Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisited
    By Robert Walker | September 25th 2013 10:57 AM | 2 comments | Print | E-mail | Track Comments

    In my last article, "Does Earth Share Microbes With Mars Via Meteorites - Or Are They Interestingly Different For Life?" I talked about the NRC study, which looked at the same meteorite data as Zubrin, and came to the opposite conclusion that any life on Mars could be interestingly different. What are the implications of this for our plans to explore the solar system? Do we need to be careful about transfer of life to Mars or back to Earth?

    Could Martian life be harmful to Earth life?

    Zubrin has presented another argument here. He says that because Martian microbes have not adapted to infect humans that they can't be dangerous for us. Also that because they are adapted to Mars, then they won't be able to survive on Earth anyway except possibly in similarly cold and extreme places on Earth.

    Sadly both of those ideas have exceptions to them.

    Before I get into the details here, just want to say, the aim here is to prevent harm. So I'll talk about various possibly disastrous consequences of contamination of Earth or of Mars. The idea is that we should look at this clearly, and find out for sure if any of these disasters could happen. Then, if they are possibilities, we should make sure they won't happen.

    Zubrin's adapatation argument is an old argument actually. Carl Sagan looked into this in the 1970s, and it has been looked at several times since then, by the eminent microbiologist Joshua Ledeberg amongst others. You can argue both ways. You can argue that it has not evolved to infect humans. But you can also argue that humans have evolved no defences against Martian life.

    Joshua Lederberg wrote (in Parasites Face a Perpetual Dilemma)

    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.

    Diseases that jump from microbes to humans in one leap

    Yes many diseases of humans do come from animals or birds. However these are often most virulent when they first spread to humans, as happens with bird flu. It is not in the interest of the microbes to kill their host, so most diseases evolve to be less virulent. Indeed if they can prolong the life of their host, that is best of all. Eventually they may become symbionts.

    If you think about it, there has to be a first time that a particular microbe spreads to an animal host. So perhaps sometimes humans could be that first host. That has actually happened, because Legionaires disease is a disease of amoeba in the soil. It is able to jump in one leap from amoeba to humans, and become a disease of human lungs. This it seems is not advantageous to this microbe, at present, is more like an accident, and it surely has not adapted to infect humans, since it can't pass from human to human.

    A disease of Martian microbes might do the same thing. It may not need to adapt specifically to humans.

    Then there are many habitats on and in humans e.g. the skin, lungs, sinuses, that could be habitats for microbes, if our body does not recognise and deal with them. It could also be a disease of our crops.

    Extremophiles that can manage just fine in normal Earth conditions

    Then, the microbes could also out compete Earth microbes. There is no guarantee at all that a microbe adapated to Mars can't also adapt to warmer conditions. There are microbes in Antarctica that do just fine in warmer places.

    The other way around, when some scientists were looking for a microbe able to metabolize in low pressure atmospheric conditions similar to Mars they found to their surprise that one of the best candidates in their collection was isolated from human saliva (video talk). This microbe could actually do better at Mars atmospheric pressure than at Earth normal atmospheric pressure. There is no way it needed this capability to survive in its original habitat. But microbes do maintain their previous extremophile capabilities as they move to new habitats.

    Many archaea retain capabilities to withstand extreme heat that might have evolved in order to deal with boiling seas on Earth at the time of the late heavy bombardment, billions of years ago.

    Microbes on Mars are likely to have gone through a similar early stage when it was an advantage to have extreme heat tolerance in order to survive the impacts of the late heavy bombardment.Transmission electron microgragh (TEM) of Deinococcus radiodurans

    Radiodurans when it lives in soil or on clothes doesn't need its capability to survive in the high radiation fluxes of reactor cooling ponds or the extreme cold of Antarctica rocks. Yet it retains this capability through many generations and when the need arises, it can still survive in those situations.

    So there is no knowing what capabilities Martian microbes might have. Some of them might be better at coping with the Earth environments than life we have here already, just as rabbits do better in Australia than the native evolved marsupials. Or the other way around, some Earth life might be better than Martian life on Mars.

    If a Martian microbe takes over from an Earth one in an ecosystem, we don't know what will happen. Yes, it might make no difference, but it might behave differently from its Earth counterpart, and transform the ecosystem. It could so change things that other species go extinct. 

    It could compete with other organisms in the ecosystem directly, or consume or infect them. Or its products could poison them, or inhibit their activities, Or, it could simply be inedible, or poisonous when consumed, or it might be that the ecosystem has come to depend on products or capabilities of the microbe it replaces, which it lacks. Or it could be an allergen for animals in the ecosystem. There are many possibilities here.

    Exchange of DNA fragments with Gene Transfer Agents (GTAs)

    This is something that wasn't studied particularly by the NRC, but the later report by European Sapce Foundation made a special mention of it.

    If Martian life has a shared origin with Earth microbes, they may well be archaea - the oldest branch of the tree of life. These microbes have an extraordinary ability to share tiny fragments of DNA. In one experiment, researchers added GTAs able to confer antibiotic resistance into a sample of ordinary sea water and left it overnight. By the next day 47% of the culturable microbes in the sea water had taken up this antibiotic resistance capabilities from the GTAs.

    This means that the microbes don't need to be able to survive in Earth conditions to be a problem. If microbes die when they are returned to Earth, it may still be too late, they may have started this process of transfer of some of their DNA capabilities to Earth microbes already.

    The other way around too, microbes from Earth if they perish on Mars, may yet contaminate the DNA of martian archaea through these same Gene Transfer Agents.

    These GTAs are also tiny, just tens of nanometers across, well beyond the limits of optical microscopy.

    Has it happened already?

    The NRC looked into the possibility of harm to Earth caused by a sample returned from Mars. They asked the question, is it possible that microbes introduced to Earth from Mars by meteorites could have caused environmental disruption on Earth in the past. They came to the conclusion that though there is no evidence of this happening in the geologically recent past, it can't be ruled out for the most distant past.

    There are many unexplained mass extinctions in the past. How can we be sure that none of those were caused by martian microbes introduced on a meteorite?

    Worst case, goodby DNA (or goodbye XNA)

    Rotating DNA animation. Could life on Mars have a different backbone from DNA , using PNA, HNA, TNA, GNA or other XNA?This is more speculative, as it is not mentioned in either of the studies of back contamination of Earth. Here, I've brought together two things: the idea that life on Mars may have a different chemical basis, and recent reserach into the safety precautions needed for experiments involving XNA.

    The idea that Martian life could have a different basis from DNA goes back a long way, it was considered in the design of the 1970s Viking experiments, especially the Viking labelled release. Recently there's been new speculation that life on Mars could be based on XNA.

    Here XNA is a general term for nucleic acid analogues - with the same bases as DNA but a different "backbone", in place of the Deoxyribose of DNA. These include HNA, PNA, TNA or GNA (Hextose, Peptide, Therose or Glycol NA). The PNA world hypothesis for instance suggests that life on Earth went through an earlier stage where it used PNA (peptide nucleic "acid") before it started to use RNA or DNA. Life on Mars could have done the same.

    Mars life could also be different in other ways too such as mirror image DNA, or use different bases from DNA, or it might not be based on DNA at all. In Kauffmann's autocatalyitic set idea, life evolved from a group of chemicals that catalysed each other's formation, which, if true, leaves possibilities for such sets wide open, maybe there are forms of life we haven't yet thought of at all? Would we have thought of the possibility of all the complexities of RNA and DNA based life if we weren't DNA based ourselves?

    This whole idea of XNA based life was largely theoretical until a decade or so ago, but recently there has been much practical research by experimenters in laboratories. They have worked out ways that DNA could be transcribed into XNA and back again using enzymes. They have shown that XNA can evolve, following Darwinian evolution.. They now think that it might be possible to insert XNA into a living cell through genome transfer, and so turn a DNA based cell into XNA based life. This would be done by first adding XNA, which would coexist with the DNA, then removing the DNA.

    These experimenters take extreme care to make sure that their experiments can't impact on the environment of the Earth. Particularly if they ever do do this experiment to try to create XNA based life, then they would take care to make sure that the XNA can't be synthesized from resources available in a normal Earth environment.

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

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

    So, my question here is - since so much care is needed for XNA created in a laboratory, what about XNA returned from Mars?

    What if XNA is better at coping with Earth conditions than DNA?

    Also, as with the laboratory based XNA, it might also be non biodegradable by DNA based life forms. If so this might make it more persistent in the environment and impossible to get rid of.

    Or the other way around, contaminating Mars, what if DNA is better at coping with Mars conditions than whatever XNA there might be on Mars?

    Surely there are many questions to be looked into here.

    I think that if there is a new study similar to the NRC and the ESF studies in the past, they will probably spend a significant part of the report looking into the possibility of establishment of a stable XNA ecosystem in our environment based on Martian XNA, and whether this would be potentially hazardous to DNA based life.

    What about life transferred to Mars by a human expeidtion, would this cause problems?

    One of the big problems is that it compliates the study of Mars. There are proposals to send sensitive instruments to the planet able to detect a single amino acid in a gram of soil, or a single DNA molecule. If someone introduces life from Earth in the spacecraft, then these studies would be inconclusive.

    Then the introduced life could consume or out compete native Martian life. It might just coexist but it could cause extinctions. To do this before Mars is thoroughly understood is an experiment similar to introduction of rabbits to Australia in the nineteenth century. There is no way, on current knowledge, to predict the outcome accurately.

    Sometimes we need to be careful about microbes on Earth too

    When we travel on Earth, most of the microbes we are likely to carry to another continent would be there already (apart of course for diseases of humans, animals and plants). It is easy for many microbes to spread througout the planet through various methods, wind, dust, on birds, on debris floating in the sea, and so on.

    But some microbes for instance in the soil can't spread so easily. In the case of Antarctica,scientists and tourists have to clean their boots when they land on the continent, to reduce the chance of introducing foreign microbes to the continent, to preserve the unusual habitats theresuch as the microbes of the McMurdo dry valleys. The main focus is on tiny animals and plants, and diseases of wildlife, but microbial contamination of Antarctica is also an issue. Foreign microbes can transfer their DNA to local lifeforms even if they are unable to survive in the conditions themselves, and some may be able to survive in Antarctica.

    Lake Vostock, from space (NASA), this is a fresh water lake in Antarctica covered with an ice sheet 4 km thick. It is thought to be the most oxygen rich water on Earth, total darkness, and high pressure,
    Lake Vostock from space, the fresh water is 4 km below the surface but you can still make it out because the ice sheet above it is flat.

    Our closest equivalent to Mars is lake Vostock in Antartica. Scientists are taking cextreme care to study this lake in pristine condition and to make sure no microbes are introduced to it from present day Earth. And it has only been sealed beneath the surface for a few million years,.

    Mars is far more isolated from Earth than most habitats on Earth, far more isolated than lake Vostock for instance, with last possibility of a transfer from Earth to Mars tens of millions of years ago, and no certainty that it happened then. Was perhaps relatively easy for some microbes four billion years ago during the late heavy bombardment, but even then, you are talking about unusual microbes with interplanetary survival capabilities - the microbial equivalent of the birds, bats and insects in our analogy.

    Have we contaminated Mars already?

    In "The overprotection of Mars" the authors point out that present day spacecraft are not sterilized with the same level as Viking. This is true, and it is also true that there are thought to be many viable but dormant microbes on our spacecraft on Mars.

    However they do have a maximum of 300,000 culitvable spores per spacecraft. Those are the numbers when the spacecraft leaves Earth. During the voyage to Mars these numbers are reduced by cosmic radiation and UV radiation and the process continues on the surface of Mars.

    The theory behind these numbers is the Sagan Coleman equation. This has several factors to take account of reductions due to the voyage to Mars, whether the micro-organisms reach the surface of Mars, and so forth. The current aim is to achieve a probability of less than 1 in 10,000 of contaminating Mars in the current period of exploration of Mars (certainty cannot currently be achieved).

    So, since there is no certainty in the matter, yes,  it is possible that we have contaminated Mars, and especially so, since there have been failed missions such as crashes of orbital missions. However there is thought to be a good chance that Mars is contamination free, mainly due to the surprisingly harsh conditions that exist over most of the surface of Mars. The dormant life on our spacecraft most likely is just sitting on the surfaces, inactive doing nothing.

    If it has started to spread then with the harsh conditions on Mars, and life processes likely to be slow, it could be a localised contamination (slowly growing group of microbes in the vicinity of a lander). If so, perhaps that could be reversed. Once we start to send life detection experiments to Mars, one thing that would be good to do would be to examine the vicinity of one of our landers there, for instance Phoenix or the site of a crashed orbiter or lander, and see if there is any evidence of contamination, or if it has been kept pristine. 

    If it does turn out that we have contaminated Mars already with reproducing life, we should take even greater care to prevent further contamination. After you introduce rabbits to an island, by accident, that is not a good reason to then go ahead and introduce cane toads.

    Does this mean an end to Mars exploration

    No far from it. It just seems sensible to do exploration via telerobotics first. Indeed I would use almost all of Zubrin's excellent plans in his Mars Direct plan - except - that we send telerobots to the surface of Mars, rather than humans. The human habitats of Mars Direct can stay in orbit around Mars and can become the nucleus of a space colony of scientists and explorers in orbit around Mars, mining the Moons of Mars and NEOs for resources. .

    Image from the Telerobotics Symposium held in 2012, one of the recommendations was that telepresence be used to explore Mars during the early orbital missions.

    Telerobots on the surface can be operated from orbit by humans able to control what they do in real time The search for life on Mars would be done in this way too.

    As for Mars direct we can send feeder stock of hydrogen to the surface to generate many tons of fuel - but all of it can be used for exploration. There is no need to use any of it for return from the surface, since the telerobots can simply be left there.

    Indeed Zubrin himself suggested this approach in one of his mission proposals for a precursor to colonization - his double Athena mission. There are many other proposals like that involving a Molniya orbit - an easy orbit to enter from Earth wtih many benefits for telepresence operation on the surface of the planet.

    As for colonization, I've argued that Mars is simply not the best place to colonize right now. Yes it could be done but if the aim is to find a place where humans can make a start at space colonization, the Moon or independent space colonies close to Earth make much more sense. Colonies there are more likely to succeed, and less likely to end in tragedy.

    The main reason for choosing Mars over the Moon is the possible presence of life on Mars. But that is also the very reason why we shouldn't send humans to the surface at least until we are really sure about what we are dong and what the effect would be - and until we have a much more thorough understanding of conditions on Mars..

    In this it is no different from, e.g. quarantine regulations and the regulations that require visitors to Antarctica have to clean their boots. If you go to Mars, it is not enough to clean your boots. It seems likely that you will have to use telerobots to explore the planet, at least for now. But most likely what you do with your telerobot on Mars after that is up to you, so long as you keep away from any "science parks". There would probably be protected areas on Mars such as the warm seasonal flows, of exceptional scientific interest.

    Freedom To Colonize, Or Freedom To Explore Mars In Its Pristine State?

    If it turns out to be true that colonists inevitably introduce Earth life to the Mars, then, as I understand it, this would be prohibited under the current Outer Space Treaty. Any of its signatories could object on the grounds that it is "harmful contamination" of Mars under the terms of the treaty. Even countries that are currently non space faring nations could claim it is harmful to their future scientific investigations of Mars. 

    Almost all nations are signatories to this treaty, with a few exceptions such as North Korea.

    To prospective colonists, this treaty may seem unduly restrictive. If it turns out that the only way to keep Mars clear of introduced Earth life is to explore Mars using telerobots only, this means that colonists are not free to colonize the surface of Mars in person, at least for now.

    But there are many places on Earth where humans are not permitted to colonise or live permanently, and many regulations governing movement of species around the planet. These protect the freedom of everyone else to enjoy Earth without invasive species.

    This same law that could restrict colonization, also protects the freedom of scientists and explorers to discover Mars in its pristine state. It also protects the freedom of all of humanity to enjoy, and benefit from the stream of knowledge and discoveries that may come from study of pristine Mars.

    More of my articles, to find out more

    This is a follow on article from Do Mars And Earth Share Microbes On Meteorites, Or Would Mars Life Be Interestingly Different?

    For more about the potential value of Mars for humanity, see How Valuable is Pristine Mars for Humanity - Opinion Piece?

    For the back contamination risks: Need For Caution For An Early Mars Sample Return - Opinion Piece

    For more about whether to colonize Mars, or explore it, and what the alternatives are, see Ten reasons not to live on Mars, great place to explore

    If it does turn out that the surface of Mars is off limit for colonization at present, there are many other alternatives to explore - the Moon, orbital colonies around Earth or Mars, or indeed for the adventurous maybe eventually colonies further afield such as Jupiter's moon Callisto (- Category II according to the current COSPAR classificiation so a suitable place to colonize). In the more distant future, perhaps there may be many more colonists in space than there are on planetary surfaces. Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths

    See also

    Video talks

    This is a series short talks on contamination issues in my youtube channel on Mars and space colonization

    Recently I did some talks about whether we should return a sample from mars.

    The third talk in this series one covers much the same topics as this article, except that it focusses more on back contamination while this article focusses more on forward contamination.

    I've also done some video presentations with slides, on Reasons not to live on Mars, great to explore.

    Interesting (and easy to read) online papers and articles on search for life on Mars and possibility of a second genesis there

    What Is Life—and How Do We Search for It in Other Worlds? Chris McKay

    An Origin of Life on Mars - Chris McKay

    Invisible aliens: they’re not life as we know it — yet - Smart planet blog by John Rennie

    I'm Robert Walker, inventor & programmer. I have had a long term special interest in astronomy, and space science since the 1970s, and most of...

    View Profile


    Great read!:-) I have to admit pessimism regarding the power of international agreements to keep people from colonizing Mars over a_long_period of time in the future--IF there's clear benefits/resources to be gained there. I suspect on the scales of millennia governments would prove too unstable to prevent a contamination event that just has to happen once. I suppose though delaying colonization long enough to allow detailed examination of a pristine Mars would be some kind of consolation.

    Yes, I wonder about that also. If we have the technology to get to Mars surface easily in the future, so that anyone can get there as easily as someone can get to Antarctica at present - will someone go there?
    Is that the inevitable fate of our whole solar system also, Europa included for instance?

    Or, some mega technology solution to protect the planets? If so how does it keep going when civilizations collapse, if they do, during the collapse?

    Yes, delaying it would also help indeed, delaying it a century, or even, for some decades, along with vigorous exploration of Mars.

    Post new comment

    The content of this field is kept private and will not be shown publicly.
    • Allowed HTML tags: <span> <sup> <sub> <a> <em> <strong> <center> <cite><TH><ul> <ol> <li> <dl> <dt> <dd> <img> <br> <p> <blockquote> <strike> <object> <param> <embed> <del> <pre> <b> <i> <table> <tbody> <div> <tr> <td> <h1> <h2> <h3> <h4> <h5> <h6> <hr> <iframe><u><font>
    • Web page addresses and e-mail addresses turn into links automatically.

    More information about formatting options

    If you register, you will never be bothered to prove you are human again. And you get a real editor toolbar to use instead of this HTML thing that wards off spam bots.