Actually though it is a priority for NASA as it was recommended to them for the 2012 decadal review - many exobiologists would say that this is a mistake. It is good for geology - but it is being slated as part of the seaerch for life - and in this context it may be next to useless. The exobiologists see it as little more than a technology demo, which is likely to be no more conclusive for the search for life than the Mars meteorites we already have.

ALH84001 perhaps the oldest Mars meteorite we have, formed on Mars about 4 billion years ago, sent into space by an impact on Mars, and after millions of years in transit in space landed on Earth about 13,000 years ago.

Some still think that it preserves traces of ancient life, an early form of life smaller than any modern Earth cells. The study is very controversial. The exobiologists who are authors of the white paper submitted to the decadal review say that samples returned from Mars are likely to be as inconclusive for the search for life as this meteorite.

This study is in a white paper submitted to the decadal survey by eight exobiologists(from Scripps Institution of Oceanography, NASA Jet Propulsion Laboratory, SETI Institute, University of California Berkeley and NASA Ames Research Center). The decadal review ignored it. Though the paper is listed in the citations for the review it is never mentioned anywhere in the text, nor was it mentioned in any of the summing up speeches.

Given that the idea of the sample return is to search for life, surely the report of exobiologists, experts in the field, should have been given top priority and at the least, triggered a detailed investigation of whether the sample return would indeed achieve the stated objectives. But it was not, it was just ignored.

RAIN OF ORGANICS FROM METEORITES

The thing is, as they point out, that Mars gets a constant rain of organics from meteorites. So discovery of organics on Mars does not mean life. Indeed the organics Curiosity has found already are thought to be from meteorites, and the big surprise was that it didn't find them sooner.

Fragment of the Murchison meteorite, and particles extracted from it in the test tube. The meteorite was a witnessed fall, collected soon after it landed, and has many organics in it. It includes rare amino acids such as Isovaline:

Isovaline, a rare amino acid found in the Murchison meteorite. This helps confirm that the organics in it are of extraterrestrial origin as this amino acid is not involved in Earth life.

The organics from meteorites may even have a chiral excess also. In this 2006 analysis the EET92042 and GRA95229 meteorites had chiral excesses ranging from 31.6 to 50.5%.

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

So, if you send a robot to Mars to pick up samples based only on the geology and on detection of organics - then it is likely to return samples of meteorite organics like the organics already found by Curiosity. The rover they plan to send will not be able to distinguish meteorite organics from organics formed by life processes.

The sample return is intended as part of the search for ancient life. But the thing is,  that this rain of organics from meteorites has continued throughout the past history of Mars. There must be lots of ancient meteorite organics on Mars. And ancient life will deteriorate easily unless it is preserved in ideal conditions. As on Earth, but for different reasons,the ideal conditions will be rare and hard to predict.

You don't find fossils easily in an Earth desert. And fossils with organic remains in them are even rarer. There are ancient organics for instance in stromatolite fossils, but they are both extremely rare, and also, it took much research before they were accepted as genuine.

These are now known to be early stromatolites. But it took a lot of work and evidence before they were accepted as such. The proof involved discovery of minute traces of organics inside the fossils. Fossils with preserved organics from ancient Earth are exceedingly rare.

Organic fossils on Mars are likely to be just as rare and hard to find. For some of the same reasons and for some different reasons. The ground is far colder which prevents deracemization. That's the main reason we think there is a chance we can find ancient organics on Mars. There's a lot of potential there.

But though possible they are still likely to be rare and hard to find. First, the life has to be preserved in the first place, which requires conditions in which organics accumulate - and don't just get eaten by other lifeforms. For instance, perhaps in a lake bed or a salt bed. Most likely clays or salt deposits. Both quite fragile and vulnerable to later disturbance.

There might not have been much life in the first place. Often in places of Earth with little by way of life, places with similar geology in some cases have life and in others not, perhaps due to tiny changes in the microclimate.

We also don't know the capabilities of the life. We don't even know if we are searching for photosynthetic life or life that exists only around hydrothermal vents or geothermal hot spots. We don't know if the salt deposits are the place to look, or clay deposits, or both, or some geological formation that we haven't thought of yet.

On Earth one key to discoveries of early life was the realization that gunflint chert is a "magic mineral" that preserves traces of early life.

Galaxiopsis, one of the fossil microbes found in gunflint chert, which has turned out to be a "magic mineral" for search for evidence of early biology on Earth. What is the "magic mineral" for Mars? We've no idea and may need to return many tons of material back to Earth before we discover it if we rely on sample return.

Then once accumulated, the organics are easily washed out by later floods. Mars has had many flash floods. They can be decomposed by other lifeforms. They can deteriorate due to solar storms and cosmic radiation.

The last is the worst thing on Mars. If the rock has been exposed on the surface for three billion years, there would be nothing left except a few atoms of even meters thicknesses of organics, all split appart into component molecules by the radiation.

So first you are looking for a habitat that had life originally, and where organics from life were accumulating. Then you are looking for organics that were deposited in just the right conditions. Then rapidly buried to depths of at least ten meters - if it has been exposed on the surface for a long time before burying, the organics will be gone through cosmic radiation, even if later rapidly uncovered. Then it has to remain undisturbed through flash floods and erosion by dust storms still at a depth of ten meters at least. Then rapidly uncovered in the geologically recent past, e.g. rapidly excavated by an impact crater, or by wind erosion.

There may be deposits that match all those criteria. But you can't tell which ones do and which don't by geological methods. Not too hard perhaps to tell if it is rapidly uncovered, but the rest of the story, including whether there was life there originally, and which layer has life if you have multiple layers of clays as in some of the most promising areas for the search - that is either almost impossible or completely impossible to tell by geological methods.

Imagine trying to study this region by returning samples to Earth for analysis? And now, imagine that you also have to drill below the surface in each of the layers to find samples less affected by ionizing radiation? And now imagine that you have to return all those samples back to Earth for testing for biosignatures? And now add to this, that a deposit that contains life may have life signatures in some parts of the deposit and not in other parts of the geologically identical layer?

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

Perhaps you can see why the exobiologists think this is not an efficient way to search for life on Mars?

DOESN'T MAKE SENSE TO DO LOTS OF SAMPLE RETURNS

In these conditions it just doesn't make sense to search for life by doing lots of sample returns, ranging over square kilometers, picking up samples everywhere, and gathering so much of everything that you can be pretty sure to include any life if it is there.

Artist impression of a Mars sample return. NASA plan to send one mission on the 2020 launch window to collect and cache samples, and another some time in the 2020s to collect the cache and return it to Earth.

The cache is unlikely to contain samples of early Mars life according to the exobiologists, requiring dozens of these missions to have a decent chance of success.

This mission would return less than a kilogram of material from Mars at a cost of millions of dollars per gram.

NASA do one high cost "flagship mission" in each decade.

It would be immensely expensive.  It would take decades to explore just one small region as you follow up on ambiguous results just to find out that they are false leads.

And you might well still miss the one habitat with preserved life, which need not be geologically remarkable.

Instead you need to send in situ rovers with the ability to drill deep, to get below the effects of cosmic radiation. And able to examine many deposits, as we have no idea where the life would be preserved. In clays? In salts? In the remnants of hydrothermal vents? Only particular layers as you dig down?

That is the strategy of ExoMars. And the exobiologists support this strategy.

NASA originally planned to use this strategy too, they were going to partner with Europe and send a suit of instruments called UREY. Which the exobiologists supported as the right way ahead.

Sensor Being Developed to Check for Life on Mars

But they pulled out of that project, leaving the ESA to partner with Russia instead.

Then as a result of the decadal review they decided to do this sample return instead, against the advice of the exobiologists. The authors of the white paper include exobiologists who worked on the UREY project.

Work has continued on a successor to UREY even with no expectation that it will be sent to Mars in the near future. There are also many other ultra sensitive life detection instruments we can send, labs on a chip. The situation has changed radically in the last decade since the development of UREY.

• Astrobionibbler - similar idea to UREY, smaller, later development. Able to detect a single amino acid in a gram of soil.[
• 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.
• LDChip and Solid3, 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
• 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.
• 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

This is for present day life. On the perhaps remote chance that there is present day life in the Mars equatorial regions, they could detect the 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).

For details see my Will NASA's Sample Return Answer Mars Life Questions? Need For Comparison With In Situ Search

PLANETARY PROTECTION ISSUES

Then there are also many planetary protection issues involved with returning a sample from Mars. After all what you hope to find there, best case scenario, is some unknown non terrestrial biochemistry.

And though the place where Curiosity is searching is not a likely place for present day life - and many say it is impossible there, others are not so sure. They already discovered a subsurface liquid layer, indirectly, in the sand dunes in salt deposits. The official line is that it is too cold for life, or too salty. That it achieves the right salinity, and the right temperature, but never both at the same time. However other exobiologists say that it may be possible for it to be habitable through life creating microclimates. It is also possible that there is life on the surface making use of the 100% humidity at night.

It is not at all certain and not nearly definite enough to return a sample on the hope that it contains present day life. But even if it is just a 1 in a 100 risk, or a 1 in a 1000 risk, it means that you have to take full precautions to protect Earth against return of present day life from another planet with alien biochemistry.

BUT MARS LIFE COULDN'T POSSIBLY HURT US? COMPARISON WITH ARTIFICIAL LIFE MADE IN A LABORATORY

So then - many say - that it couldn't possibly hurt us, being adapted to Mars. But now, just twist this around a bit. Instead of extra terrestrial life from Mars, suppose it is artificial life made in a laboratory on Earth. We are cautious even about releasing geneticially engineered life. But this potentially could be life with a different biochemistry, for instance, perhaps six bases instead of four for DNA. Do you think we should do that? Most people would say we shouldn't take the risk. That's not an academic exercise. Some scientist actually have engineered microbes to be able to produce inheritable DNA with six bases rather than four. They were careful to design them so that they couldn't reproduce "in the wild".

Now suppose the life from Mars has a more efficient metabolism. Or is better at photosynthesis. Or both. Then there's a possibility that it could, if released accidentally into the sea, take over from the Earth based green algae. Slowly at first, but if it has an edge, however small, it could eventually replace the Earth based green algae completely. And then maybe it is inedible by Earth life or even poisonous. Not through adaptation or design obviously. But because being based on a different biochemistry, it just is not edible to Earth life, or else, even produces chemicals that are poisonous or misincorporated due to resemblance to Earth life.

So we really have to take a lot of care with sample return. And - quarantine is no good. Because to check it is okay then we have to test it with all the environmments where it could cause harm - impractical.

COULD HARM HUMANS

It could also be harmful to humans too even. Our immune systems respond to chemical signatures such as peptides and carbohydrates to identify foreign life. If those aren't present, the life could just invade our bodies and they would not recognize them as harmful, no more harmful than, say, an artificial heart. We might have no immunity to it at all. Or our plants or animals ditto. This is an insight from the microbiologist Joshua Lederberg

MANY LAWS TO PASS, DOMESTIC AND INTERNATIONAL - TAKE AT LEAST A DECADE JUST TO PASS ALL THE LAWS

So, as a result, there are many laws that would have to be passed before a sample can be returned, and a long period of public consultation. Many internal domestic laws in the country returning it - in case of the US it's a long process.

The lunar sample returns may make it seem easy because they passed the law on the quarantine regulations on the very day of launch of Apollo 11 giving nobody any opportunity to scrutinize it or recommend changes even.

This shows the crew of Apollo 12 in an open dinghy on the sea and behind you see the hatch wide open. The interior was dusty with Moon dust which got everywhere as the astronauts reported. If there was any life in the lunar dust, which at the time was thought unlikely already, it would have got into the ocean at this point.

Shows the Apollo 12 astronauts' wives outside the quarantine facility. Both photos from When Astronauts Spent Thanksgiving in Quarantine for Fear of Moon Disease

After that, and several other quarantine breaches, all the lunar quarantine procedures like this were mainly for show. They would have done almost nothing to protect Earth, even according to the scientific understanding of the time.

Indeed, one of the issues identified was that the scientists and the management both didn't take the procedures seriously. In addition to this breach, also the astronauts walked across a deck lined with personal who would be exposed to any dust on their suits - and there was a clear breach of protocol in the sample quarantine lab. It's thought that there were probably many other unreported breaches of protocol.

One of several concerns for a Mars sample return is that many of the scientists and management involved may treat it as mainly for show in the same way, not be strongly motivated to enforce the tedious protocols, as they would be almost certain there is no life in the sample, much as for Apollo. If you do that, you might as well not build the facility in the first place.

For more about this: see Lessons Learned from the Quarantine of Apollo Lunar Samples

I think many who haven't looked into it might imagine something like that, it was so easy for Apollo,just do that again.

But the precautions were inadequate, not peer reviewed, not enforced, many lapses of protocol. Though Mars sample return would not involve humans directly, there would still be many opportunities for human error or accidents or even deliberate interference to lead to breaches of the protocols.

In any case there was no scientific justification for the length of the quarantine period. The latency period for some diseases such as leprosy is measured in decades. And what about microbes that have other effects, not on humans? And what would happen if the humans became ill? They would be rushed to hospital, and the quarantine regulations dropped at that point. Human quarantine I think can never work; the only solution is to make sure humans never come near a sample that could have extraterrestrial life in it.

Anyway, that would never be permitted nowadays. The laws have been rescinded. And what they did with Apollo 11 would not be permitted nowadays. You can't expect to just pass a law on the day of launch of the sample return mission, and that's it done, as was the situation in the 1960s.

Also there are many international treaties to be considered, which were not present back then. Also internal domestic laws of other countries could also be relevant.

Margaret Race of Seti looked into this

She found that under the National Environmental Policy Act (NEPA) (which did not exist in the Apollo era) a formal environment impact statement is likely to be required, and public hearings during which all the issues would be aired openly. This process is likely to take up to several years to complete.

During this process, she found, the full range of worst accident scenarios, impact, and project alternatives would be played out in the public arena. Other agencies such as the Environment Protection Agency, Occupational Health and Safety Administration, etc, may also get involved in the decision making process.

The laws on quarantine will also need to be clarified as the regulations for the Apollo program were rescinded.

It is also probable that the presidential directive NSC-25 will apply which requires a review of large scale alleged effects on the environment and is carried out subsequent to the other domestic reviews and through a long process, leads eventually to presidential approval of the launch.

Then apart from those domestic legal hurdles, there are numerous international regulations and treaties to be negotiated in the case of a Mars Sample Return, especially those relating to environmental protection and health. Domestic laws of other states might also be invoked and need to be negotiated.

She concluded that the public of necessity has a significant role to play in the development of the policies governing Mars Sample Return.

Margaret Race:   Planetary Protection, Legal Ambiguity, and the Decision Making Process for Mars Sample

see also my Mars Sample Return - Legal Issues and Need for International Public Debate

When you look at what is involved, and then bear in mind how even a simple change in the law can often take ten years by itself - you can see it is likely to be a long process.

HALF BILLION DOLLAR PURPOSE BUILT RECEIVING LABORATORY TO RECEIVE THE ONE SMALL SAMPLE RETURN

As well as that if you look at the requirements for a sample receiving laboratory - well it's not a simple glove compartment in a biohazard 4 facility. Just to return that tiny sample would require a new half billion dollar building involving technology never tested before. It would have to be finished well before the launch and the staff already trained. I think it is unlikely that we have either that building or the legislation in place for a sample return in the 2020s.

One of the designs submitted for consideration for a Mars sample return facility. In this version of the facility, all the sample handling and inspection is done using telerobotics controlled from outside the heart of the facility. For my summaries of the material from the United States National Research Council, the European Science Foundation, the Office of Planetary Protection and other mainstream studies see Mars Sample Return - Legal Issues and Need for International Public Debate

Extraterrestrial life could be as small as 40 nm in diameter, possibly smaller. Well below the optical limit. Each successive review has recommended lower size limites based on newer research. latest Mars sample return review by the ESF recommended that it should be able to contain particles as small as 10 nm in diameter for safety for a Mars sample return.

The problem is that you have no idea what is in the sample. It is easy to contain a known hazard like the smallpox virus, say, or anthrax. It is extremely difficult though when you have no idea what it is you need to contain and have to design it to contain all forms of terrestrial life and not just that, also possibly unknown forms of extraterrestrial life that could be smaller than any known Earth lifeform and possibly undetectable in many tests for Earth based life. such as DNA sequencing.

So, it's not as simple and obvous as it seems to geologists and most who think about this apart from exobiologists and those who have looked into it really thoroughly.

And the thing is - that it is one of the few genuinely existential risks. A giant asteroid impact could not make humans extinct. We are a very adaptable species able to survive in the Arctic, or the tropics, with minimal technology. Turtles, crocodiles, small mammals, flying dinosaurs ancestors to the birds, and dawn redwoods all survived the impact. So humans with technology surely would also. Asteroids can also be deflected given enough warning.

But - extra terrestrial biology, like artificial life created in a laboratory, could potentially make humans extinct. This chance as well as other possible risks from life returned from Mars may be small (we have no way to assign a probability but most think it is a small, but as Carl Sagan said, in the context of discussion of human pathogens "…The likelihood that such pathogens exist is probably small, but we cannot take even a small risk with a billion lives."

I have two ideas for how this may pan out.

STERILIZATION IDEA

First, I think it is very unlikely that the US will return an unsterilized sample from Mars myself.

When the time comes, the expense, the long legal process, probably objections from those concerned about safety - I think they will just give up and return a sterilized sample. Especially since it is unlikely to contain life in the first place. I hope so anyway. Because the risk doesn't seem worth the return.

They have already said that they will not sterilize the sample return container for Curiosity's successor 100%. They will sterilize it to a high standard, but not 100%.

So if you find amino acids in it, say, you'll never know if it was from Mars or Earth. That's the same problem that plagues study of Martian meteorites, that objectors can always say that perhaps the organics got into the meteorite on Earth.

So - they are not being very serious about the search for biosignatures anyway. This makes it clear that their main priority is geological plus a technological demo, or they would make sterilization a top priority. It is not something it makes sense to economize on if your priority is biosignature detection. So, why not just sterilize the sample itself on the return journey from Mars?

Use an ionizing radiation source, send it in the ship that picks up the sample from Mars orbit - and blast it with the equivalent of perhaps a hundred million years of radiation on Mars (or whatever is judged adequate)?

That won't make much difference to the geology and you can take account of it in the analysis.

On the remote chance it does have present day or past life - then it also won't make much difference to the past life. It's going to be a sample from the surface so even if a young sample not likely to be so young that  a hundred million years worth of present day Mars surface levels of radiation will matter, and even if recently exposed, chances are that it was on the surface for many hundreds of millions of years at some time in the past before it was buried. And for present day life, you can tell that it was there via biosignatures that would still be readable after sterilization, on the low chance that there is present day life in the sample.

Then it is a technology demo, and also, of value for geology, but not a planetary protection issue. Then you don't need the legislation, and the sample return building and all that. So a huge saving, 100% planetary protection, and no loss in geological value and little by way of impact on past life detection on the remote chance it is there, and you still detect present day life if it was there - except of course that with the minute traces expected for both past and present day life the contamination due to inadequate sterilization would probably make them ambiguous anyway.

RETURN TO TELEROBOTIC FACILITY ABOVE GEO IDEA

Or - perhaps a better solution - return it to above geostationary orbit. There, it's at maximum delta v from Earth and from the Moon. And study it only telerobotically. By then surely we can send hundreds of tons into geostationary orbit easily. So won't be a big restriction. Almost any experiment except ones involving large particle accelerators, can be done up there in orbit.

But don't send humans there. Because once humans are involved you then have the vexing issue of quarantine, that no quarantine period is long enough, because of latency periods, and because anyway the microbes or whatever they are might not even be an issue for humans at all but could be carried back to Earth by them. And in any case, if a human astronaut became ill what do you think mission control would do? They wouldn't just leave them in orbit to die from what could be some simple Earth based illness. They would immediately as top priority emergency return them to Earth and then what value is the quarantine period?

Instead study them with telerobots, always sent one way only, to the orbital facility which would gradually grow as more and more scientists send equipment and telerobotic modules there.

That is until you know what is in the sample. Once thoroughly understood you can return it to Earth. Or if you can sterilize it, return sterilized parts of it to Earth/

I think we should do something like that if we return a sample to Earth's vicinity.

STUDY IN MARS ORBIT IDEA

Or alternatively return it to Mars orbit, similar situation, but humans in Mars orbit - advantage there is that there is much less time for the sample to deteriorate if it has present day life and you don't know for sure how to sustain it. Once again - humans never go near the sample itself which remains in a separate facility. Obviously this is not for the 2020s sample return but for some later date when we may have humans in Mars orbit.

STUDY IN SITU BEST RIGHT NOW

But I think it is far better to study Mars life in situ. And treat the NASA mission as just a technology demo - at least for the search for life. Unless ExoMars discovers present day life.

If ExoMars does find present day life, I think it may then become clear to everyone that extensive precautions are needed, and perhaps then this idea of a telerobotic study in a high orbit just above geostationary orbit may then seem a good way to do it. Remember we can already do surgery via telerobotics and by then it will be very much advanced.  We may well be exploring the Moon via telerobotics just as we do ocean floors

The advantages of return to a telerobotic orbital facility are

• No need to pass any new legislation, so can do it at least a decade sooner - given that there is no move to start that process yet - I expect they won't start on it until a return is imminent some time in the 2020s, meaning an unprotected sample return to Earth is unlikely until the 2030s at earliest, and quite possibly not until the 2040s or later, just to allow for passing all the legislation.
• Total safety for Earth,no planetary protection issues.
• Saves on the $500 billion cost of the Mars receiving facility
• Yet close to Earth and easy of access
• Turn around time of days or even hours. If you find something interesting in one experiment, you can send new equipment there. For experiments on the ISS, then it is a longer turn around, months, because of infrequent flights. But by the late 2020s when we could expect a sample return, then we may well be able to send hundreds of tons with just a few days of warning. For instance using Skylon, able to fly directly into space, and several other similar proposals.
• Can still return sterilized geology samples to look at in particle accelerators

Once we have a clear idea of what we have in the sample, either from in situ study or from telerobotic study, then we can try the long process of passing laws and devising facilities to return it to Earth. That is if it contains life independently originated or evolved for some time independently of Earth on Mars.

At that point the need for caution would be clear to everyone and so they would take a lot more care, less chance of human error. And as well as that, we would already know a fair bit about it, so it is no longer prepairing for all eventualities in an unknown hazard, but a known hazard. That might well simplify many things. And make the legal process simpler and make it easier to know that it is safe and that you are taking the necessary precautions.

Or you might find out early on that there is no life in the sample. At that point, just sterilize the whole thing, as a precaution just in case, then return it to Earth. No need for legislation as there is no need for new legislation to return a sterilized sample to Earth. In that case, there is almost no delay.

Some of the proposals for sample return from Mars already see the sample returned to a module sent to a high orbit around Earth or the Moon to receive it and return it to Earth, to deal with issues of preventing sample container damage during the return to Earth. This approach is similar - collect the container in lunar orbit or above GEO. But then, instead of returning to Earth, study it in situ using instruments sent in the retrieval spacecraft. Then if the results are pretty conclusive that there is no life there - already - then just sterilize and return to Earth. If ambiguous, then sterilize part of it and return for geological investigation, e.g. in particle accelerators and continue to study the rest of it in the facility which would expand with more instruments and modules, especially if traces of present day life is found there, until it is thoroughly understood.

If extant life is found, viable also, on that remote possibility, then decisions are made based on what is found. If considered extremely hazardous, the facility becomes a nucleus of a new telerobotic research facility in orbit. And at any rate in that case, those concerned would take extreme care as by then they know what is in it and will take as much care as they would for artificial life in Earth labs.

I wrote this because the work of the exobiologists on this topic is little known even amongst many who are expert on Mars space exploration issues generally, and even amongst the geologists working on the missions.

For some reason this viewpoint is just not heard much at all and I think it needs to be more widely known and discussed. At the very least I think their white paper should have triggered a full review by the decadal review for a proper comparison of the two approaches, which has never been done. They should at the very least have recommended such a review, even if they endorsed the sample return as their favoured option subject to review. I have no idea why this was not done and why the paper was never mentioned, a paper by mainstream reputable exobiologists who had worked on the only recent NASA project to design instruments to send to search for life in situ.

Anyway given that NASA is now committed to a sample return, perhaps the ideas suggested here could be used to make sure it is safe as regards planetary protection - and at the same time preserve its value for geology, and as a technology demo.

And everyone is agreed we should return samples, and that the best way to study them eventually is using Earth facilities. The question is how and when. The exobiologists are just saying that we have not yet reached the stage where this is the way to go.

As they say in their paper:

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

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

They are not saying that we should never do it. They are just saying that in their professional opinion as exobiologists, this is not the right time to do it.

From the point of view of planetary protection also, it is far easier to protect against known hazards than to try to cover all the bases and design a facility that is able to contain any form of exobiology, no matter how exotic, that we can imagine might possibly exist on Mars. That's why the receiving facility is so expensive, and yet also, still possibly inadequate, because we have no idea what it would need to contain until we can do some in situ study on Mars first to find out what it is we need to protect against, if anything.

And without the in situ search for biosignatures, we could pass that decade or several decades of laws, build a half billion dollar facility - and then discover at the end that there is no life in the samples and that we discover no more than we could have found out if we just sterilized it in the first place.

What I expect to happen, just venturing a guess here, is that while NASA are doing these sample return demos - possibly China also -and probably sterilized as the easiest way to comply with planetary protection issues - that ExoMars and its successors will continue to search for life in situ. It may be joined by other countries that see this as a better strategy - both Japan and India have been interested in Mars and India successfully sent an orbiter there, and more likely to do in situ searches than the much more expensive sample returns. As technology to send large masses to Mars improves, at lower costs, other parties will join in as well.

Eventually these in situ searches will be the ones to discover it, maybe not the first mission but one of them. At that point then it may well turn out to be a good thing that NASA has developed this sample return technology. But then it would be return of a known sample.

And if they do find present day life, then everyone would recognize the importance of sample containment and they would take it seriously. In that case the idea of a telerobotic temporary, and possibly permanent facility in a high orbit above GEO may become very attractive. It would not require any new legislation to be passed, but could be covered by COSPAR workshops approving the idea.

See also

• Why Phobos Might be the Best Place to go for a Sample Return from Mars Right Now
• "Super Positive" Outcomes For Search For Life In Hidden Extra Terrestrial Oceans Of Europa And Enceladus
• Mars Sample Receiving Facility and sample containment
• Mars Sample Return - Legal Issues and Need for International Public Debate
• Need For Caution For An Early Mars Sample Return - Opinion Piece
• Will NASA's Sample Return Answer Mars Life Questions? Need For Comparison With In Situ Search