NASA currently has Mars sample return as their priority flagship mission not just for this decade but for the next one as well. They were recommended to do this in the 2012 decadal review. It is good for geology, nobody doubts that. But it is motivated mainly by the search for ancient life on Mars. Some exobiologists have warned that it is likely to be no more conclusive than the Mars meteorites we already have. They regard it as is little more than a technology demo for the search for life.

If you haven't come across this before I think you will find their reasons an interesting, and perhaps surprising read. So few people seem to be aware of this viewpoint of exobiologists. I have covered this in several previous articles, so if you've followed those, it may be a useful overview of the main points.

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. It is a matter of much controversy with many papers published on both sides of the debate, which is not yet totally resolved. 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.

So, first I'll go into this viewpoint in some detail. Then look into what the implications are for the Mars Sample Return and how best to do it. I'll suggest that it might well make best sense to sterilize the sample, and will explain why. Another option, if the sample is thought to have some potential biological interest (perhaps as a result of research from Exomars) is to return it to above geostationary orbit. Again I'll give the reasons for this suggestion. It's an op ed so a strongly stated point of view to stimulate discussion.


Their 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).

Though this paper is listed in the citations for the 2012 decadal review, it is never mentioned anywhere in the body of the text, and 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?

You'd think so. But it was not; it was just ignored. I'm not sure why this is.


You might well think it is easy if you haven't looked into it with this level of detail. Curiosity has already found organics. So we just need to return those organics and see if it contains life. After all, on Earth, wherever you find organics, you almost invariably find life as well. Indeed most organics on Earth originates from life.

But the thing is, as they point out in the paper, 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 don't know what stage of evolution we are looking for, whether it is modern DNA type life, early life with RNA only, an even earlier stage that is somewhere between what we call life and non life, or a radically different biochemistry. And we have no idea of the timeline, whether life evolved early on so that we are looking for large deposits of early life, or whether it evolved much later, or maybe was seeded by Earth billions of years ago perhaps after Mars lost its oceans, or even more recently. It may also have evolved and then gone extinct several times over, so that you'd need to find one of the layers of life between periods when it was extinct. We don't know if populations of microbes became huge as they did on Earth, or were small and localized. As Charles Cockell has pointed out in a series of papers, Mars may well have had many "uninhabited habitats" and may do so today as well, so in our search for life on Mars, we are not just looking for habitats for life, past and present, but also inhabited habitats.

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, or some other preferred habitat. 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.

We also don't know yet which Mars minerals were best for preserving ancient life. We can make some informed guesses but we may well get surprises.

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 apart 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?

Their paper goes into a lot more detail. What I said so far is more by way of background information to help you understand the context of the paper.

One of their main points is the importance of "follow the nitrogen". If you want to find out in more detail what their recommendations were to the decadal review, see my Will NASA's Sample Return Answer Mars Life Questions? Need For Comparison With In Situ Search, or read their paper.


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. As a result of the decadal review recommendations they have chosen to make Mars sample return their flagship mission for this decade, and then again for the 2020s as well. This will return less than one kilogram of rock.

To do an adequate survey in this way 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, as they were going to partner with Europe and send a suit of instruments called UREY. The exobiologists supported this 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, and to send new European designed experiments instead. There are no plans currently to fly UREY.

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. Exobiologists have designed many ultrasensitive labs on a chip and other instruments,in the hope that some day they may fly.

With increased miniaturization, the situation has changed radically in the last decade since the development of UREY.

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


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, thought to be in salty layers. The official line is that the liquid is always either 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.

"Life as we know it needs liquid water to survive. While the new study interprets Curiosity's results to show that microorganisms from Earth would not be able to survive and replicate in the subsurface of Mars, Rennó sees the findings as inconclusive. He points to biofilms—colonies of tiny organisms that can make their own microenvironment."
Mars liquid water: Curiosity confirms favorable conditions - Nilton Renno operates the REMS weather station on Mars, was also on the team for Phoenix and is an expert on potential Mars habitats.

It is also possible that there is life on the surface making use of the 100% humidity at night, similar to cyanobacteria or lichens, according to the research done mainly by the DLR Institute of planetary research in Germany. (See also Lichen on Mars for an overview).

Life that uses night time humidity in this way might perhaps be able to survive even in equatorial regions on Mars, with their frequent morning frosts. Gilbert Levin particularly thinks his experiments in the 1970s discovered life on Mars already - a minority view but one that has had additional support recently due to reanalysis of his experiment that uncovered evidence of circadian rhythms not exactly in sync with temperature changes, and with other features puzzling on the hypothesis of chemical reactions only. See Rhythms From Martian Sands - What Did Our Viking Landers Find in 1976? Astonishingly, We Don't Know.

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.


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 genetically 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?

That's not an academic exercise. Some scientists actually have engineered microbes to be able to produce inheritable DNA in an e-coil cell with a single foreign base pair involving two new bases, d5SICS and dNaM. This means it has six bases rather than four. They were careful to design them so that they couldn't reproduce "in the wild". It was able to inherit the new base pair for as long as the supply of foreign nucleotides was continued, after which the microbes replaced then with natural ones. See First life with 'alien' DNA. See also the Wikipedia entry about this research.

Though six bases DNA may well be harmless, I don't think many would be in favour of creating an organism with six bases that it can create in the wild outside the laboratory, and releasing it in the wild.

Now suppose the life from Mars is different in a much more radical way than that, as is surely possible. Maybe not based on DNA at all. Perhaps it 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 and other photosynthetic life in the oceans. Slowly at first, but if it has an edge, however small, it could eventually replace the Earth based phytoplankton completely. These are at the base of the marine food pyramid.

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 chemicals used by Earth life.

(As an example, when people eat BMAA, produced in green algae blooms, it can be misincorporated in place of L-Serine, and may be implicated in Alzheimers. Clearly this misincorporation is not a result of an adaptation of the green algae to cause Alzheimers, but rather, the result of an accidental similarity between BMAA and L-Serine.)

This is just one of many different scenarios but perhaps a particularly easy one to think about as an example.

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 environments where it could cause harm - impractical. And you also have to test it for long periods of time in case some problem crops up decades later. And it won't tell you if there is a chance it could evolve to be a nuisance later if initially harmless, for instance as it adapts to the Earth environment through genetic mutation.

In the case of unknown extraterrestrial life returned to Earth, it would seem that quarantine is no substitute for understanding what is in the sample and how it could adapt or evolve in Earth conditions.


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.

Though the putative Mars life wouldn't be adapted to attack us, our bodies would also not be adapted to recognize it as a threat.

This is an insight from the microbiologist Joshua Lederberg - nobel prize winner for his work on bacterial genetics.

Whether a microorganism from Mars exists and could attack us is more conjectural. If so, it might be a zoonosis to beat all others.

On the one hand, how could microbes from Mars be pathogenic for hosts on Earth when so many subtle adaptations are needed for any new organisms to come into a host and cause disease? On the other hand, microorganisms make little besides proteins and carbohydrates, and the human or other mammalian immune systems typically respond to peptides or carbohydrates produced by invading pathogens. Thus, although the hypothetical parasite from Mars is not adapted to live in a host from Earth, our immune systems are not equipped to cope with totally alien parasites: a conceptual impasse.


Robert Zubrin, and some others, have argued that because of exchange of meteorites between Earth and Mars that it is impossible that we have already been exposed by any Mars life Though he put it before (see Case for Mars chapter 5, section on back contamination, page 144). So I should look at this briefly because many of you reading it may have heard of it and been convinced by it.

However this has already been looked at carefully by the American National Research Council (NRC) study back in 2009. This reasoning, though interesting, is not sufficient to show that a sample return from Mars is safe.

The thing is, first that though we get many meteorites from Mars every year - they all come from relatively few impacts on Mars, roughly one every million years on average. The last impact on Mars large enough to send material to Earth, as far as we know, was around 730,000 years ago. All the material we receive at present has spent at least this long in the vacuum of space, also subject to cosmic radiation, and is expected to be thoroughly sterilized.

He also argues that any martian life, to harm Earth life, would have to be keyed to it. That is true of viruses, but not of other pathogens. For instance Legionnaires disease is a disease of amoebae. The microbes get inside the cell and eat it. They can do the same thing with the macrophagees - large white blood cells in our lungs that eat microbes and foreign matter. They eat the white blood cells from the inside. Once it is done, they then go on to eat other macrophages, one at a time. They don't need a "key to the DNA" indeed to them the macrophages are not much different from amoebae. In the same way, XNA based life might just eat our cells from the inside, and by Joshua Lederberg's argument, the cells not even recognize that this is harmful.

In addition, the habitats for life on Mars are likely to be fragile and not easy to send into space. For instance, how likely is it that surface salts and ices, or dust, would get here after an impact on Mars? Also, the rocks we get on Earth come from some meters below the surface on Mars, as those are the ones that reach escape velocity in the expanding crater, it so happens. They would not include any lifeforms in the surface layers.

And even though adapted to the harsh Mars conditions, it doesn't follow that all Mars lifeforms are space hardy enough to survive at least a century of passage to Earth in vacuum and cosmic radiation. Whether there has been any transfer of life or not, there may well be many species that have never crossed over, but would survive the much easier passage on board a sample return vehicle.

As well as that, the NRC looked at the fossil record and concluded that since many mass extinctions are not yet fully understood, you can't actually rule out the possibility that life received from Mars has caused mass extinctions on Earth in the past.

And the bottom line is that though we have experimental research and theory that suggests that transfer of microbes on meteorites is possible for some hardly lifeforms, we don't have a single actual example of a microbe that has been transferred between planets on meteorites, quite yet. It's just a bit early to be able to draw conclusions about what is and is not possible in a conclusive way.

For more on this see my "Does Earth Share Microbes With Mars Via Meteorites - Or Are They Interestingly Different For Life?"  and Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisited

The basic idea is a good one, of the "natural contamination standard" due to Richard Greenberg.

"As long as the probability of people infecting other planets with terrestrial microbes is substantially smaller than the probability that such contamination happens naturally, exploration activities would, in our view, be doing no harm. We call this concept the natural contamination standard."

From Infecting Other Worlds.

In that quote he applies it in the forward direction. But it works both ways, and we can also use it for investigations on Earth as well.

For instance, one application of it, we probably don't need to be too concerned about unearthing ancient microbes in ice or in deep subsurface water (Oldest water on Earth found deep underground). The reason being that this is an event that probably happens already as a result of natural events - not the actual piece of ice or the water we examine, but other deposits. So long as we are not adding significantly to the natural hazard, whatever level it is, then by the natural contamination standard we need not be concerned about planetary protection issues.

This standard is used for sample returns from asteroids. So long as they are small asteroids of the type that frequently hit the Earth's atmosphere, then if we return a sample from them, we are just doing something that happens naturally anyway. Indeed many times a year we get meteorite debris which will introduce whatever there is in the meteorites into our upper atmosphere. Which is clearly harmless as we are still here. So sample returns from asteroids and comets are listed as unrestricted Category V meaning that no special precautions are needed to protect Earth.

But in the case of a Mars sample return, what we are doing is not equivalent to any natural process, as the NRC discovered. So we can't use this standard to show that it is safe in the way we do for asteroid sample returns.


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.

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 that since it was so easy for Apollo, we could just do that again. If you haven't had it drawn to your attention you may have given this little thought, just assume it could be done.

But the lunar sample quarantine precautions were inadequate, not peer reviewed, not enforced, and had 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. And indeed there would be a need to consider human quarantine also because you have to have legislation for the scenario where someone inside the facility gets contaminated with the Mars material by accident.

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 of course be rushed to hospital, and there is no way that they would have let an astronaut even become seriously sick, never mind die, in the quarantine facility. They would have immediately dropped the quarantine regulations at that point. And many would say they should ethically. It's hard to argue that a human life should be sacrificed when you don't have proof that there is any threat at all for the rest of humanity.

For these reasons, human quarantine I think can never work when you don't know what you are quarantining against. It works just fine when you know what it is and its quarantine period, and how to identify it. if the human has the illness. But in a situation like this, for a sample return, the only solution is to make sure humans never come near a sample that could have extraterrestrial life in it.

Anyway, 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 because an uncontained sample return, however it got out of containment, could impact on them also.

Margaret Race of SETI looked into the legal situation in detail (indented so you can skip it if not interested in the details).

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.

For many more details - those are just some of the main points - see 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.


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 as some suggested in early studies back in the late 1990s.

The more recent studies say that to return that tiny less than one kilogram sample would require a new half billion dollar building involving a double walled containment technology never tested before (biohazard facilities use negative pressure to contain the material to be kept in. But it would also need to exclude even the minutest traces of all forms of Earth microbes as well, and that would require the double walled method)..

It would have to be finished well before the launch and the staff already trained many years in advance. With the lunar sample handling facility the facility was completed one year in advance and that is thought to be inadequate, from the experience of the many lapses that happened in that case.

I think it is unlikely that we have either that building or the legislation in place for a sample return in the mid or late 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

One of the things that makes it so expensive and difficult to build and to guarantee containment is that extraterrestrial life could be as small as 40 nm in diameter, possibly smaller. Well below the optical diffraction limit of 200 nm.

Each successive review has recommended lower size limits 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 obvious 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 an 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. It is one of the very few things we could do which could genuinely do this. Another very similar one is the creation of artificial life in a laboratory based on new biochemistry able to reproduce in the wild.

Which is not a reason to be scared. The reason for saying this is precisely to make sure we don't take these risks. They can only happen as a result of human actions, so we can prevent them.

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 returned from Mars "…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.


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

When the time comes, with:

  • 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%.

“The whole point of going [to Mars] and returning samples is that we don’t know what’s there and we want to find out,” Alex Sessions, of the California Institute of Technology, told Astrobiology Magazine. “This makes knowing how much contamination is acceptable a rather ambiguous task.”

“We want it [contamination] to be low enough to give us a good shot at seeing what we think could be there, without being overly conservative, which could cause the mission to be so expensive the whole thing gets scrapped.”

See How Much Contamination is Okay on Mars 2020 Rover?

So if you find amino acids in it, say, in only trace quantities, 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, if the sample probably won't contain life - and already has amino acids and DNA and other contamination in it from Earth - 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.


Or - perhaps a better solution - you could 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 it 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 in orbit, then 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? We mustn't send humans anywhere near it.

Instead study them with telerobots. Always send equipment 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.

You can also, return sterilized parts of it to Earth right away for the geological studies, in large accelerators and so forth.

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


Just to mention, this is another idea, which was covered in the NASA 2012 telerobotics symposium in the discussion of study of Mars via telerobotics. See the final report

In this alternative you return it to Mars orbit, to a similar situation, but humans in Mars orbit.

The 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 the simplest approach for planetary protection would be to ensure that 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.


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.
  • Safety for Earth, no planetary protection issues, so long as you make sure it can't impact Earth during the return journey to Earth. To achieve that you could use a biased trajectory, and of course you don't do aerobraking in the Earth atmosphere, but return possibly to a Lunar Distant Retrograde Orbit as for the Asteroid Redirect project - an orbit that goes alternately outside and inside of the Moon so appearing to orbit the Moon in reverse as seen from the lunar surface though prograde around Earth - a particularly easy orbit to get into when returning to cislunar space..
  • Saves on the $500 million cost of the Mars receiving facility
  • Yet close to Earth and easy of access
  • Turn around time of days or even hours for study of the samples, in principle. If you find something interesting in one experiment, you can send new equipment there. For experiments on the ISS, we are used to 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. However we get there, the actual flight time to the facility would be only hours from Earth.
  • Can still return sterilized geology samples to Earth 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 preparing 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. So we wouldn't have the same problem they had in the lunar samples receiving laboratory of many lapses of protocol because the engineers were pretty sure (though not certain) that there was nothing in it.


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.

It's rarely mentioned in the press. It was not mentioned in the decadal review. 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.

Everyone is agreed we should return samples, and that the best way to study them eventually is using Earth facilities. The advantages there are obvious.

The question is how and when. The exobiologists are just saying that in their professional opinion, 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.


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.

We could spend a decade or several decades passing laws to permit a sample return, 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.

It looks as if NASA and possibly China also will do these expensive sample return technology demos and geology missions.

Also, would they really spend ten or twenty years on that long process of legislation when there is probably only a small chance of life in the sample? I think when the time comes, surely they will just sterilize the samples, as a far simpler, less expensive solution.

Meanwhile, 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.

Then, as technology to send large masses to Mars improves, at lower costs, other parties will join in as well.

Eventually, if this reasoning is correct, and if there is life to be found there - then these in situ searches will be the ones to discover life there. 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.

Then, if they do find present day life on Mars, 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.

If they don't find life, it might make more sense to continue to sterilize the samples, just to be sure, not going to seriously impact on past life. But that's a decision that could be made at a later date, depending on what exactly they find with the in situ searches and further exploration of Mars.


This is an Op Ed for discussion. I have expressed my own views on the matter for discussion, also summarized some other views that you may find challenging as they go against the orthodoxy of the decadal review summing up.

The aim here is to stimulate discussion by presenting a challenging point of view for you to think about. The aim is not to try to persuade anyone else of these views.

Please comment below if you have any thoughts. Thanks!

Do also say if you spot any inaccuracies, typos, anything at all that needs to be fixed.

And if anyone knows, I'm interested to hear why it is the Decadal review summing up makes no mention of the white paper which is the main focus of this article.

As so often these days, this originated as my answer to a question on Quora, Why haven't we sent a robotic rock/soil sample return mission to Mars yet?.

See also


And you might like my other posts on Quora

Robert Walker's posts - on Quora

And on Science20

Robert Walker's posts on Science20


And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon