
• Any site on the surface of Mars is accessible for 60 hours at a time from Deimos. By comparison, from Phobos, any site is only accessible for four hours at a time.
• A typical site on Mars is visible from Deimos for 45% of the time, and 97.5% of Mars is directly accessible via telepresence at some point or another.
• The required delta v to get there is somewhat less than for Phobos.
• Surface materials can be used for resource utilization and to cover the habitat to protect from cosmic radiation.
• It's an interesting place to study in its own right.

Advantages of Phobos

There are two major advantages of Phobos,

• because it is closer to Mars, it has a two way time delay for telerobotic exploration of only 40 ms, while Deimos has a two way time delay of 134 ms.
• It has a crater, Stickney crater, on the Mars facing side. A party in Stickney crater would be protected from about 90% of cosmic and solar radiation, possibly more, at least according to this article (if they got it right). That's because it is protected by the crater walls, Phobos, and Mars itself which is overhead, and for solar storms it would be out of the direct line of the storms for most of the time. It is one of the places in the inner solar system most protected from cosmic radiation, even more so than the poles of the Moon. Only the lunar caves and Martian caves are more protected from cosmic radiation - or the high Venus cloud decks (and of course, Earth itself).

Stickney crater on Phobos. This large crater faces towards Mars. A base sited here would be protected from solar storms, and also from cosmic radiation. It's blocked by Mars overhead, Phobos below and the crater rim to all sides, and so gets only 10% of the cosmic radiation of an unprotected base. 

Phobos also probably has a high percentage of material from Mars in its regolith, and larger meteorites surely as well. So you can study the geology of Mars by looking at fragments of rocks on the surface of Phobos. Possibly the biology of Mars also.

Phobos was the target for the Planetary Society workshop in 2015. They base it around the SLS (Space Launch System). We send cargo to the Mars system in advance before any humans get there:

• Two spacecraft are waiting in Mars, with chemical propulsion. One to deliver the crew to Phobos and back, and the other, to return the crew to Earth.
• A habitat waiting for them on Phobos.

These are put in place using two SLS launches and then solar electric propulsion once in the Mars system. Solar electric propulsion is slow but it means they can deliver the cargo there outside of the normal launch windows to Mars (using ballistic transfer ideas).

Then two more SLS launches put all the equipment the human crew need for the journey to Mars into Earth orbit. Then crew then launch from Earth in a two and a half year mission which includes a 300 day stay on Phobos. When they get to Mars orbit they dock with the Phobos transfer stage which is already there and leave their deep space habitation module and dock with the Phobos habitat for their mission. They use the same transfer stage to get back again. Details on page 19 following of their report

Mining Phobos and Deimos

Deimos is also an asset for mining - it's not known for sure yet, but is similar in composition to meteorites that can have a large ice content. So it may have large deposits of water ice. If so that's of great value for fuel - and the delta v budget is such that it's actually one of the easier places to mine ice to return to LEO. As well as use in Mars orbit.

David Kuck in 1997 suggested starting up a Deimos Water Company to supply Earth orbit with water from Deimos. The Kuck mosquitoes are small unmanned craft that drill into Deimos and extract water from below the surface, use part of it as fuel to transport the rest back to Earth.

See also Mining Phobos and Deimos

This makes it a project that could be commercially viable, unlike Mars surface, through sale of ice to LEO.

Lack of gravity on the Martian moons

There is one major issue of course - the gravity, almost none. Can humans stay healthy with such low levels of gravity? Or - can we create artificial gravity on the surface (spinning habs)?

But perhaps this can be done with either a carousel type approach or with centrifugal sleeping quarters for the crew. I think this all depends on what turns out to be the requirement for artificial gravity to keep a human body healthy, and on what our tolerances are for spinning motions in AG environments - which we don't know anything about as yet. See also my sections in Case for Moon First:

• What about gravity - isn't that a big advantage for Mars over the Moon?
• Artificial gravity on the moon to augment lunar gravity

Free flying habitats

Artificial gravity is probably an easy matter to arrange in a free flying settlement in orbit. You can use a tether system to generate gravity for the earlier settlements. You can use materials from the Martian moons for shielding. Long term, you could use materials from the Martian moons eventually to build Stanford Torus type settlements in Mars orbit. Deimos has a mass of 1.48 * 10^12 metric tons, which at 15 metric tons per square meter is enough to make Stanford Tori with about 100,000 square kilometers of living area.

So, if you were to mine the whole of Deimos - not suggesting we do - but if we do - that's cosmic radiation shielding for roughly the size of Iceland, larger than Scotland, or Norway, more than twice the size of Switzerland, which could be useful for Mars orbital colonies. In terms of US states, that's about the size of Oregon or Colorado That's just the outermost hull which you can build on top of - and larger habitats might well have multiple "shells" within it - so that's a lower bound on the total land are you could create from Deimos using it for cosmic radiation shielding.

Anyway that's obviously for some way down the road, if we ever do that.

Planetary protection issues for Phobos and Deimos

When Russia proposed a sample return from Phobos, then it was classified as an"unrestricted category V" mission, meaning that no special precautions are needed. Despite that, Russia did plan to take some precautions on return of the sample, though not required for planetary protection according to the classification their mission received.

The Russian Fobos-Grunt spacecraft, which was designed to return a sample from Phobos to Earth. The spacecraft never got there, it failed to separate and fell back to Earth and was burnt up. This sample return mission got an "unrestricted category V" classification for planetary protection on the basis that Phobos couldn't be habitable for Earth life - but the Russians did plan to take some precautions even so.

There is no chance of present day life surviving on Phobos or Deimos to the best of our knowledge, no chance of habitability on the surface or below the surface. These moons are just too small to have any chance of liquid water even below the surface, so it's thought. But - there could be a very minute chance of dormant life, because Phobos receives material sent into orbit from Mars after meteorite impacts. Any life at least on the surface of Phobos would be sterilized over long time periods such as millions of years. But the most radioresistant life on Earth can resist the equivalent of four hundred thousand years of Mars surface cosmic radiation, although not evolved in the presence of ionizing radiation (as a byproduct of heat and desiccation resistance probably). For more on this: UV&Cosmic Radiation On Mars - Why They Aren't Lethal For The "Swimming Pools For Bacteria" Life on Mars, evolved in presence of cosmic radiation could conceivably resist that much and possibly more. And Stickney crater gets just a tenth of those levels of radiation, so dormant spores there there could survive ten times longer, and more so if somewhat buried.

So given that material is sent into orbit from Mars every one or two million years, with the last known impact large enough to send material as far as Earth a little over 700,000 years ago, there would seem to be a small chance of dormant life on Phobos - that is if life from Mars can be transferred on meteorites at all, which we don't know yet. But theoretically it would be possible. I think myself that this suggests it would be worth while doing robotic in situ exploration of Phobos and Deimos first before we send humans there. And if signs of life are found there, dormant life, to re-evaluate the situation and take appropriate precautions depending on what is found.

In the forward direction also - then though to best of our knowledge, there is no chance of life from Earth surviving on Phobos or Deimos, there could be regions there of especial interest for the study of organics in the early solar system and dormant life. For instance what if there are ice deposits at the South pole of Deimos - including samples of organics from early Mars itself? Then we would need to keep humans well away from these until we have a chance to study them in situ and work out what effect a human base would have on them.

Could a human occupied base there be kept so clean that there is minimal impact on the study of ancient organics in the ice surrounding the base? If not, what can we do? Deimos is rather tiny, only 12.4 km in diameter. After a year or two, then the entire region around the base would probably be covered in footprints unless you take special precautions to minimize the impact of humans on the Moon. And what about refuse piles, human wastes etc? If Deimos is interesting in its pristine state - well that's something we need to think through before we send humans there. Anyway, by then we probably have experience already of bases on the Moon so may be able to use that to assess what impact a human base has on the area immediately surrounding a human habitat.

More ideas for these early orbital or flyby missions

With of HERRO, and indeed for the other missions also, you could send supplies to Mars in advance in separate duplicate spaceships before the human mission gets there. Most of the cost of an innovative mission is in the design, so it often adds little to the costs, percentage wise, to make several duplicates of the spaceship.

So, you have a habitat there already, in orbit around Mars,and with all the systems functioning including life support. Preferably, have two such ships filled with extra supplies, before you send the first humans there.

They would be fully fueled lifeboat ships able to get the crew back to Earth, or for them to survive in if systems in the main ship fail. You can also use them as extra living space at Mars during the mission, and as long term assets in Mars orbit.

Since these lifeboat ships don't need crew or provisions for the journey out - they could be filled with extra supplies, fuel and spare parts instead. These supplies could then be transferred to the main ship and used as extra shielding for the stay at Mars. In the worst case you can cannibalize the other ships themselves, for repairs, or if the main ship fails, transfer the mission to another ship.

And - if we were looking forwards towards such an expedition - all rovers to the surface of Mars could be fitted with binocular vision and hands with haptic feedback by default. Anyone who sent a spacecraft to Mars would be sure to set it up so that it can be controlled easily by telepresence whenever there are astronauts in close orbit around Mars.

Suppose we had a lead time, say of a decade in the run up to the first human missions to Mars orbit (during which we have human missions to L2 etc). Then by the time humans get there, we'd have a decade worth of Mars rovers and landers, all equipped to be controlled via telepresence, ready for use when the first human missions get to Mars orbit.

Later orbital missions could mine Deimos for materials, using the likes of the Kuck mosquitoes - dedicated small spacecraft to shuttle materials back and forth from the moons to the settlements. If there is ice in Deimos; you could use this as rocket fuel to export this extra shielding to the habitat,

Artificial real time

But there is another thing we can do - and that's to do autonomous exploration from Earth, using "artificial real time" which lets you drive a rover around on Mars even with a huge time delay of minutes. At the moment the way we control our rovers on Mars is hugely time inefficient. We could as easily control rovers on Pluto, because they download the data for one day, and use that to direct the rover's operations for the next day.

There's no point in trying to speed that up though, because it is hard to get a data link from Mars to Earth. Once a day is about all we can manage easily, because our orbiters have their own work to do.

If we have a dedicated link though between Mars and Earth, satellites in orbit around Mars just to relay signals to Earth - our rovers could be hugely speeded up.

And - in a situation like that, we could also speed them up so much that using this idea of "artificial real time" from computer games, we could control them almost as easily as a rover on the Moon (say).

Telerobotics with humans in orbit compared to robots controlled from earth

That's not to say that humans to orbit controlling robots on the surface would be better than robots controlled from Earth, bearing in mind the costs of the two types of mission. I don't know if anyone has done a comparison study there.

You might be able to compensate for the advantage of humans in orbit by having many more robots on the surface for the same cost, especially if broadband communication is possible, better robotic autonomy, and techniques from gaming such as artificial real time (building up a copy of the Mars surface explored by your robot in your computer on Earth and navigating that to help speed up movement from a to b on Mars).

But a human expedition might well capture the public imagination and so permit a much faster exploration of Mars from orbit. And would be an exciting and fun expedition to follow, and interesting for the crew too.

As a later mission you could then go on to explore Phobos and Deimos. They have many advantages for exploration. For instance Phobos has meteorites and micrometeorites throughout its surface layer of regolith, from the entire history of Mars, back to when Phobos first formed or was captured. This probably includes meteorites from the time when Mars had global oceans and then later on, lakes. Our Mars meteorites on Earth all left Mars no more than twenty million years ago (because the terrestrial planets clear their orbits so NEOs have to be replenished over a twenty million year time period).

Deimos also has a Mars facing crater which helps protect it from cosmic radiation, and solar storms - Mars obscures it from the sun in its local daytime, except for a few hours a day. Deimos may well have ice too, as it is related to a type of asteroid that often does have ice in its constitution.

There are many other advantages and points of interest of Mars' two moons.

For more on this, see my: 

Exploring Mars By Telepresence From Orbit Or Phobos And Deimos

So, how soon can we do such a mission? I suggested that while we explore the Moon robotically, we work on closed systems research, and also artificial gravity in LEO. That makes sense for a Moon base which you plan to keep occupied for years on end. But what about a first flyby of Mars? When could we try that?

Need for new comparison studies of the various ways of exploring Mars

The HERRO comparison was just a small scale study, done several years ago. But I don't know of any other. It's surely high time that we had a much more thorough and detailed comparison study of the various possible ways of exploring Mars. We may get practical experience of telerobotics in space with lunar missions in the near future. When that happens I think we'll find that machines are far more capable than they were in the days of lunakhod, operated from Earth most of the time, semi-autonomous, route finding on their own, able to do many things just by themselves with occasional help from Earth.

In a situation like that - operated remotely from Earth, or semi-autonomous, doing a lot of their own driving from place to place and then the crew in orbit around Mars step in to control robots that need particular help. I think that it would be much more than a 3 to 1 ratio compared with them working directly on the surface in spacesuits. Also, 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.

Also, yes humans are great at "on the spot" decision making. But they are also able to make very rapid bad decisions, or uninformed decisions.

If the mission is a scientific one, then you need on the spot scientific expertise. To really take advantage of the low latency on Mars, you need astrobiologists in orbit or on the surface, and astrogeologists. They are the ones with the expertise that will let them make fast on the spot decisions. An astronaut without that expertise is still dependent, much like a rover, on instructions from their team of experts back on Earth. That's the same for both surface and telepresence missions from orbit. But the orbital missions do have the advantage that just through their nature they require everything the astronaut sees to be streamed back to Earth. So if the "on the spot" mission specialists miss something, it's not a big deal because some expert back on Earth will spot it instead. The orbital missions also are safer missions to send the astrobiologists and astrogeologists to, once we get to the point where we can send missions safely as far as Mars. You don't have to ask an expert in astrobiology to take the huge risks of a landing on Mars and exploring the surface with spacesuits. If the mission is extremely risky as a surface mission is likely to be, that then restricts it to those who are willing to take huge risks with their lives, such as test pilots and those who like taking part in risky activities. But if it is reasonably safe then you can send scientist who wish to spend a couple of years of their life on the mission.

I think a proper comparison study has to take all of this into account. Enthusiasts for one or the other approach are bound to be biased somewhat to what they consider to be the best method to explore Mars. So,. I think a proper comparison study is probably best done by neutral parties or best perhaps, a workshop / panel that includes proponents of both sides in the debate as well as neutral parties. The cost of such a panel or workshop would be peanuts compared to the costs of the missions that we might commit to in the future for the exploration of Mars.

Compared with Mars surface missions

First of all, whatever the cost, I don't think that COSPAR should pass a humans to the Mars surface mission for planetary protection reasons.

Artist's impression of a human astronaut on the Mars surface holding Oskar Pernefeldt's proposed International Flag of the Earth - the linked rings symbolize how the different parts of Earth are linked together. (This is the latest of several proposed "Flags of the Earth"). 

Before a mission like that could be approved, a COSPAR workshop would need to show that it is consistent with planetary protection requirements, and would not risk introducing Earth life to Mars surface habitats.

Either that or there would need to be international agreement that Mars no longer needs to be protected from Earth microbes. To my mind, seems unlikely that either could happen before the 2020s or 2030s. As for the idea of a compromise based on humans contaminating only part of Mars, I find it hard to see how that could be approved by COSPAR either. How could the experts in the COSPAR panels sign their name to a statement that they know could lead to Earth life being irreversibly introduced to Mars? I don't really get it, how that could happen.

Meanwhile we could use telerobots to plant flags on Mars if that is the main aim of the mission or to touch Mars. Or if humans touching somewhere else other than Earth and the Moon are considered vital to this mission, we can plant flags on Phobos or Deimos and touch those moons instead.

In more detail there - the Outer Space Treaty is the only treaty we have to prevent siting weapons of mass destruction in orbit, or nations laying military claim to the Moon, etc - it's the main reason that we are able to do peaceful co-operative exploration of space. As well as the outcry from space scientists, the international upheavals resulting from something like this would be enormous. There is no way that the US or NASA could do this.

So, it's the same for planetary protection provisions based on the Outer Space Treaty. They are like quarantine laws; it doesn't matter how you get into space, you are still bound by them as a citizen of your country, which in turn is a signatory of the OST. The US has agreed to make sure that any US citizen or anyone using US hardware will keep to the provisions of the Outer Space Treaty. and the same applies to any other signatory of the OST which includes just about all nations either space faring or with space faring ambitions. The United Arabic Emirates hasn't yet ratified the OST but they will still keep to the provisions.

Cost savings compared with surface missions

It's interesting to notice that these orbital missions would cost less than a surface mission. Especially HERRO and the double Athena which Robert Zubrin proposed as a lower cost precursor mission. In a comparison made for HERRO then the orbital mission does three times as much science for less cost. Here is a powerpoint presentation from the HERRO team, with details of the comparison. That's just one study, but it surely needs to be followed up with more detailed studies to check it. Also with the stimulus from 3D virtual reality computer games, the technology for telepresence has moved on hugely since then, so a new study would probably find it is even more of an advantage.

The reason the orbital missions can do so much more in the same time period compared with a surface mission is that

• You can control rovers anywhere on the surface of Mars, so can explore multiple sites at once.
• There is no need to suit up and travel to the area of interest, you can do it all with shirt sleeves environment within the spacecraft.
• When you take account of the reduced mobility of a human in a spacesuit, with clumsy pressurized gloves, then there's no great advantage of humans over telerobotically controlled rovers on the surface as far as mobility is concerned. Spacesuit technology of course will advance, but so also does telerobotic technology.

Then as well as that, there is no need at all to develop technology to land a human mission on the surface of Mars. That's not just a matter of delta v. You can land on Phobos or Deimos with a gentle use of delta v over a long period of time, and right up to the last minute, as for the Moon, if anything is wrong with your trajectory, you just abort and move away from the moon a bit, figure out what went wrong and try again, with hardly any waste of delta v due to the low gravity of these moons.

With a landing on Mars surface, everything has to go exactly right during the "eight minutes of terror" of the Curiosity landing. There's also almost no chance of humans intervening to save the mission if something goes wrong, as everything happens so quickly.

So - that's a whole new technology needed for a Mars surface landing that isn't needed at all for a Mars moon landing. And major human safety issues with a Mars surface landing that again are not issues at all for a Mars moon landing. You can study the Mars surface in a Molniya style Mars capture orbit, which requires less delta v than a surface mission. 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.

Telepresence would be immersive, not using primitive mouse and keyboard control, and need to be compared to humans in a pressurized spacesuit

First the robots controlled by humans would have some autonomy of course our rovers already have. For instance they may be able to drive autonomously or avoid collisions. On the spot decisions would be done by the humans. I don't think it is at all established that humans would have a significant advantage in a spacesuit over telepresence. It depends how you do the telepresence. Also, it's hard to simulate spacesuits on Earth - they need to be pressurized to the extent that the gloves are stiff and it requires significant effort to close your hands or move your fingers, for instance. Described as like wearing a garden hose over your fingers.

Also, if you navigate by using mouse clicks and keyboard presses and a computer screen it is very different from doing it with binocular vision, an omnidirectional treadmill, and haptic feedback. There are many more programmers working on computer games than on space systems and I think a way forward here will probably involve a fair bit of use of software developed for computer games. We've had several experiments in telepresence from orbit operating robots on the ground and each one is more advanced than the previous one - most recent one was a rover controlled from orbit by Tim Peake. But if we had all out effort to get this working then we could do much better.

The habitats themselves are almost the same in space or on the surface. The Mars atmosphere is not enough to make a difference. We have no idea what the effect is of Mars gravity - you can't just draw a line between zero g and full g. It could even be worse than zero g or better than full g and you can't join them with a straight line based on two data points. But even if Mars gravity is better for human health than full g, not impossible, we could generate it in orbit using artificial gravity. Yes you could have mobile habitats on the surface in a pressurized rover, but that is just adding to the complexity and remember those habitats still can't go anywhere near spots on Mars that are potentially habitable, again the question is, why all that extra difficulty, danger and expense to get those habitats to the surface when they could be in orbit, if the actual search for life has to be done remotely to avoid contaminating the habitats they search for and study?.

Summary of advantages of telerobotic exploration

Of course this needs a proper comparison study but there are many advantages to consider

• Best solution for planetary protection. It is hard to see how you could send humans to the surface of Mars without a risk of a hard landing which would contaminate a random area of Mars with all the hundreds of trillions of microbes in tens of thousands of species that accompany humans. If you introduce Earth life to Mars there is a major risk that you will detect life on Mars only to find that you brought it there yourself.
• Costs far less for more science return - one mission does as much as three to the surface, no need to develop the technology for humans to get to surface, or return from surface to orbit, no need to design for the Mars dust, and to keep the perchlorates out of the habitat.
• Safer . The landing on Mars is the most risky landing almost anywhere in the inner solar system.
• Crew don't endanger their lives in spacesuit EVA's. Crew at all times remain in shirt sleeves environment in the orbiting spacecraft. All they can endanger is the "avatar" rover they control on the surface. And that, if damaged, can be repaired potentially. While if e.g. you damage your air supply to a spacesuit you die.
• A rover can spend days, weeks, even months just at one spot on Mars using only electricity from sunlight while a human explorer has to return to base for provisions, oxygen etc frequently. For safety reasons a human astronaut would need to be close enough to a habitat or pressurized rover at any time to get back there on foot before their oxygen runs out. Even then they risk dying as a result of a sprained ankle or similar impairing their mobility.
• A rover doesn't have to put on a spacesuit every day, which takes up an hour or two of every day.
• Easily given capabilities beyond any human - easily given enhanced vision, can be made any desired size, can be given super-human powers such as great strength or dexterity or the ability to fly in the thin Mars atmosphere, because they can be made far lighter than humans.
• On the surface crew are exposed to the Mars dust, and perchlorates - they can use the suitport to keep them out of the habitat but this is another thing you have to design for which you don't need to think about in space
• Surface habitat and equipment has to be designed to cope with huge fluctuations of temperature. The Mars surface at night also often gets so cold that the carbon dioxide freezes out at night as frosts even for 100 days of the year in equatorial regions and the habitat has to cope with huge fluctuations of external temperature between day and night.
• Solar power is reliable in space - on the surface then every two years there's a possibility of Mars dust storms blocking out the sun, turning night to day
• Crew can explore several parts of Mars simultaneously, and "teleport" instantly from one experiment to another - leave one rover doing routine analysis while they drive another, or direct sampling for another - so the crew do all the interesting stuff and the rovers do all the dull stuff by themselves.
• Mars from orbit looks quite Earth like, an interesting planet and the elongated HERRO Molniya orbit is especially stunning with close flybys of the spectacular landscape and the polar caps every twelve hours, with the landscape skimming past below your spaceship followed by a long fly out so far that Mars becomes quite small. Every day you have that experience, twice, and each time coming in over a slightly different part of Mars. On the surface you'd be stuck in a single spot from then on and probably not see that much, and in the dust storms, nothing at all.
• When you drive the rovers on the surface with telepresence and haptic feedback, and virtual reality goggles to see the Mars landscape in 3D - you'd experience the surface vividly, far more so than if you were really there. Our eyes are not adapted to the Mars light and everything would seem dim and reddish brown, with colours hard to discern and a dull butterscotch sky. Exploring via avatars we can colour adjust automatically to resemble Earth lighting conditions, indeed with a blue sky if you like.
• Whatever you see is digital streamed (haptic feedback also), can be recorded and streamed back to Earth. Anyone on Earth can experience it as you did, and examine the images to see if we spot anything you missed.
• If anything goes wrong on the surface, you have everything recorded and streamed, so we can figure out what happened. There is no possibility of an accident where someone falls and dies and nobody is sure why it happened.

The main thing they lack is dexterity but this is rapidly improving with advancing technology. They are used for telerobotic surgery and deep drilling and many applications. You couldn't do surgery while wearing a spacesuit which I think helps highlight how telepresence could give you more precision of control and accuracy than hands on study of Mars in a spacesuit.

NASA organized a recent telerobotics symposium in 2012 and the conclusion of the conference was that telerobotics has great potential value for Mars exploration. The conference recommended their use during early orbital missions to Mars by humans, saying that a great opportunity would be missed if telerobotics was not used. But - why not just use telerobots from now on until we are sure of what we want to do on Mars?

Artist's impression of telerobotic exploration of Mars for the 2012 Exploration Telerobotics Symposium

Humans on the surface could start a new geological era on Mars - if they introduce Earth life irreversibly.

The eras so far, as we saw, are the earliest Noachian period of high meteorite bombardment and seas, the Hesperian period of volcanic activity and huge floods, the Amazonian period, as it is now, dry with some liquid water, a bit volcanic activity and occasional floods. On Earth geological epochs are named according to the prominent biology on the planet. So why not on Mars?

So, if we introduce Earth life irreversibly to Mars, we'd need a new name, maybe call it the Anthropocene again, as on Earth - of a Mars with Earth life on it, introduced by humans.

From then on for all future time, our civilization and all future civilizations on Earth would never have the opportunity to study the Amazonian period, with whatever unique lifeforms it might have. As we've seen in this book, it is well possible that Earth life could make Amazonian period Mars life extinct. After all, according to most theories of the origins of life, DNA life made its precursors on Earth, whatever they were, extinct. And later forms of DNA life made many earlier forms extinct. So it's certainly possible for one form of life to make another extinct over an entire planet.

Idea that we should exploit the small precious opportunity before humans land on Mars but shouldn't delay human landings

NASA's planetary protection office say that their job is to work out if the planet can be protected in the case of a successful human landing. So, they don't consider crashes of human occupied ships in their assessments. That is for NASA to look at, at a later stage. In their list of knowledge gaps for human extraterrestrial missions, they cover such things as leaks of microbes from spacesuits in EVA, and transport of microbes in the dust storms. But there is no mention at all of the effects of a crash of a human occupied spaceship anywhere in the list. They have to assume a 100% success rate for humans landing on Mars as without that assumption they would not be able to recommend any measures that could protect Mars from Earth life, even temporarily. Also, they no longer aim for biologically reversible exploration of Mars in the case of a human landing.

Their approach is that we will have a small precious window to find out as much as we can about Mars before humans introduce Earth life there by landing on the surface. Emily Lakdawalla, planetary geologist who often reports for the Planetary Society, expresses a similar sentiment in this article

"NASA recognizes that the potential for contamination is a problem, so there is a Planetary Protection Office that is specifically charged with overseeing how missions avoid contaminating Mars with Earth biota. There are two main approaches. One approach is to sterilize the heck out of anything that will actually be touching Mars. That's why Curiosity's wheels were specially wrapped throughout its final assembly, and why it was such a scandal that the drill bits were handled after sterilization. The other approach is to avoid landing in any location where you might encounter -- or accidentally create, should you crash -- a present-day habitable environment where Earth microbes could thrive. For instance, current rules prohibit NASA from targeting a mission containing a hot radioisotope thermoelectric generator (such as Mars 2020) anywhere near a place where a failed landing might place that generator close enough to subsurface ice that the heat of the decaying plutonium could melt it.

"But all bets are off once you send humans to Mars. There is absolutely no way to make a human clean of microbes. We are filthy with microbes, thousands and thousands of different species. We continuously shed them through every pore, every orifice, with every exhalation, and from every surface. True, almost all of our microscopic friends would fail to thrive in the radiation-baked, intensely cold and arid Martian environment. But life is incredibly tenacious. Sooner or later, humans will get to Mars; even if they die in the attempt, some of their microbial passengers will survive even the worst crash. Once we've put humans on the surface, alive or dead, it becomes much, much harder to identify native Martian life.

"This is one of many reasons I'm glad that The Planetary Society is advocating an orbit-first approach to human exploration. If we keep our filthy meatbag bodies in space and tele-operate sterile robots on the surface, we'll avoid irreversible contamination of Mars -- and obfuscation of the answer to the question of whether we're alone in the solar system -- for a little while longer. Maybe just long enough for robots to taste Martian water or discover Martian life."

The Planetary Society organized a workshop Humans Orbiting Mars in 2015 to explore the idea of exploring Mars from orbit first. Their report proposes a stepping stones approach to Mars, with missions to the Moon and asteroids, followed by missions to the moons of Mars and then boots on Mars towards the end of the 2030s.

Stepping stones approach proposed by the Planetary Society. See page 18 of their summary. Lockheed Martin proposed a similar approach previously.

Cassie Conley, NASA's planetary protection officer was David Livingston's guest on the SpaceShow in March 2016, and gave a very interesting talk about planetary protection. I posted some questions to her via email, so you can listen to her answers to them and get NASA's perspective on these issues in more detail. You can listen to her talk here.

Cassie Conley has also said she thinks Elon Musks' ideas have planetary protection issues, in an interview just before his big announcement here: Cassie Conley. Going to Mars Could Mess Up the Hunt for Alien Life There are no detailed guidelines yet for humans to Mars. These would be made by the international COSPAR committee which meets every two years, and all of their discussions to date have ended without any firm recommendations, saying that more information is needed.

Prestige or dishonour, first footsteps on Mars

Yes it would be an exciting day when the first human steps on the surface of Mars, and a matter of prestige for those concerned. This is something I have read about since a child, and would be as excited as anyone. But it might quickly change to dishonour if it is found that they introduced reproducing Earth micro-organisms to Mars. They might enter the history books as the people who contaminated Mars irreversibly. Why not let those first steps be taken by a telerobot instead, operated by a human in orbit around Mars?

Inspiration value of telerobots on Mars

Advocates for Mars surface colonization often talk about the inspiration of a human surface mission. But we have seen from the rover missions what fondness the general public have in their hearts for our robotic emissaries on Mars such as Pathfinder, Spirit, Opportunity and now Curiosity. Also look at how much interest and excitement there was for the Dawn mission to Ceres and the New Horizons mission to Pluto.

I am sure this would apply even more so to telerobots on the Mars surface operated by humans in orbit around Mars. For many I think that telerobots on Mars would be more exciting and interesting than a surface mission, especially if the reason for it is also well understood.

Biologically reversible exploration of Mars

The astrogeophysicist Christopher McKay has talked about the need for all exploration of Mars to be biologically reversible in the sense that, if necessary, we can remove all the microbes we brought to Mars, at least until we have a better understanding of Mars. He has also suggested that if we find a second genesis of life on Mars, biologically unique and different from Earth life, we might want to adapt Mars, to make it more habitable for native Martian life even if the result does not make it into a planet suitable for Earth life.

The idea is that if we find interesting life on Mars, we can remove all our contamination from the planet and leave it for the Martians instead - so that we can study the biology there, like having an exoplanet on our own doorstep. Maybe even get to restore the early Mars climate. Here is the same idea in his paper from 2007.

"Perhaps the most interesting and challenging case is that in which Mars has, or had, life and this life represents a distinct and second genesis. The discovery of a second genesis of life has profound scientific, as well as philosophical and ethical importance. Philosophically, the discovery would directly address the question of life in the universe, and would strongly support the idea that life is a naturally emergent phenomenon and is widespread and diverse in the universe. Scientifically, having another 11 example of life expands the scope of biology from one to two. There may well be significant advances in medicine, agriculture, pest control, and many other fields of biological inquiry, from having a second type of life to study. I would argue that if there is a second genesis of life on Mars, its enormous potential for practical benefit to humans in terms of knowledge should motivate us to preserve it and to enhance conditions for its growth. Observations of Mars show that currently there is no global biosphere on that planet and if life is present it is in isolated refugia or dormant. It is possible that life present on Mars today is at risk of extinction if we do not alter the Martian environment so as to enhance its global habitability.

"The utilitarian arguments presented above indicate that we should alter Mars to allow any indigenous life to expand and form a global biosphere even if the resulting biosphere is never a natural home for life from Earth or humans. If there is no indigenous life, these utilitarian arguments indicate that we should alter Mars to support life from Earth even if this never results in a biosphere that can be a natural home for humans.

"...This discussion has implications for near-term exploration of Mars by robots and humans. Until we know the nature life on Mars and its relationship – if any – to life on Earth, we must explore Mars in a way that keeps our options open with respect to future life. I have argued elsewhere that this means that we must explore Mars in a way that is biologically reversible. Exploration is biologically reversible if it is possible and practical to remove all life forms carried to Mars by that exploration. Because of the high UV and oxidizing conditions on Mars, biological reversibility is achievable.

"... Previous missions to Mars, such as the Pathfinder mission and the two MER rovers, have carried microorganisms to the martian surface where they remain dormant as long as shielded from ultraviolet radiation. To reverse this contamination already present on Mars, it would be necessary to collect all metal objects within which microbes could remain viable. Furthermore, the soil at crash sites and in the vicinity of landers that had come into contact with the spacecraft would have to be thrown up into the atmosphere where it would be exposed to sterilizing ultraviolet radiation. A similar approach can be used to reverse the contamination from human bases."

Quote from his Planetary Ecosynthesis on Mars: Restoration Ecology and Environmental Ethics

This was written some time back, in 2007, before the discovery of the many potential surface habitats we now know about, and before discovery of microbes capable of withstanding hours of the UV radiation on Mars. As you see he thought that it would be possible to reverse the effects of biological contamination after a human landing on Mars. He no longer thinks this is possible. It may still be possible for the robotic missions however.

Could we can send humans to the Mars surface in a biologically reversible way?

The only way I can see to do this in the near future, that could be given some reasonable guarantee of planetary protection, would be to use a metal sphere - that enters the Mars atmosphere at a shallow angle, so slows down to terminal velocity before hitting, with a human being inside. Then even if all systems fail, it would hit the surface at at most a few hundred miles per hour - in that case the human would not survive, but perhaps a sphere could be guaranteed to remain intact, or at least, not breached, after a crash on the surface?

Hollow spheres (rocket parts) that re-enter the much thicker Earth atmosphere survive intact to the surface. This hydrazine propellant tank from a rocket:

survives to the surface looking like this

(Space ball found in Namibia)

If all goes well, the human would land on Mars and then could be lifted off again - but of course can never leave the sphere or even look outside directly (as it is opaque), so I'm not sure if this would be thought worth doing. Another suggestion is to send humans to Olympus Mons.

Olympus Mons Caldera Region This might be the area on Mars most biologically isolated from the rest of Mars of anywhere, due to the thin air, high altitude, and the caldera walls. But it is a difficult place to land technically, and also - would even this be a biologically reversible place for a human base on Mars?

The idea is that it is so high above the surface that the air is very thin and there is almost no dust. This was suggested as a planetary protection measure in an article in The Space Review. It's a major challenge to do this with present day technology though, see Rob Manning's talk on the Space Show. In the space settlement article, they are suggesting a future with new technology with human bases already on Deimos. Some of the technologies Rob Manning mentions could be relevant such as deployable extending heat shields, or using larger parachutes than any of the ones tested supersonically to date. In any case, there's the same problem as with other human landings - we are unlikely to have 100% reliable landing systems. Even with your target the caldera at the summit of Olympus Mons, a failure during approach to Mars, entry, descent or landing could easily land you somewhere else. And would a human party - say inside the Olympus Mons caldera - really be biologically insulated from the rest of Mars? Also after a crash there? And would such a landing be biologically reversible in the future, if we need to remove the spores from Mars?

Yes, if there is anywhere on Mars, where humans can land in a biologically reversible way - or at least in a way that keeps the landing site separate from the rest of Mars, with only one area is contaminated - then Olympus Mons might be it. I think though, it would take a lot of research to be sure of this. If not biologically reversible, you have the possibility of an "oops" moment where you realize you have introduced Earth life to Mars, can't remove it, and have found a lifeform there you want to preserve or a biology such as ancient RNA based life, and can't do anything to prevent its eventual extinction.

Plants on Pristine Mars

You can put plant seeds on the surface, as these can be sterilized. You can grow plants with hydroponics and aeroponics. The difference here is that with hydroponics the plants grow directly in water, and in Aeroponics you use a mist, so it needs less water (which may be useful on Mars). There are different versions of these technologies. Some depend on micro-organisms but some do not. Instead of having micro-organisms you supply whatever the plant needs in chemical form in either water, or if it is aeroponics, in the mist.

The only life you have is the plant seed. You may use the Mars soil, or just use mist, depending on what you want to do. This microbe free version of hydroponics / aeroponics  introduces no risk of contaminating Mars so long as you do it with great care. The only thing  that will grow on Mars as a result of this experiment are these plants that you introduced to Mars. Here is a rather charming designer's concept for plants on Mars, called the "Little Prince Rover".

"Little Prince" rover designed to support a single plant on Mars. Since seeds can be sterilized (unlike humans or animals), these could be grown without any risk of contaminating Mars with Earth micro-organisms.

Named after the "Little Prince" who looked after a single rose on his asteroid in the fictional book by Antoine de Saint-Exupéry

It's possible that plants may be the first living Earth colonists of another planet.

So that introduces the possibility that you could have greenhouses on the surface of Mars and these could grow food for the colonists in orbit. They may have plenty to eat in their habitats anyway by then, but you could grow food on Mars too, maybe delicacies or things that grow particularly well on Mars or medicinal plants or whatever. Also you could have large plants, maybe trees (perhaps growing far larger in the Mars light gravity) or whatever else grows best on the surface of Mars.

Sadly, we can't apply these same principles to humans. If only we were like plants and could be grown from sterilized seeds. Well in principle, in the future, it could be possible by adapting the far future idea of "Embryo space colonization". If you could grow a human from an embryo in a sterile environment, and somehow supply them with all the nutrients they need without the symbiotic microbes we all have. Or else, engineer the microbes to make sure they can't survive on Mars. That is a far future science fiction idea however at present. And supposing it were ever possible, the Martian colonists would be vulnerable to Earth microbes if they ever left the planet, not being adapted to them, and anyone who left would not be able to return.

Perhaps there may be other future ways to do it. E.g. an impervious spacesuit or rover that can't be damaged even in a crash on Mars, that is also a biobarrier so that no microbes can get in or out and with the outside 100% sterile. This is way beyond anything we have at present however.

Biologically reversible exploration gives us a breathing space and leaves our future options open

The idea of biologically reversible exploration is to give us some breathing space, of a few decades, hopefully, to find out about Mars on a scientific level. To find out if there are habitats there for Earth life and search for exobiology. Meanwhile, you are also building up an infrastructure on Mars and in Mars orbit that would be useful if we did ever decide to send humans to Mars. Or indeed, it could be useful for other things too, anything we might do on Mars.

Perhaps you decide to try ecopoesis (duplicate the biological transformations of early Earth on much faster timescales), or you follow Chris McKay's proposal to turn the clock back to early Mars, or transform it in some other way, or even grow plants there (plants could be grown on Mars using sterile hydroponics without impacting on any native Mars life, since seeds can be sterilized). There would be many possible futures still open to you at that point.

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

What if the decision is to keep Mars biologically pristine for ever?

What if we find independently originated life on Mars, or amazingly interesting evidence of early stages that almost reached life but not quite? Should we leave the planet pristine to avoid contaminating it? That would be an exciting prospect seems to me. It's like having our own exoplanet, with its distinct biology, in our own solar system. The nearest terrestrial planet like that, other than Mars, may be light years away. Depending on future technological progress, it might be centuries before we have a similar opportunity - or if life is rare in our galaxy, maybe even millions of years.

I would say why not? Let's go all the way to Mars, and set up colonies in orbit around the planet, but never set foot on it at all, to avoid contaminating it. It is a bit like mountains that are left unclimbed out of respect for the mountain or local beliefs. Not too many of those but the mountains in Bhutan over 6000m are unclimbed.

This is possibly the highest unclimbed mountain in the world Gangkhar Puensum with an elevation of 7,570 m. All mountaineering is prohibited in Bhutan since 2004 out of respect for local religious beliefs.

This would be a future where you have agile rovers on the surface. and increasingly sophisticated humanoid avatars on the surface as well, directed and teleoperated by colonists in orbital colonies. It is a future where the Martian past and present turn out to be amazingly interesting, so much so, that humans never land on the surface in person, in their physical bodies, to preserve a biologically pristine Mars. I, for one, would find that an inspiring future to live in.

Collective sense organs for humankind on Mars

The idea that humans on the surface of Mars would 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 even as a topic for discussion. 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.

Generally those discussions are focused on the idea that we need to minimize the impact of humans on Mars. It is much rarer to suggest that it is a serious and significant issue which could be a reason to delay sending humans to the surface of Mars, or as a reason to go somewhere else first such as the Moon or the moons of Mars first. I think myself that it is just not good enough to do our best to exploit the brief window of opportunity of a few years before the first human landings or colonization attempts. We simply shouldn't risk destroying such a precious opportunity to make scientific discoveries, on the basis of ignorance, and there is no way we can do it on a basis of knowledge if the humans land on Mars in the 2020s or the 2030s. It is rare to suggest that, depending on what we find, and our decisions, we have a possible future where humans never land on Mars at all but explore it via telepresence instead.

In 1964, George Simpson wrote:

"There is even increasing recognition of a new science of extraterrestrial life, sometimes called exobiology-a curious development in view of the fact that this "science" has yet to demonstrate that its subject matter exists!"

That was before the Apollo landings. But though we have learnt so much by way of astrogeology, and have made great strides in understanding many things in the field of astrobiology, we are yet to shake off that major central issue. Andrea Rinalid in 2007 writes about astrobiology:

"Despite growing attention, the field is still haunted by the curse that evolutionary biologist George Gaylord Simpson voiced more than 40 years ago: “[T]his ‘science' has yet to demonstrate that its subject matter exists!” 

Now, 52 years after George Simpson wrote his paper, this could be our first opportunity to show that the subject matter of astrobiology exists. It could also possibly be the most major discovery in biology of the 21st century. How can we pass up on such an amazing opportunity and potential "super positive outcome" and ignore the potential issues of Earth microbes introduced to Mars?

Perhaps what we need is a change in the public's perception of how we explore space? 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

What do you think?

My Moon First books

This book has focused on the question of what happens if humans touch Mars and I have only briefly touched on what humans do if they don't land on Mars. But I go into this in a great deal of detail in my other books. I cover things such as the astronaut gardener on the Moon, the possibly vast kilometers wide lunar caves, ice at the poles with sunlight 24/7 nearly year round, and the value of the Moon for Earth amongst many other things. I see the Moon as a gateway and natural starting point for exploration of the solar system. That exploration can be open ended and lead eventually to human outposts throughout the solar system, in a collaboration where robots go to places where robots do things better, and humans play their part in ways where humans do it better, and the robots, as in "Where Biospheres Collide" are the mobile collective sense organs of humankind.

I've also been guest on David Livingston's The Space Show several times to talk about these ideas as well as the planetary protection issues for humans exploring Mars. See the list of my guest appearances on the show here.

If you are interested to learn more about this, please see my books:

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

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

Facebook group

I've made a new facebook group which you can join to discuss this and other visions for human exploration with planetary protection and biological reversibility as core principles. Case for Moon for Humans - Open Ended with Planetary Protection at its Core

See also

Robert Walker's posts - on Quora

And on Science20

 
Robert Walker's posts on Science20

Kindle bookshelf - for my author's page

And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon

Change log

6th January

• Added photographs of Solid 3 and of Dallas Ellman fine tuning a component of the astrobionibbler to In situ instrument capabilities
• Added mention of Let's Colonize Titan to Life in the oceans of Titan
• Work on Life in clouds of Venus