Lisa Pratt, the new planetary protection officer for NASA takes up her job at a challenging time for astrobiology. We are approaching a major decision point for Mars. If Elon Musk succeeds in his ambitious plans, then some time in the next couple of decades we may introduce trillions of hardy microbial spores to the planet. Not deliberately, but just because we can't help but take them with us wherever we go. This is a major quandary for astrobiology, and for anyone who is fascinated by questions about the origins of life as well as those who would benefit from those discoveries indirectly. 

First we need to deduce if there is any life currently living there, and if so, what its capabilities and vulnerabilities are. But the thing is we need data before we can deduce anything - because of the difficulty and expense of getting to Mars and of our spaceships surviving the landing. Russia, and ESA both tried, but only the US has had successes with Mars landers, and it has had failures too. We haven't sent life detection instruments to Mars since the 1970s, although astrobiologists have developed many instruments that could be sent there, some "ready to fly" or close to it.

So what can we do? My solution is to be even more ambitious in the field of human spaceflight. To set our sights further afield, to the asteroid belt, Callisto, Titan, and beyond. Though we should start with the Moon as the closest, easiest and safest (but hardly safe) place to go which also has turned out to be of far more interest than it seemed to the Apollo generation, and has been dubbed our "eighth continent". If we do it like this we can have the patience and the time to explore Mars properly and do the science there. Then we can decide how to explore Mars based on knowledge of whether there is life there, whether there are habitats, and with some understanding in advance of what might happen if our two planetary biospheres collide.

We have no experience of biosphere collisions between possibly independently evolved life on different planets. It might be that they rarely cause problems. It might be that they almost always do, making species extinct or degrading each other through chemicals that get misincorporated, or parts of the biochemistry or its byproducts that are toxic to the other biosphere. I don't think any astrobiologist today could answer that with complete confidence. At least, not until they can study the Martian life if it exists. Then they could start to work through what the consequences might be.

This article starts by presenting the broader vision for humans in space, and the discussion of the astrobiology continues after that in the section: The astrobiology quandry for Mars .

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I think humans in space are a great thing to aim for, as explorers, scientists and tourists to start with, science bases, as for Antarctica, and small settlements, and eventually colonies in space. Robots may do it better to start with but it is still far easier to explore Antarctica with humans rather than telerobots, and the only way to find out the potential for humans in space is to give it a go. Once we have self sufficient closed system habitats it may be much easier to maintain humans in space even for many years at a time with little or no resupply from Earth. At that point, the whole solar system will be open to us, with hardly any more initial outlay for a mission to Neptune or Pluto than for Mars or Venus, and the advantages of humans in space may really start to shine.

But we have to do it responsibly. Mars is a planet that many have set their hearts on, and now happens to have huge planetary protection issues. There are many other places we can go to that have no issues at all. Also the Moon is by far the easiest celestial body to visit first, with much to explore. I happen to think a settlement on the Moon is far more likely to succeed than one on Mars for multiple reasons, including easy access, and low cost exports. We can develop methods for sustainable habitats there and so open the entire solar system to humans through our human factors researches on the Moon and experiences of what it is like to live and explore in a deep space environment on a planetary surface, our "Planet Moon" as some planetary scientists like to think of it.

So that's the background to this article. Here are some of my earlier articles, and an online book, to explain this background in a bit more detail.

  • Case For Moon First: Gateway to Entire Solar System - Open Ended Exploration, Planetary Protection at its Heart - this is the key one, an online and kindle book in which I set out the main vision of open ended exploration, starting with the Moon, with settlements further afield, and eventually to the outer edges of the solar system, but in a way that respects the value of science and follows principles of planetary protection, to not be a nuisance, and to try to pass on a solar system to our descendants with the same or more promise as the one we have today.

    Which doesn't mean a prohibition on humans ever landing on Mars, say. It means finding out what is there first and then evaluating what the result would be of the clash of the two biospheres, before making the decision about whether to send humans there, or explore it from orbit via telepresence a bit like a game of "Civilization". 

Mars is far more like the Moon than like Earth, and this is not likely to change any time soon. The Mars Trilogy is science fiction based on ideas from the 1980s. Kim Stanley Robinson himself says, that based on current research, Mars could not be terraformed in as quickly as a few centuries, if at all.

In the thin atmosphere you couldn't take a single breath. The water lining your lungs boils, so you can't even use whatever air is in your lungs (best advised to breathe out right away as the air is useless and can damage your lungs as it expands). You are unconscious within 15 seconds, lasting only for as long as the oxygen dissolved in your blood lasts. Full body spacesuits are eye-wateringly expensive and even if we achieve a tenfold reduction in cost, it's $200,000 each. They need constant maintenance, replacement of the fabric, and still only last for a couple of dozen EVAs doing light work outside the ISS. They are sometimes compared to a mini spaceship, they are so complex, and preparations and safety checks before an EVA on the ISS start the previous day.

Living on Mars would be much like living as an astronaut on the Moon. Indeed spacesuits for Mars would work as well on the Moon, and the Mars rovers and habitats also. And the Moon even seems to have ice at its poles now, and not just bound up in the rocks, but as ice crystals, though we don't know yet how easy it is to extract. It is also so close to the Earth that material exports are possible. Also tourism, visits home, and medevac to Earth for medical emergencies. So why not start on the Moon?

Then recently I've been exploring the idea of humans to Titan in the Saturn system. To Callisto first, in the Jupiter system, then Titan.

Callisto is already passed as planetary protection category II which makes it is okay for human settlement. It is a far better refueling stop and settlement location than Europa.

Titan needs more study but will probably pass planetary protection eventually, as there haven't been any signs of cryovolcanoes there yet, which would be the only habitats Earth life could inhabit. In the other direction, we can't know for sure until we study it, but it seems likely that any Titan life would have a biology using fast chemical reactions that proceed so quickly at high temperatures that it it couldn't survive in an Earth habitat for long. 

If so, there are many advantages to its thick atmosphere, not least that you don't need spacesuits. You would just need a closed system air breather. There are other places you can do this too, for instance in the Saturn atmosphere, also some are enthusiastic for the idea of living in floating habitats at the Venus cloud tops where temperatures and pressures closely resemble Earth, if we can cope with the issues of the sulfuric acid (not so hard since you only need to make the outer skin acid resistant with teflon) and the lack of a solid surface. But Titan has advantages over both of those.

Even at those cold temperatures, it's practical to make gas filled thermal insulation that would work fine there and be not much different from what you would buy in a sports shop, though much thicker of course. Add an aqualung, or a more sophisticated closed system rebreather and electrical warming of gloves, and visor, and it is much easier to live there than almost anywhere else other than Earth (Venus would be the main contender if the cloud colonies are feasible).

It's got resources of ice, easily accessible, and the ethane / methane to use for making plastics, which are great also for 3D printers. 

It also has many sources of power, perhaps most notably the winds, which are only one or two miles an hour at ground level but reach 45 miles per hour at 40 km, which is fast enough to produce hundreds of megawatts of power from a wind turbine of diameter tens of meters mounted on a blimp in the thick dense methane atmosphere, and low gravity. And it's rather cool, humans could fly, and would survive a fall from any height with only minor injuries.  Perfect.

What's more it's a great base for the Saturn system, with methane already there as fuel, not for burning in the atmosphere, as it has no oxygen, but Elon Musk's BFR uses supercooled liquid methane and liquid oxygen. If you can extract oxygen from the ice, using those hundreds of megawatts of wind power, then you have a refueling depot for the BFR. With the low gravity it would be easy for residents to refuel their BFR, and take off and explore the Saturn rings, send robots to do flythroughs of the Enceladus plumes, control sterile cryobots as they descend into the Enceladus ocean, visit the Saturn storms and so on. Also they could explore Titan's seas in submarines and fly through its atmosphere in light planes. It would be as dark as a dark overcast sky all year round, possibly darker, with the thick atmosphere, and cold outside, but the Inuit manage Arctic winters fine. It would be the easiest place in our solar system to set up vast agricultural domes, covering square kilometers of the surface, filled with a breathable Earth atmosphere and with bright light from LED's powered by those wind generators. The atmosphere is transparent to infrared (and so to night vision goggles also), and indeed with the cold conditions there it might be a perfect place for constructing vast passively cooled infrared telescopes.

The atmosphere has no hurricanes or tornadoes, there are no earthquakes, winds at ground level are at most two miles an hour, and the thick atmosphere protects from cosmic radiation, solar storms, UV, and not just micrometeorites, but even rather large meteorite impacts,  There is no dust on the surface either unlike Mars or the Moon. And lots of hydrocarbons for making plastic.

Glint of sunlight on the lake region around the northern pole of Titan. Near infrared image. Titan could be a great place for a base for humans in the Saturn system. 

Anyway if you haven't checked it out yet, here is my recent article on Titan which got a fair bit of attention in social media. There's not much that's new there, it just summarizes recent research, which has become more interesting as a result of the prospects opened by Elon Musk's BFR and his image of it exploring the Saturn system. If he does succeed in producing it and keeping it low maintenance, and with low cost launches, this may be a prospect sooner than we thought.

Then this is about how in this vision we protect and preserve Earth. Amongst other things the lunar poles with liquid nitrogen temperatures are perfect for preserving seeds, viable for thousands of years. Mars has nothing like that. It could be a far better seed vault than the Norwegian one, and perhaps the nucleus for a small caretaker colony and eventually settlement based around preserving genetic diversity of Earth life in all forms in an off-planet backup.

This is about why paraterraforming, city domes, lunar caves and free space settlements are far easier to build, more economic in materials and also have far more potential for total settlement area than any planet, and how terraforming just isn't practical on timescales of centuries.

  • Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
    This is the insight that lead O'Neil and others in the 1970s to focus attention on free space colonies, rather than planets. It still applies today I think. Such habitats could be created rapidly using only in situ resources, and we could have the equivalent of a thousand planets in space in far less time than it would take to terraform Mars, if that is possible at all.

So, I'll take that background for granted here.

With this background, perhaps now we can return to the astrobiological issues for Mars. I'll present the astrobiological quandary. Then talk about the solutions the astrobiologists are exploring at present with two basic strategies:

"dirty robots" 


"science integrity and do as much as possible before the dirty humans get there" 

(where dirty just refers to the trillions of microbes that accompany us wherever we go, many of them able to live in extreme conditions, and we can't be sterilized of them like a robot)

Then I will also present what the situation looks like, and a possible third solution, with this much wider vision where the whole solar system is open to us and we are not just focused on Mars as the one planet that "has" to work for us

I will look at how with this approach of finding out what is on Mars, in a responsible way, respecting planetary protection measures where they are needed, we can end up with a win win win type situation. Astronauts would help explore Mars from orbit via telepresence, but as part of a much larger picture with astronauts in many locations in the solar system eventually. Robots and astronauts would each do what they can do best, working together, with robots going to situations either too hazardous and toxic for humans or ones where we can't yet predict the outcomes of biosphere collisions, or indeed, we can and the prediction is unfavourable.

In this vision Earth is our base which we protect and cherish. Many of our space activities are going to be to do with helping Earth. Putting mining activities off planet, solar power from space, Earth observation and satellites, searching for asteroids and comets, and mining them, or deflecting them if necessary, if there is an eventual chance of hitting Earth.

In this vision the Moon plays a central role as it is so close to Earth. We don't think of the solar system as separate planets but as almost like one super-organism, and seen like that, then the Moon is a central point close to Earth, but with a small gravity well, potential for spinning tethers to make leaving and landing even easier - and bound to be one of the busiest places in the solar system and a hub of activity once we start to spread further afield. It's also likely to be a hub for asteroid defense (if it is needed) , asteroid detection, and radio telescopes, infrared, optical and other parts of the spectrum looking out into the galaxy.

Surprisingly it's an astrobiological hub too. Its polar ices especially must have collected meteorites from all the stages of Earth's history. Not only from Earth though. Meteorites from Mars and perhaps even Venus, right back to the early times billions of years ago. Ancient meteorites from the shallow ocean beds of those primeval seas, and if we are lucky, some at least have organics preserved all that time at cryogenic temperatures of liquid nitrogen or lower. Who knows what astrobiological discoveries we may make on the Moon if there ever was life on those various bodies? We certainly should learn a lot about the early Earth.

(This is a somewhat shorter version of the Op Ed I just did: Let's Make Sure Astronauts Won't Extinguish Native Mars Life - Op Ed - I often respond to comments in Facebook by adding extra sections and sentences to clear up confusions or gaps, with much thanks to my Facebook commentators! Normally that works well, but this time it just wouldn't gel.  It got to the point where, though it's a good source of information, it is rather long and doesn't work well anymore as an article to sit and read through from start to finish. So I started again and rewrote it to a new plan, starting off by presenting the broader vision briefly, and also trimming some material in the rest of the article which though interesting, probably belongs in separate articles, e.g. about the Outer Space Treaty.)


I think almost anyone would be saddened if we had this headline news story in the 2030s:

  Astronauts from Elon Musk's new "Mars Port" have just found native life there. It was in a sample from a damp streak on a steep slope near the city. They added it to nutrients and saw small cells swimming before their eyes. They analysed the sample and found that there was no DNA present. There were no proteins either. Just RNA fragments. Sadly when they took another sample, they found DNA and proteins and evidence of Earth life. The life in their original sample has not survived, and so the video footage they took of those swimming cells is the only evidence we have that RNA world life ever was there.

Future Possible News : Mars Life Found Then Lost: Robert Walker:

Astronauts from Elon Musk's new "Mars Port" .have just found native life there. It was in a sample from a damp streak on a steep slope near the city. They added it to nutrients and saw small cells swimming before their eyes. They analysed the sample and found that there was no DNA present. There were no proteins either. Just RNA fragments.
Sadly when they took another sample, they found DNA and proteins and evidence of Earth life. The life in their original sample has not survived, and so the video footage they took of those swimming cells is the only evidence we have that RNA world life ever was there.

Made with this spoof news story generator

This story seems rather dramatic. Could this happen? Well modern life with its DNA, messenger RNA, polymerase, and a million different chemicals in every cell can't be the first form of life to evolve on our planet. So, there must have been earlier simpler forms of life. But they no longer survive. So the scenario of this story is something that could happen if our life encounters the same early forms of life on another planet as it did here.

Since astrobiologists hypothesized a shadow biosphere of RNA world life on Earth then it's possible that if Mars currently has some early life form of life, that after the introduction of Earth life, it survives as a shadow biosphere along with Earth life. But we haven't disccovered such a shadow biosphere anywhere on Earth. Wherever we look we find DNA based life. There aren't even any extreme conditions on Earth with alternative biochemistries. Hydroghermal vents, hot springs, the cold dry vallesy in Antarctica, every habitat on Earth is occupied by DNA based life. We also have many lifeforms here that are projected to be able to survive find on Mars too in the habitats there if they exist, so it seems likely that Earth life could spread to most or all of the projected Mars habitats too.

Of course it could continue to survive in some habitat that Earth life can't coloniz. Perhaps it tolerates higher salinity or lower temperatures or more hydrogen peroxide in the brines. However, by analogy with Earth's example it seems reasonably likely that DNA based life would take over from any earlier form of life at least in all the habitats on Mars that Earth life is capable of colonizing.

This sort of thing doesn't happen on Earth because all life here is DNA based. We have never found out what happens when two biospheres on different planets collide.

So then, why is this interesting?

The interior of a cell is so complex, a million complex chemicals in an intricate dance, that to a microbiologist it resembles all the creatures in the web of life of an ecosystem. It's as if the only ecosystem you ever knew was the African savannah - every cell has a savannah landscape inside with its grass, lions and antelopes - and for the first time you find one that has a coral reef inside, with algae, fish, corals and octopuses. It could be as amazing as that to discover an extraterrestrial microbe based on a different biology.

They could be revolutionary in more prosaic ways too. For instance enzymes from microbes adapted to extreme cold are the basis for detergents that let you clean things just as thoroughly with cold water as you did previously with hot water, saving on power, and reducing CO2 emissions. Those enzymes form a $1 billion industry.

We have no way to make a functioning living cell that has no DNA in it or proteins. Nor can we make any other form of life simpler than our complex DNA based cells. Yet, just that could be sitting on Mars right now.

So, is there life on Mars? And can Earth life live in its habitats (not necessarily the same thing)?


Most astrobiologists would have said this was not much of an issue as recently as a decade ago, as the surface of Mars appeared to be totally sterile to Earth life. But it's been an exciting last decade for present day Mars habitability studies.

This started to change around 2008 when Phoenix first found what appeared to be droplets of a liquid forming on its legs. They are now thought to be salty brines, formed where salts meet with ice, both thrown up onto the legs as Phoenix landed. Sadly, there was no way for Phoenix to analyse the droplets themselves, but the salts would be likely to be a mixture of perchlorates and sulfates rather than the chlorides and sulfides most common on Earth.

It also made isotopic measurements of the atmosphere which showed that planet-wide Mars must have a fair bit of water that is able to exchange oxygen atoms with the CO2. It couldn't tell if this happens continuously or episodically. However, since then we have many ideas for present day salty brines on Mars, close to the surface, as well as some indirect evidence. They tend to be hidden up to a few centimeters below the surface, close to the permafrost level in the regolith, and consist of only a thin film only millimeters thick or less, or droplets of brine - but "for a bacteria, that would be a huge swimming pool " as Nilton Renno put it (who runs the Curiosity REMS weather station on Mars).

Nilton Renno found that liquid water can form very quickly on salt / ice interfaces. Within a few tens of minutes in Mars simulation experiments. This is striking as it could open large areas of Mars up as potential sites for microhabitats that life could exploit. The professor says

"If we have ice, and then the salt on top of the ice, in a few tens of minutes liquid water forms. Our measurements clearly indicate that. And it's really a proof that liquid water forms at the conditions of the Phoenix landing site when this salt is in contact with the ice.

"Based on the results of our experiment, we expect this soft ice that can liquefy perhaps a few days per year, perhaps a few hours a day, almost anywhere on Mars. So going from mid latitudes all the way to the polar regions.

" This is a small amount of liquid water. But for a bacteria, that would be a huge swimming pool - a little droplet of water is a huge amount of water for a bacteria. So, a small amount of water is enough for you to be able to create conditions for Mars to be habitable today'. And we believe this is possible in the shallow subsurface, and even the surface of the Mars polar region for a few hours per day during the spring."

(transcript from 1:48 onwards)

That's Nilton Renno, who lead the team of researchers. See also Martian salts must touch ice to make liquid water, study shows . He is a mainstream researcher in the field - a distinguished professor of atmospheric, oceanic and space sciences at Michigan University. For instance, amongst many honours, he received the 2013 NASA Group Achievement Award as member of the Curiosity Rover " for exceptional achievement defining the REMS scientific goals and requirements, developing the instrument suite and investigation, and operating REMS successfully on Mars" and has written many papers on topics such as possible habitats on the present day Mars surface.

Some, or even perhaps many of these potential habitats are likely to be too cold, or too salty at least for Earth life to survive easily, or at all. There, the saltiness is a hard limit, as Earth life can't survive with a water activity level below 60%. It is a softer limit for temperature as some microbes metabolize and possibly even reproduction at very low temperatures, the limit of -20 °C used for freezers may not be a hard one if you are interested in life with very long lifetimes, too long to spoil your food. These microbes are hard to study as they often take months to revive to normal activity as you warm them up.

Depending on the mix of salts some of the liquid brines may be stable in the low (laboratory vacuum) atmospheric pressure of Mars, deliquescing in the night time humidity and drying out in day time or even stable through the day too. Some of these may be habitable "as is". Others may be too cold or too salty for any known Earth life "as is" but could be habitable by life that modifies its environment by forming biofilms (a suggestion by Nilton Renno). I'm not sure if it is what he had in mind, but it suggests to me the idea of biofilms formed by Mars life, which if it has slightly different biochemistry perhaps can live in colder conditions, maybe also saltier conditions than Earth life can tolerate. Might those make the brines more habitable for Earth microbes too?

Astrobiologists have a wide range of views on the habitability of present day Mars to Earth life. Some would still venture a guess that it is uninhabitable, but others have views somewhere between possible and likely.

If there is life, it is likely to consist mainly of microbes simply because in such harsh conditions on Earth it's microbial except possibly a few lichens huddling from the UV in cracks in rocks. And as we'll see later in this article the scenario in the story could go either direction, or indeed, some Mars life could make some Earth life extinct and vice versa. Another possibility is that similar but not identical chemicals playing a role similar to BMAA get misincorporated into each other's chemistry causing each biosphere to degrade the other one. In that case the creatures of both biospheres become sickly, and have neuro-degenerative diseases, etc. and both biospheres degrade each other as they mix, until eventually the creatures evolve to be mutually compatible. Another way it could happen is if clashing biospheres produce mutually toxic chemical byproducts, or the chemicals used in the biology of the cells themselves are mutually toxic.


I'd say this is a new development in only the last two or three years.Most of those writing on this subject today seem to take as a given that humans are going to introduce Earth microbes to Mars. This is quite a change from, say, a decade ago, when Chris McKay for one had ideas for biologically reversible human exploration of Mars. He thought that if necessary we could sterilize the site after a human landing by simply throwing the dust in the air to get the UV light to sterilize it.

What has changed is first, that some Earth microbes have turned out to be far more resistant to UV than previously thought, able to withstand hours or more before dying and some cyanobacteria can survive and even metabolize indefinitely in partial shade using natural pigments to protect themselves (experiments by DLR in Germany).

Then the ionizing radiation is less hazardous than thought, even for slowly metabolizing surface life in cold conditions. The average levels detected by Curiosity are only as high as the interior of the ISS and we also now know of many microbes able to repair their DNA within hours. Remarkably, they are able even to repair double breaks in the DNA using other intact copies of the same strand. It's now projected that radioresistant Earth microbes could withstand complete dormancy up to many thousands of years right on the surface of Mars, though not for millions of years.

Then Mars is globally connected via the dust storms, and the iron oxides in the dust are good at shielding spores in the dust from UV. It also seems to have so many potential habitats now. Scattered throughout the planet, and even many in drier, ice free, equatorial regions. None are confirmed but that's mainly because we need to send landers to visit them. There's a possible damp streak within kilometers of Curiosity right now, but mission planners have decided it can't approach closely to check it out because Curiosity is not adequately sterilized for this. After a human landing on Mars with their trillions of microbial spores, how can you ever be sure after that, that a sample you collect from a surface habitat is of native Martian life?

It's probably not a problem yet. There are sure to be a few remaining hardy Earth microbes on Mars already on our Mars rovers. They were sterilized to a high standard on launch, and more so by the conditions on the journey out there, but they didn't aimed for 100% sterility for practical reasons; it was just too hard to do with the technology they had.

However, the conditions there are harsh, and most think our microbes are dormant, just sitting there doing nothing, and that we haven't irreversibly introduced Earth microbes to Mars yet. Astrobiologists think that the planet is probably, so far, still in a state where we can explore it and find out about the native Mars biology, whatever it is, without the signal of Earth microbes confusing our searches.

The main differences that make a human mission such a quandary for astrobiology are:

  • Sheer number of microbes, trillions rather than thousands in a human spaceship
  • Spores are often airborne when released rather than stuck on the surfaces of the rover, and can fall into dust in shadows (so protected from UV)
  • Leaks from airlocks and spacesuits are unavoidable. Air leaks from the joints of a spacesuit wherever you go and at least a small amount of air from within the habitat would be also released at the start and end of every EVA. This would make it more and more likely that the spores spread through the planet
  • Impossibility of containing microbes after a crash of a human spaceship on Mars. The exteriors of human spaceships and spacesuits can perhaps be sterilized to some extent. The interiors, never.

After even a short stay in an Antarctic base the number of microbial spores in the soil around a human camp site for astrobiological researchers is staggering - they normally operate a "corral system" to keep it within the camp site. This could work for a while on Mars too, and after a rover mission across the surface, the life would be mainly localized to rover tracks and sites where they stopped (as shown in a humvee expedition through the Arctic). It is not likely to travel further than meters right away. So you could do relatively clean studies during your first human expeditions away from a base there. But this is only temporary, with many spores left in the dust wherever they stopped or did an EVA, that would start to spread further afield in the next Martian dust storm.

This is why astrobiologists have started to think of the time between now and the first astronauts on Mars as their only opportunity, or at least, their best opportunity, to find out about native martian life in its natural state, if there is any current (extant) life there.


The astrobiologists Alberto Fairén and Dirk Schulze-Makuch aim to try to speed up the process of searching for life on Mars by relaxing the measures used to protect Mars from Earth life carried there on rovers. That may seem rather paradoxical, but they have argued, in the article "Searching for Life on Mars Before It Is Too Late" that after the first human landing on the planet, it will soon be irreversibly contaminated by Earth microbes.

(N.B. "contaminated" here is not meant pejoratively. It's a technical term from space law. Article XI in the Outer Space Treaty, the legal foundation for planetary protection measures, uses the phrase "harmful contamination", and this is the standard term used for this in planetary protection discussions).

He argues that if we don't relax requirements now, we won't be able to search for native life on Mars at all before it is too late, saying: 

"It is very likely that our children or grandchildren (the Mars generation) will see astronaut footprints on the red sands of Mars, and at that moment, it will be much too late to straightforwardly identify the nature of true indigenous martians."

So, for instance they wish to send Curiosity to investigate a possible wet streak close to where it is exploring, right now, before it is too late to study such streaks in their original state. They know that it is not sterilized enough, and might introduce Earth life to the streak, if it is habitable. However, they say that we don't have much time left to explore such places before it's too late - because after the first astronaut footprints in the Mars dust there will be Earth microbes already spreading throughout Mars.

The problem here is that our modern landers are not as easy to sterilize by baking them in an oven like the two Viking landers because modern instruments tend to be more heat sensitive than they were back then. This will make it more expensive, and by the time we have done it, they think our window of opportunity for studying the life will be over. Much of their paper is devoted to a discussion of ways to distinguish between habitats that are colonized by introduced Earth life from ones that still have only Mars life in them.


The previous planetary protection officer Cassie Conley and the one before her, Jim Rummel, have strongly criticized this approach. They say that the proposed "dirty robots" would be as much of a problem as "dirty humans". They don't think the proposed methods to distinguish Earth from Mars life using genetic tests will be reliable.

They raise the point that we have had plans for humans to Mars as a near future mission for decades now, with nothing happening, and that the private spaceflight plans are "more hopeful than convincing", and that the future of both astrobiology and human missions depends on doing good science right now. They argue that there is still time to explore Mars properly before humans get there, and that it helps nobody to relax the requirements before we know what is there, saying:

A human mission to Mars is NASA's stated “horizon goal,” but this is not the same as a serious programmatic commitment—with an accepted rationale, budget, and schedule. To date, no government agency has produced such a commitment, and the details of private initiatives are still more hopeful than convincing. There is still time to explore Mars properly.

Their response is in their article "Four Fallacies and an Oversight: Searching for Mars Life,". The two papers are summarized in Debate Over Mars Exploration Strategy Heats Up in Astrobiology Journal, and both are open to read free online. I will discuss some of the other points made in these papers in more detail later on, so those short summaries just touch on some of the points they make.

Both are agreed on the central point however, that humans will introduce Earth microbes irreversibly to Mars, and that our best opportunity for studying any native life on Mars occurs before our Earth microbes are introduced to the planet. They differ in their views on how soon this may happen with the planetary protection officers suggesting it won't be for some time and that we have time to explore Mars properly.


Cassie Conley has just been succeeded by Lisa Pratt as NASA's new planetary protection officer. The few statements she has made in her interviews with the press are already being interpreted as suggesting she is open to relaxing the rules for planetary protection, perhaps along the lines of permitting "dirty robots".

As reported in ScienceMag

How do we designate a few, a very small number, but a few special places on Mars [where] we can get in now with rovers and landers and do a better job asking and addressing questions of—is there present-day near-surface life on Mars? We can’t just declare every interesting place off the table. Because that means the first time we’ll know anything is when we’ve got humans there.”

That "We can’t just declare every interesting place off the table" does sound a bit like a suggestion for "dirty robots" .

However, John Rummel, a previous planetary protection officer, before Cassie Conley and then Lisa Pratt says

“I would advocate for noncontamination of special regions, of course,”

“She is pretty careful, but still new to the job,”

Alberto Fairén, author of the "dirty robots" paper interprets what she said as supporting his proposal.

Lisa Pratt's main point is that she wants to do it in a way that means that they assist missions from the private sector, and don't look like some kind of a sheriff's department constantly coming down on them.

...But the office will also develop modern techniques for assessing microbial burdens, and it will seek a less confrontational relationship with the NASA centers, Pratt added. “We have to do it in a way that we assist the missions and don’t look like we’re some kind of sheriff’s department that is constantly coming down.”

NASA planetary protection officer suggests loosening limits on exploring Mars for life

I think as Jim Rummel said, she is new to her job and it's far too soon to say what difference that might make, if any.


One point she made, which astonished me, is that SpaceX didn't file a protection plan for the cherry red Tesla Roadster. As reported in SpaceNews:

“We were supporting their launch, but we did not have a planetary protection plan in place.”

... “What we do, and what ESA is doing, in some cases are requirements that would be virtually impossible for a commercial mission to meet,” she said. “We have to figure out how to work closely, how to move forward in a collaborative posture so we don’t have another red Roadster up there in orbit.”

Now, as it happens, it was followed for a long time by astronomers and they could determine a precise orbit. It's hance of hitting Earth in the next 3 million years of 11% and of hitting Mars minute. And by that time then it would probably be thoroughly sterilized by cosmic radiation.

The current rules for orbiters and flyby missions to Mars are that there has to be a chance of less than 1% of hitting Mars within 20 years and less than 5% of hitting it in 50 years. Now - whether those rules need to be changed is another thing, but that's not the job of the office.

Nearly all missions to Marshave upper stages that are in independent orbit around the sun like the Tesla. Here is an example, with the Mars Reconnaissance Orbiter, what they do is to deliberately point the upper stage a bit away from Mars and then remove that bias to get back on track, because the upper stage can't be sterilized.

So - there's nothing concerning about the Tesla Roaster as such in its current orbit. The only thing that makes it different from all those upper stages aimed to miss Mars is that he didn't file a planetary protection plan. It would be the same if he'd sent some lumps of concrete and barrels of water, or nothing at all, just the upper stage.

Was it just chance that he launched it at a time when there was no chance of it hitting Mars and at an inclination that made it impossible in the near future and highly unlikely long term? Or was that intentional?

So, I think her concern is not so much the Roadster, in the orbit it ended up in, but the precedent. And this just makes sense. It is astonishing to me that this wasn't done, that they weren't working closely with the planetary protection office to just run their plans past them and get their feedback and "okay", and indeed to have it on record for future scientists to refer to.


Cassie Conley used to say in her interviews that decisions like that, about what precautions we have to take to protect other planets and Earth, are above her paygrade. It's the same for Lisa Pratt or any planetary protection officer.

The guidelines on how to interpret this article are decided by an international group of astrobiologists through the COSPAR meetings, which are held every two years. She can't set the COSPAR policy herself. She would be there when the decisions are made and she might have some input into the conversations but she would not make that decision.

So she couldn't make any promises about relaxing the rules. That's for COSPAR workshops, or for Congress (for matters relating to how the international guidelines are applied in the US).


Laura Montgomery says that on her interpretation, only governmental entities are bound by the clause XI in the treaty about preventing "harmful contamination" and "adverse consequences to the environment of Earth". If private citizens choose to send a mission that will introduce microbes to Mars, or to return a sample that may cause harm to the environoment of Earth, then in her view, the OST only obligates the US government to tell the other States that this is about to happen, but not to intervene to stop it.

She thinks that on her reading of the Treaty, the application of this to private citizens in the US would have to be clarified by Congress.

Other lawyers disagree with her on her interpretation. For more about this see my: Does planetary protection law for individuals need to be clarified in the US?


 Her interview about her new job, posted on the Indiana University press release doesn't give answers. She talks about the question "Do we know enough about the possibility of present day life on Mars to safely take astronauts there?".

(click to watch on YouTube)

"It seems to me that the most important question we as humans could ever answer is, "Are we alone?" Do we know enough about the possibility of present day life on Mars to safely take astronauts there?

I have a burden, a burden of responsibility, to figure out how we collaborate with all the other nations and individuals who are capable of reaching Mars, to ensure that we understand what's there before we bring bits and pieces or intact spores of Earth organisms to Mars, and inadvertently inoculate a habitable planet.

During my time at IU (Indiana University) there are two things that I am most proud of. One is the recognition that there was a complex eco-system in these very, very deep, hot fluids in South Africa. But that then lead to the realization that Earth is unusually hot in the subsurface. And if we are interested in Mars. then Mars is a much colder planet. We then proposed similar work in deep mines in the Canadian Arctic. That was a real turning point for me, because that research was closely coupled to things that NASA wanted to know. That was the critical point when my career shifted to the exploration for life in places on Earth where people really hadn't done much looking.

The other thing I am most proud of is in the field campaign in Greenland right on the margin of the Greenland ice sheet.

I am so excited about the opportunity to be in the room when the decision-making conversations are taking place. To be actively participating in thinking about what are our rights and responsibilities at the moment in time when humans become space faring.

She raises the question of whether we know enough to safely take astronauts there. She didn't answer it, and all the COSPAR discussions so far on humans to Mars have concluded that we still have many knowledge gaps. So, at this stage anyway, she couldn't answer it.


This comes from other quotes from her on the Indiana University press release about her appointment:

"The importance of planning for the protection of Earth's biosphere, and for responsible exploration of Mars and other locations in our solar system, cannot be overemphasized,"

"With only a few decades left until there are boot prints on Mars, it is imperative for the international scientific community to plan for the unknown consequences of contact between two life forms and their biospheres. It's possible that 'first contact' has already occurred due to the unavoidable presence of spores and cell fragments on spacecraft launched from Earth and landed or crashed on Mars.

"If life does exist on Mars, which is a big 'if,' then we have a brief window of time remaining in which extraterrestrial life can be studied in near-isolation from terrestrial life,"

For me that is so sad, to hear her say that.

It is not a great surprise actually, as it's in other NASA announcements by the planetary protection officers in the past. It seems to be how they are thinking about the plans of either the government or the private space industry or both - that one way or another we will send humans to Mars in the near future. It's like a given, a fixed point in future history that they feel they have to work around.

Knowing what they now know about Mars, that Earth extremophiles can survive there, definitely as spores for thousands of years, and possibly also revive and colonize habitats there, spread in the occasional global dust storms - they conclude that it is inevitable that eventually we will irreversibly introduce Earth microbes to the planet. From that, it follows that we have only a brief moment of time to study Mars in its current uncontaminated state before humans get there.

Why this urgency? Why "only a brief window of time"? This is the question nobody seems to ask in this debate.


If we lose the opportunity to learn about Mars life, it is of our own doing. Nobody else and nothing else is imposing this on us. There are so many other places we can send humans in the solar system. Starting with the Moon, the moons of Mars, Venus clouds, Mercury, Jupiter's Callisto and beyond, including free space habitats too.

What is the urgency to land human boots on Mars as fast as possible? Can't we do both, send humans into space, learn about sustainable living on the Moon - and eventually send humans further afield. But on Mars, to study it from orbit, by telepresence, so that the astronauts there are part of the adventure of searching for life too.

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

They can speed up the robotic searches hugely by guiding them from orbit, secure in the knowledge that what they are doing does not in any way risk endangering the search for life there. And meanwhile we are finding out about Mars and placing various assets on the surface,which would be useful in the future if we do send humans right down to the surface. 

Also, if there is life there, we learn about its capabilities and its vulnerabilities before embarking on this hard to predict collision between the Earth and Mars biospheres. If there isn't life, we learn about the conditions on Mars and can begin to try to work out how Earth microbes would interact with them and what they would do to Mars (if anything).

If we do it this way, learn about Mars first, we can have a far better idea of what is there and maybe avoid future issues such as accidentally turning the water supplies on Mars to cement (more on this later). And if we find some vulnerable but incredibly interesting life there, then I think almost everyone will be on board with the need to protect it and study it carefully. And then we can develop proper planetary protection plans for this life, based on knowing what is there and what its capabilities and vulnerabilities are.

Is this "boots on Mars" and rapid colonization attempt what our children and grand children would want - if this is indeed the implication that we would lose the opportunity to find some wonderful discovery on Mars? Is it even what Elon Musk himself would want if that's the end result?

I write this article as a way to help get more public awareness of the perspective of astrobiologists and the planetary protection officers. Also to get us all thinking about it and talking about it.

The geologists and the colonization enthusiasts have their unique perspectives too, but there is so much more to space exploration than geology and colonization attempts. We need to get a complete picture on this if we are to avoid making maybe tragic mistakes as we explore the solar system. I think the more of us get involved in this debate, with all our various perspectives that we bring to it, the more likely that we can end up making wise decisions in the future.


So - now we get to the nitty gritty of the central problem that has dogged several COSPAR workshops on what provisions are needed for human missions to Mars. It's the issue the planetary protection officers constantly grapple with. We simply don't know enough.

Their reports come out with long lists of knowledge gaps. I don't see myself how they can be filled in a short timescale as the next decade, unless, of course, we had a vigorous astrobiological search on Mars right now.

It is such a large planet and the few missions so far have only just scratched the surface, and we have not yet sent a single modern astrobiology instrument to Mars or sent anything to search for life in the places we think present day life just may be possible. Indeed we haven't even looked for it properly where our current rovers are.

Curiosity could be driving over sand with dormant spores in it every day, and we simply wouldn't have a clue yet. It is not equipped with any instrument that could detect life. We do have several that could be sent, and a couple (UREY and the Life Marker Chip) got close to getting on a mission to Mars, UREY very close, until NASA pulled out of the joint mission with ESA which would have sent it to Mars - but astrobiologists have never yet managed to get any of their many instruments onto a mission to Mars. Not since the two Viking landers in the 1970s.

For more on this see


One example which for me shows strikingly that we just don't know what our microbes could do to Mars is the possibility of some early form of life there that's not yet evolved as far as DNA. We must have had such life on Earth, indeed quite possibly many different such life forms, independently evolved, but if so, it is now all gone (the idea of a shadow biosphere popular a decade ago doesn't seem to have panned out).

But this early life, now long gone on Earth, could still be there on Mars. It might be the only life there, or it might be there as a shadow biosphere of DNA based life (as was a hypothesis for Earth).

In either case it is potentially vulnerable to whatever made it extinct on Earth.

It doesn't have to be RNA world cells. It could be many things but one way or another, Earth must have had a simpler biology than our modern DNA based life. Everyone agrees on that, because modern life with its numerous intricate interconnections is just far too complex to arise in one go.

These early life forms are no longer here only because modern Earth life made them extinct. Again there is no other possible explanation, since modern Earth life survived and early life didn't.

Since modern life evolved from it, at some point there must have been both types present here, and then the earlier life was made extinct by modern life.

This proves that it is possible for modern microbial life from Earth, when introduced to another planet, to make life there extinct. Just as it did here when it made the early life here extinct. And not just a few species. It must be possible for modern Earth life to make an entire biosphere extinct so that there is not a trace of it left, only Earth life. Because that has already happened here on Earth with whatever was here before modern Earth life.


You may remember Bill Clinton's announcement of a discovery of life in the Martian meteorite ALH84001 - which was later retracted as not yet proven. Well even though we still don't know if it is life or not, it lead to a lot of interesting discussion and a workshop to try to figure out if such structures could be life.

Here are is one of their images from the original press release:

The structures in these photos are between 20 and 100 nm across, well below the resolution of a diffraction limited optical microscope of 200 nm.

These were tiny cell-like structures that some thought might be an early form of life because they were too small to contain all the biological "machinery" needed for modern DNA based life to reproduce. Although there is now an alternative geochemical explanation, it's an alternative, it's not a disproof that those structures are remains or fossils of life. Future discoveries on Mars could end up giving us the extra evidence needed to prove that they are life, if indeed they are.

The workshop convened on limits of size for cells showed in great detail that such small cells could indeed be life. Early pre-DNA life could be as small as tens of nm in diameter, like these cells.

So, they still could be life. They just weren't able to decide conclusively either way and the question remains open with opinions on both sides of the debate.

Now, of course they might not be life. The geophysical hypothesis may be correct. But whether they are or not, it does show the possibility that in the future we could find such structures in Mars meteorites, or on Mars itself, and this time be able to prove that they are indeed life.

Whether or not those cells are life, it does tell us something about ancient habitats on Mars as there is evidence that it was originally deposited in near surface warm water at 18 °C in ancient Mars.

This is normally given as a suggestion for past life on Mars, 4 billion years ago, the date for the Mars meteorite ALH84001. However, if we can find fossils like that, and if Mars is still habitable as some think, then it's at least a possibility that we can find present day life that is still like that on Mars.

That is, unless modern Earth life got to Mars long ago, and already made it extinct long before we came on the scene. Is this possible?


It's a major challenge for microbes to travel in the direction from Earth to Mars because of Earth's gravity and atmosphere. The rocks have to leave the atmosphere at the escape velocity of 11.2 km / sec. That's only possible for the debris of a large impactor, probably the likes of the Chicxulub impactor that hit Earth at the end of the dinosaur era, 66 million years ago. Also the rock has to leave Earth's surface at an even higher velocity, so has to be a blazing fireball all the way through the atmosphere. The shock levels as the rock is suddenly ejected from Earth by the impact are likely to be huge also.

Any life that did survive all this would have to be well within the rock where it was not burnt off by the fireball ablating its outer layers. In particular photosynthetic life is very unlikely to make it to Mars as it tends to live on the surface of rocks, or in cracks that would be reached by plasma from the fireball. And life that does get there is likely to just stay trapped inside its rock, landing on a dry cold dusty Mars with almost no atmosphere - unless this happened billions of years ago when Mars was more habitable. After surviving all that, then it also has to be sufficiently pre-adapted to the conditions there to thrive.

It's not impossible for a hardy microbe but it's no sure thing either.


It's also possible that there was some exchange of life, especially after the huge impacts over three billion years ago - and that whatever life got there plays nicely with whatever is on Mars, leaving the earlier life, whatever it is, as a shadow biosphere.

When astrobiologists design instruments to search for life on Mars they design them to be as general as possible. They reason that if they design them to look only for Earth life, they may miss out on the most exciting discovery possible, of life that is not like our form of life in some interesting way.

So, at least on the basis of what we know so far, there could be early life on Mars, either co-existing with DNA life as a shadow biosphere, or it may even have never encountered DNA.

Either way it would be vulnerable to whatever made it extinct here. So, based on what we know so far, it has to be possible that introduced Earth microbes make Mars life extinct.


Our experience studying microbes on Earth is not sufficient to test these ideas thoroughly. We do get invasive diatoms here as well, and they can prove a nuisance, for instance a diatom that is taking over fresh water lakes in New Zealand seems to have been introduced recently in the last decade or so on wet diving gear from the northern hemisphere. For more on this, with cites, see Invasive diatoms in Earth inland seas, lakes and rivers in my Touch Mars? book.

But this would be something over and above anything that is even possible on Earth. We simply don't have any examples of any life on Earth that would be as vulnerable to our microbes as some of the possibilities for what we could find on Mars. Nor can we make such forms of life in the laboratory.

The only life we can make is based on DNA, or small modifications such as adding two extra bases to the DNA base code (one of the most major accomplishments in recent years in this topic area - They added various features to their microbe including a "spell check" that let it hold onto the new bases for 60 generations which they think means it can hold onto them indefinitely).

There are plans eventually to replace DNA itself by the same code but using a different backbone, PNA perhaps. If so it would still be basically DNA based life doing all the same things, same cell processes, the same amino acids, RNA sequences and "language", but with PNA making up the genes instead of DNA. It would be nothing like as radical as a separately evolved or precursor lifeform. What we find on Mars could be wildly different, not even using the same basic building blocks. see Alien life could use an endless array of building blocks. We can imagine various possibilities, but as to actually building a test "RNA world cell", say, to see if it works, it is way beyond us.

It's not like putting lego pieces together to make a model - because the components are active, chemicals, doing things, reacting together, as soon as you put even two of them into the same place. It's more like trying to "herd cats" than to build something out of lego or Meccano.

(click to watch on YouTube)

EPS award winning "Cat Herders" commercial . Making a living cell from its chemical components, even if you know how it works, would be like herding cats. And we don't even know how an RNA world cell would work in detail.

Once we have a living cell we can make more just by letting it replicate, and we can modify it. But to make even the simplest cell from chemicals - no - that's way beyond us.

We can't use Earth bound analogies as a way to prove that it is safe to introduce Earth microbes to Mars. Because we have no proper Mars surrogate on Earth to test the ideas on.


This section is inevitably speculative. But we can't avoid that in this topic area. We may be about to go into a future that so far has only been the subject of science fiction stories.

So, there is another implication here too. If it's agreed that Earth microbes can make earlier forms of Earth life extinct, and so, potentially, Mars life too - what is to stop some even more advanced form of life making Earth life extinct? Not a super intelligence, I just mean a more evolved type of biology in every cell.

First, Mars life might well have no problems living on Earth. It's already adjusted to very oxygenated surface conditions with perchlorates and hydrogen peroxide, even though there is almost no oxygen in the air. It's also likely to be used to huge night / day swings in temperature, reaching temperatures well above O °C and sometimes 10 - 30 °C in summer in equatorial regions at midday and dry ice temperatures at night many nights of the year. You can hypothesize a form of life that is only able to survive in extremely cold conditions based on hydrogen peroxide and self destructs when it warms up. But it could also be as easily adapted to warm temperatures as Earth life.

Although you can make a good case for Mars life being less evolved than Earth life, you can also make a case in the other direction too. Mars has had many periods of variation in habitability. Some think that the "slush ball" or "snowball" Earth was what lead to the diversification of multi-cellular life in the Cambrian explosion. Well in that case Mars has had numerous potential "Cambrian explosions" in its brief periods of habitability. According to some ideas, for instance, early Mars was totally frozen over for hundreds of thousands of years. It's orbit varies in eccentricity over long periods of time, sometimes almost circular and sometimes very eccentric, leading to one or other of its hemispheres having exceptionally warm "summers. According to one of many theories about how early Mars was warm enough for liquid water oceans - at times when its orbit was particularly eccentric it becomes habitable every two years when closest to the sun. Other ideas include greenhouse gases, and they also may have had "snowball Mars" phases.

If it did happen this way, might all those "snowball Mars" phases have accelerated evolution? 

Also might there be variations anyway in the rate of evolution? Could Mars life have some feature that is as advanced over Earth life as the cell nucleus of eukaryotes is over prokaryotes? Or might it just have life with vastly more non redundant genes in their DNA (i.e. ignoring "junk DNA" and duplicated genes)? There has been a steady increase in the complexity of the genome of Earth creatures over billions of years, as measured in this way, and there is no particular reason to suppose this has stopped. 

So what happens when Earth life encounters another form of life with vastly more complex genomes than anything that has yet evolved on Earth? Equivalent to whatever will evolve on Earth a billion years from now perhaps?

Or could it be a mix, Mars life is more capable in some respects, and Earth life is more capable in other respects?

First a niggly nuisancy example. One likely adaptation for Mars life, faced with extreme cold, is that it can be more active in low temperatures than Earth microbes. This could mean we have to operate our freezers at temperatures lower than - 20 °C to prevent the food from getting spoiled by microbes that got transferred back to Earth from Mars or that have taken up Mars capabilities by lateral transfer (if Mars life also uses DNA).

For another more devastating concrete example, suppose Mars has a new form of life more capable at photosynthesis than any Earth algae in the sea or our land plants either? This is not implausible because with the low light conditions, frequent dust storms blotting out the sun, and the thin atmosphere, this might put efficient photosynthesis at a premium. For instance, our purple haloarchaea use mainly green light, and our plants and other algae use mainly the remaining red and blue light (reflecting away green light, the brightest part of the solar spectrum). Our seaweeds, in low light conditions, are often dark brown and some plants are black, using helper "antenna" pigments to get as much photosynthetic energy as possible.

Perhaps Mars life is also black and uses the full spectrum of all the light that falls on it?

We know that our plants have reached nowhere near the theoretical limit of efficiency for photosynthesis. Artificial enzyme paths have been designed using chemicals from many different lifeforms on Earth, mixed together in ways that they never could in nature, to make a form of photosynthesis that is 20% more efficient than Earth plants

"The end result was a synthetic CO2-fixing cycle, something which, as far as Erb is aware, "nobody has ever achieved before." A total of 17 different enzymes, including three "designer enzymes", are used from nine distinct organisms including human beings. The bottom line is that the CETCH cycle, where the Marburg-based researchers emulate photosynthesis's dark reaction, fixes CO2 at 20% greater efficiency than the Calvin cycle in plants."

That could be enough of an advantage to edge out Earth life. But if it uses some radically different principles, it might be far more effective than that. Earth photosynthetic life is only one percent efficient at converting sunlight to biomass. The Bionic leaf version 2.0 is able to convert 10% of the sunlight to biomass, using a catalyst made of cobalt and phosphorus with the help of a bacteria Ralstonia eutropha.

Also there is no reason for photosynthetic life to produce oxygen. Some consume hydrogen sulfide converting it to sulfur (CO2 + 2H2S = CH2O + H2O + 2S, the traditional photosynthetic equation with the O that enters into the reaction replaced by S).

More radically,the salt loving haloarchaea convert light directly into energy (through a proton gradient) much as the cells in our retina do, not producing any chemical byproducts at all. So, what if some Mars microbe is more efficient at converting light into biomass than our plants or algae but does not produce oxygen, and is inedible or poisonous to Earth life? It doesn't have to infect humans to be harmful.

It is also possible that unrelated Mars life is a pathogen of humans. It doesn't have to be adapted to us to do that. Take the example of Legionnaires disease, a disease of microbes and biofilms that uses essentially the same methods to live in human lungs. This shows that it is also possible that microbes evolved to infect biofilms on Mars could live in and on humans too, and if so, it's not impossible that it is harmful to us, accidentally. Often microbes evolve to become less harmful to their hosts rather than more so, as it is not in their interests to kill their hosts, and eventually, they may co-exist as symbionts.`

There are many other ways in which Mars life could be harmful to our astronauts or to Earth. For instance by producing toxins. Chrys Chyba gives the example of green algae in the Great Lakes in the US that produce toxins that kill dairy cows. They are of course not natural predators on cows; it's just an accidental poisoning. Well the same could happen with Mars microbes and humans.

The life need not use the same biochemistry to be hazardous in this way. It might indeed be a more likely issue for unrelated independently evolved life, which might produce chemicals that closely resemble amino acids, say, and confuse our biology.

How could that happen? For example if you eat a lot of sea food from fish that feed on algae blooms - in rare cases you can get a neuro-degenerative illness, Lou Gehrig's disease which causes progressive muscle weakness. It seems to be triggered by BMAA (produced by some algae blooms) which closely resembles the amino acid L-serine, and can get misincorporated into proteins in our body. An experimental treatment giving patients L-serine so that it substitutes back in place of the BMAA has shown some promise in tests.

It is rare for this to happen on Earth because it all uses the same biology based on a similar chemistry. But perhaps in a collision of biospheres, this sort of thing could be commonplace? Alien life may have many chemicals like BMAA that perhaps perform a similar role in their biology to chemicals that Earth life uses, but are not exactly the same and so mess up our biology when misincorporated.

Also perhaps there is a lot of accidental direct poisoning. For instance, oxygen on Earth may have made many earlier anaerobic lifeforms extinct or limited to niches within the larger habitats they used to occupy. For another example, if Mars life uses hydrogen peroxide and perchlorates inside its cells, in place of our chlorides, this could be accidentally toxic for most Earth life. The interior of our cells resemble droplets from a salty ocean, well the interior of Martian cells might resemble droplets of the liquids on Mars, which at present anyway are often hydrogen peroxide and chlorate rich brines. If it evolved in similar brines long ago, maybe that’s what it uses inside its cells.

For all we know,with our limited experience, it could even be the norm for colliding biospheres to mutually degrade each other until the lifeforms evolve and adapt to tolerate each other's biochemistry and work together.

For many more examples see Many microbes harmful to humans are not "keyed to their hosts" in Touch Mars?

Astrobiologists, when asked if Mars life could impact on our astronauts, or the biosphere of Earth, tend to say that they don’t know but think the risk is likely to be low. But not zero.

However I think it's important to realize that nothing like this has ever happened in our experience. We have nothing to compare it to.

In a way they are being asked the impossible. To assess it properly they would need to have experience of collisions of many different independently evolved biospheres, and we haven’t yet seen this even once. Or, of course, to have the opportunity to study Mars life first, before they answer the question.

We have to know the answers to this and many other questions, in my view, before we think about whether to go for a full scale biosphere collision between Earth and Mars.


As I write about these various ways that Mars life could be made extinct by our Earth microbes, I am reminded of a sad science fiction story that I use to help motivate my Touch Mars? book.

Few science fiction authors have tackled the theme of forward contamination of other parts of our solar system by Earth microbes, but there's one poignant sad story, by Arthur C. Clarke, "Before Eden". This story was published in the same year as his more famous classic short story "A Fall of Moondust", in Amazing Stories, June 1961. Back then, though they knew Venus was hot, scientists thought it was still possible that Venus could have water on its surface, perhaps at the top of its mountains.

One of the covers for Arthur C. Clarke's "Before Eden" -a poignant sad story about forward contamination of Venus, published in 1961 at a time when surface life there was still a remote scientific possibility. You can hear the complete story read as an audio book here.

These adventurers are exploring a completely dry Venus, or so they think. Up to then (in the story), everyone thought Venus had no water, and was sterile of life. That was a natural thought, because the temperatures they encountered were always above the boiling point of water. But the heroes of the story are stranded near the not quite so hot South pole, and find mountainous cliffs there. On those mountains they find a dried up waterfall - and then - a lake!

“Yet for all this, it was a miracle—the first free water that men had ever found on Venus. Hutchins was already on his knees, almost in an attitude of prayer. But he was only collecting drops of the precious liquid to examine through his pocket microscope.... He sealed a test tube and placed it in his collecting bag, as tenderly as any prospector who had just found a nugget laced with gold. It might be – it probably was – nothing more than plain water. But it might also be a universe of unknown, living creatures on the first stage of their billion-year journey to intelligence....”

“...What they were watching was a dark tide, a crawling carpet, sweeping slowly but inexorably toward them over the top of the ridge. The moment of sheer, unreasoning panic lasted, mercifully, no more than a few seconds. Garfield’s first terror began to fade as soon as he recognised its cause....”

“… But whatever this tide might be, it was moving too slowly to be a real danger, unless it cut off their line of retreat. Hutchins was staring at it intently through their only pair of binoculars; he was the biologist, and he was holding his ground. No point in making a fool of myself, thought Jerry, by running like a scalded cat, if it isn’t necessary. ‘For heaven’s sake,’ he said at last, when the moving carpet was only a hundred yards away and Hutchins had not uttered a word or stirred a muscle. ‘What is it?’ Hutchins slowly unfroze, like a statue coming to life. ‘Sorry,’ he said. ‘I’d forgotten all about you. It’s a plant, of course. At least, I suppose we’d better call it that.’ ‘But it’s moving! ’ ‘Why should that surprise you? So do terrestrial plants. Ever seen speeded-up movies of ivy in action?’ ‘That still stays in one place – it doesn’t crawl all over the landscape.’ ”

“‘Then what about the plankton plants of the sea? They can swim when they have to.’ Jerry gave up; in any case, the approaching wonder had robbed him of words... ”

“... ‘Let’s see how it reacts to light,’ said Hutchins. He switched on his chest lamp, and the green auroral glow was instantly banished by the flood of pure white radiance. Until Man had come to this planet, no white light had ever shone upon the surface of Venus, even by day. As in the seas of Earth, there was only a green twilight, deepening slowly to utter darkness. The transformation was so stunning that neither man could check a cry of astonishment. Gone in a flash was the deep, sombre black of the thickpiled velvet carpet at their feet. Instead, as far as their lights carried, lay a blazing pattern of glorious, vivid reds, laced with streaks of gold. No Persian prince could ever have commanded so opulent a tapestry from his weavers, yet this was the accidental product of biological forces. Indeed, until they had switched on their floods, these superb colours had not even existed, and they would vanish once more when the alien light of Earth ceased to conjure them into being...”

“...For the first time, as they relaxed inside their tiny plastic hemisphere, the true wonder and importance of the discovery forced itself upon their minds. This world around them was no longer the same; Venus was no longer dead – it had joined Earth and Mars. For life called to life, across the gulfs of space. Everything that grew or moved upon the face of any planet was a portent, a promise that Man was not alone in this universe of blazing suns and swirling nebulae. If as yet he had found no companions with whom he could speak, that was only to be expected, for the lightyears and the ages still stretched before him, waiting to be explored. Meanwhile, he must guard and cherish the life he found, whether it be upon Earth or Mars or Venus. So Graham Hutchins, the happiest biologist in the solar system, told himself as he helped Garfield collect their refuse and seal it into a plastic disposal bag. When they deflated the tent and started on the homeward journey, there was no sign of the creature they had been examining. That was just as well; they might have been tempted to linger for more experiments, and already it was getting uncomfortably close to their deadline. No matter; in a few months they would be back with a team of assistants, far more adequately equipped and with the eyes of the world upon them. Evolution had laboured for a billion years to make this meeting possible; it could wait a little longer.”

“...For a while nothing moved in the greenly glimmering, fog-bound landscape; it was deserted by man and crimson carpet alike. Then, flowing over the wind-carved hills, the creature reappeared. Or perhaps it was another of the same strange species; no one would ever know. It flowed past the little cairn of stones where Hutchins and Garfield had buried their wastes. And then it stopped. It was not puzzled, for it had no mind. But the chemical urges that drove it relentlessly over the polar plateau were crying: Here, here! Somewhere close at hand was the most precious of all the foods it needed – phosphorous, the element without which the spark of life could never ignite...”

" ... And then it feasted, on food more concentrated than any it had ever known. It absorbed the carbohydrates and the proteins and the phosphates, the nicotine from the cigarette ends, the cellulose from the paper cups and spoons. All these it broke down and assimilated into its strange body, without difficulty and without harm. Likewise it absorbed a whole microcosm of living creatures—the bacteria and viruses which, on an older planet, had evolved into a thousand deadly strains. Though only a very few could survive in this heat and this atmosphere, they were sufficient. As the carpet crawled back to the lake, it carried contagion to all its world. Even as the Morning Star set its course for her distant home, Venus was dying. The films and photographs and specimens that Hutchins was carrying in triumph were more precious even than he knew. They were the only record that would ever exist of life’s third attempt to gain a foothold in the solar system. Beneath the clouds of Venus, the story of Creation was ended.”

How sad it would be if future explorers on Mars get glimpses of early forms of life there, and then they go extinct soon after they are discovered. Or indeed, even before, maybe they are extinct before anyone finds them.

These astrobiologists, feeling that humans on Mars are inevitable and that there is nothing to do about it, are suggesting that we do what the science fiction explorers did in Arthur C. Clarke's book. However, they propose to do it, not by accident, but as a matter of policy. They envision Martian life inevitably getting taken over by Earth microbes or mixed with it inextricably, and propose exploring it in a way they know is not ideal for astrobiology, because it is the only way to get some good astrobiology done before it is too late.

This is tragic, in my view. And if there was more public awareness of the perspectives of astrobiologists, and the various insights from the planetary protection officers, and of the need for protection of Mars from Earth microbes, I don't think this would be necessary.


I do think the situation is slowly changing, Even in the last few years. Just a couple of years ago I'd say things like this and many people would respond, especially colonization enthusiasts: "Are you joking!" They thought it inconceivable that we'd send humans all the way to Mars orbit, orbit it and not land, just to protect native life on the planet.

But there is increasing awareness of these issues, and I hope that I and others who are blogging about it are helping to get this into public view, and to get this debated and aired widely before it is too late.

I find in discussions with the public, that there is a great deal of support for planetary protection and for valuing native ET microbes on Mars. They just have to have it explained to them carefully. 

It helps a lot that the message can be a positive one for human spaceflight, emphasizing the value of humans on the Moon and many other places in the solar system, including humans exploring Mars via telepresence - just not on the surface of Mars, or at least not quite yet.


Even if there are habitats there with no life at all, and no Earth life ever got to Mars, that also is amazingly interesting. What happens to a terrestrial planet with no life on it, but organics and habitability, after a billion years? 

Mars may be our only chance to study such a situation for many light years distance in any direction. If we blow this chance, we won't have the opportunity to study it again for generations into the future, not in this detail. Not even if we manage interstellar flybys of other planetary systems at some time in the future. The earliest we could expect to get data back even from a flyby of another star, never mind a robotic lander on one of its planets, is probably the end of this century. To study such a planet close up, to the detail we can do with our current robotic missions to Mars from Earth, is probably not something we can do for many centuries.

What happens on a habitable world with no life for billions of years? Do you get self replicating chemicals but no life? Structures that look like cells and maybe even have some kind of metabolism but don't replicate exactly? Giant organic crystals through Ostwald ripening? Nothing even slightly resembling life? This may be our only chance to find out. It could tell us a lot about what happened in the early pre-biotic stages before there was any life, but with millions of years worth of chemical reactions continuing beyond the conditions we can reproduce in laboratory experiments.

At least, it's our only chance until we can travel to other stars.

If there are habitats for Earth microbes at all on Mars, then that means there are habitats that our microbes will change. There will be things we could learn that will be lost by introducing Earth life there before we have an opportunity to study them. And until we know what is there, we simply have no way of knowing what we could lose.

Should we not find out what is there right now, before we decide whether it is okay to lose it?


If we make this decision to continue to protect Mars from forward contamination by Earth microbes and we find that we can't sterilize our spacecraft adequately to visit the special regions with potential habitats - or that the only way to do it is too expensive right now - well, we can wait until we do have the technology. Not just wait idly, but actively develop it. The Russians, drilling into the ice above Lake Vostok in Antarctica, stopped just a few meters short of the lake. They decided that it has probably been cut off from the surface for millions of years, so they just left it like that, while they decided what to do about the last few meters, and how they could do it without contaminating the lake with their drilling fluids and with microbes in the fluids.

Well it's similar with Mars. Do as the Russians did with lake Vostok. Not throw up our hands and say

"We don't have the technology, so, tough, we'll just rush in anyway and if we mess things up, so be it, at least we tried".

It would be so sad to do that, and then find that the native Mars life was made extinct by rushing, when a few more years of patience would have meant we could have learnt all about it.


Imagine how tragic it would be to have found direct evidence that there was life there up to just before we sent our rover? Or even, to detect it with a rover experiment but to observe the Earth microbes taking over the habitat before your eyes as you study it? This was the thought that lead to that "Fake Future News" story that opens this article.

Your first test finds some alien biology, e.g. DNA with an extra base, or a chemical in abundance, not usual in meteorites and not found in Earth life. Or with the example of an RNA world, even more striking, perhaps it only discovers RNA. cell walls and ribozymes (like ribosomes but much smaller, and made up of fragments of RNA). You find living cells, maybe you can even see them in an optical microscope swimming in the solution (there are proposals to send microscopes to help with the search for life even on robotic missions). You test and there is no DNA there at all, only RNA. Great excitement, you have discovered RNA world cells.

But as you repeat the experiments you begin to find DNA. Then more and more if it. The RNA world signal is getting weaker and weaker until all you can find is evidence of Earth based life in your sample. And the first sample with the exciting results - perhaps that's got contaminated too. Or just that you didn't provide quite the right conditions, they didn't like something in the nutrients you provided, and the life has all died. Most microbes even of Earth life can't be cultured in the laboratory, so it is even likely that it will be impossible to culture RNA world life when first discovered.

You would know for sure that there had been some form of Martian microbe there, you would know that it only had RNA and no DNA, but all you'd know about it is what little data you gathered before it went extinct in that habitat (and probably eventually Mars-wide, as the Earth life is transported in the dust storms). Then, much as for Arthur C. Clarke's scientists on his fictional Venus, the small amount of data you collected in your experiment would be the only evidence of extant RNA world life ever found.

As with Arthur C. Clarke's Venus explorers, those few photos, or maybe video of the microbes swimming would be far more precious than the scientists ever anticipated. They would be pored over by scientists for generations to come to try to glean more evidence and understanding of how the RNA world microbes worked. Those observations made by the first mission to find them might be all we ever learn about them as extant life rather than fossil remains on Mars.

And perhaps there are other square kilometers on Mars where the RNA world will survive for a while. Or maybe this is one of its last few refuges, as in the Venus story, and we don't find the other refuges until it is too late to study the lifeforms before they are extinct. Some of the potential habitats on Mars are very localized

How awful that would be.


The current planetary protection rules are that you have to have sterilization equivalent to that used for Viking on any spacecraft, or part of a spacecraft, that encounters a potential habitat on Mars.

This means a pre-launch bioload of 500 cultivable spores on the entire spacecraft and so about a hundred times that, around 50,000 spores or dormant microbes in total. That would be reduced further during the journey out and when landing on Mars, and through the surface conditions such as the UV. It's based on probabilities and the idea is to reduce the risk of contaminating Mars to a minimum.

But what if we have the technology to make 100% sterile rovers?

Well actually, it is possible, it's just more expensive. And not as a far future possibility with many engineering challenges to overcome. It is already possible to make 100% sterile landers in principle. We already have all the pieces in place; it's like a jigsaw puzzle ready to be assembled. There's a proposal for a 100% sterile cryobot that we can send to Europa for instance. That is by Brian Wilcox who is working on a 100% sterile probe to descend into the Europan ocean. It would have vacuum insulation like a thermos flask, a blade that cuts ice chips that the body then melts and analysed. It would be heated to over 900 °F (500 °C) during its cruise to Europa which would not only kills microbes but also decomposes organics that would confuse the results.

Vacuum insulated probe for Europa (screenshot from this YouTube video) - it doesn't heat the ice directly. Instead a blade at the tip cuts the ice into chips which the probe then melts and analyses. The probe would be heated to over 900 °F (500 °C) throughout the cruise out to Europa. It uses plutonium 238 for the melting - and so, presumably for its power source too, so there is no problem with batteries vulnerable to heating.

He describes it in a paper here (abstract, the paper itself is behind a paywall).

It's just the probe that's sterile here, not the lander. But combine that with ideas for a Venus lander and we may be getting close to a 100% sterile complete system.

As a result of research into high temperature components for use on Earth and for Venus too, we have all the components needed to build such a machine that is able to survive months of the voyage out to Europa at 500 C, so that the entire apparatus can be heated as a unit. No Earth life could survive that.

We could even remove the organics with CO2 snow. And a lot of progress has been made towards a rover that can drive over the Venus surface, again, in conditions that would sterilize Earth life. If we made it top priority I think our brilliant engineers could figure out a way to send 100% sterile rovers to Mars within a decade probably, if we already have one on the drawing board for Europa.

See also these sections in my online Touch Mars? book.

The first such rover is bound to be expensive to design, and test, and prove it works. But it would then give us the tools and experience we need to make any number of such rovers at far less cost. And then send them to any of the habitats on Mars, also with appropriate modifications, to explore Europa, Enceladus etc. What a huge difference it would make to have 100% sterile landers so that we don't need to be concerned about contaminating the places we visit with Earth microbes!

Once we develop the technology we will be able to use it to explore throughout the solar system anywhere we are searching for astrobiology. And we will be able to do that without any more concerns about whether microbes introduced on our instruments will impact on the potential habitats we are studying.

This was not possible in the 1970s when current planetary protection guidelines were drawn up. It was a case of either accept a percentage chance of contamination Mars, even if it was only 0.1% over the lifetime of the expected exploration period - or not to send our rovers there at all.

But now we do have a choice.


It seems possible that we haven't contaminated Mars yet, even likely that we haven't .For sure there are dormant microbes on our spacecraft but they are probably just that, most of them stuck in a crack, hidden from the UV and doing nothing.

However the aim for planetary protection measures for Mars so far has always been to reduce the probability of contaminating Mars. Certainty seemed unattainable and that wasn't the aim. So we should face the possibility, hopefully a very remote one, that, through blind chance, we have contaminated Mars already with Earth life.

If we have contaminated Mars already - suppose, heaven forbid, that the methane plumes were formed by microbes introduced to the Mars subsurface by one of the spacecraft that crashed on Mars or a microbe that somehow got into them? Well - hopefully not. But if they were - still, it's not a case of saying

"Okay we've had it, no point in protecting Mars"

That would be like saying "Okay we've introduced rabbits to Australia so it doesn't matter what else we introduce, wolves, foxes, plants, do what you like as it is already contaminated by rabbits".

That's not how it works. If we have introduced some microbe to Mars accidentally - well the native Mars life may still be there as a shadow biosphere. It may be possible to disentangle what happened and to still learn a lot. If that happened I think exobiologists would be very shocked. And everyone would want to know what happened, what we can do about it, and how to limit the damage.


One thing that would be great would be to get some in situ data on how effective our measures have been so far. We have been doing planetary protection for our missions to Mars for decades now, but it is all based on hypothesis and ideas, and tests in Earth conditions. We don't yet have a single point of hard data to validate those ideas.

If we are really serious about protecting Mars, I think as a priority we should send a mission to study one of the previous spacecraft we sent there, with astrobiology instruments to search for life.

This will serve several purposes

  • It lets us send astrobiology instruments to Mars, knowing that they will find something to study at least, the Earth microbial spores on the lander
  • Gives us our first data on how well our planetary protection measures have worked
  • Also can be combined with an astrobiology mission to study the region around the spacecraft. We may well find microhabitats there.

I would suggest sending it to study the Phoenix spacecraft. After all Phoenix observed what seemed to be droplets of liquid salty water on its legs, possibly Nilton Renno's droplets forming on salt / ice interfaces. These fell off the spacecraft onto the ground (or at least suddenly vanished from the leg).

Possible droplets on the legs of the Phoenix lander

Also Phoenix got crushed by the advancing dry ice in winter, as was expected for its location. It was never designed to last the winter as they knew it would get sheets of dry ice form on top of it and break it up.

Phoenix lander crushed by frost - layers of dry ice forming on the solar panel in winter snapped one of them off. It was not expected to last the winter. The right hand image shows it in 2010, two years after the image on the left which shows it after landing, in 2008.

If any of our landers have contaminated Mars, I'd have thought Phoenix was a likely candidate. As usual it was sterilized to high standards, but before Phoenix nobody realized there was any possibility of liquid there. Most of those potential micro habitats are probably either too salty or too cold, but are there any that Earth life could survive in? And are any of those close to where Phoenix lies on the Mars surface? We just don't know.


Jim Young (left) and Jack Farmerie (right) from Lockheed Martin, working on the Phoenix lander science deck under clean room conditions to protect Mars, following planetary protection guidelines. Credit: NASA /JPL/UA/Lockheed Martin.

However nobody back then knew that liquid water could form on the surface in those regions.

The entire polar regions of Mars are now declared a "Special Region" and all modern landers there will need Viking level sterilization for any part of the spacecraft that could potentially contact a microhabitat.

All of this is about as much of a battering any spacecraft there has had except for the crashed ones. We also know where it is exactly, we know we can land there, and we have its own observations of its landing site, which may be useful for comparison studies.

So, has it contaminated the ground around it? We will only have a few months to find out unless our rover can survive the dry ice sheets (which would be fascinating to study in situ). It is now thought to be an astrobiologically interesting region, so we can search for Mars life first at some distance from the lander, then approach it, and examine it for contamination by Earth microbes.

If we have a much more mobile lander, perhaps we can travel south from the Phoenix site as the winter dry ice approaches. It wouldn't be that hard to stay ahead of the advancing dry ice, and then return the next spring.

We could similarly visit the Viking sites, both to try duplicating the Viking experiments to understand what happened better, and to test the landers for planetary protection reasons. The Opportunity and Spirit rovers are both in sites of great interest for the search for past life, so an astrobiological past life mission could be combined with a visit to those rovers to check how effective our planetary protection protocols have been for them.

There's also the Mars Polar Lander crash site if we can find it.

The astrobiologists seem to think that there is a pretty decent chance we haven't contaminated Mars with Earth life, mainly because conditions are so hostile. Even if what we have on Mars is as vulnerable as RNA world cells, still, there is a good chance that it is still there and has not yet been extinguished by Earth microbes. And even in that case, we may be able to reverse what we have done, sterilize the rovers already there, or even remove them from the surface. We would need to develop those 100% sterile landers first of course, or we are just going to make things worse by trying to clear it up. But after that ...

We couldn't eliminate every single dormant spore from the dust. But most Earth microbes wouldn't be able to survive there anyway. Others would be sterilized by the UV, cold, heat, perchlorates or any of the other potentially biocidal factors on the Mars surface. We could go to the sites of crashed or crushed landers (via telepresence from orbit), and check to see if any life has started to spread. If so, it may be that it has not spread far yet and can be sterilized. It's not impossible that we are able to reverse the effects of what we have done so far.


As for the idea that it would be much faster to explore with humans - maybe - but at vastly greater expense and what good is it to be fast if you make what you are looking for extinct in the process?

The biggest bottleneck is not the roundtrip time, as you might think. Our rovers are so slow mainly because of lack of bandwidth at present. Our rovers could be as far away as Pluto or even a distant Kuiper Belt Object and it would make hardly any difference, because with the low bandwidth, they arrange for communications only once a day typically.

The US have one exciting mission in the near future, if it is approved - its Mars 2022 orbiter NeMO (Next Mars Orbiter) - a very important Mars orbiter to boost communications to and from Mars with "broadband" laser communication with Earth, as well as high resolution imagery of the surface at 30 cm resolution similar to the now aging HiRISE. This "broadband to Mars" could make a huge difference to future Mars exploration.

In the mid 2020s we'll have  800 gigabytes of information a day, a huge increase, if it goes ahead. We simply have no experience of exploring Mars with such a high bandwidth, and we don't even have this for the Moon. The Russian Lunakhod 2, using 1970s technology traveled as far in months as Opportunity did in years, and Lunakhod 3 (if it had flown) would have been faster still. But we have not tried exploring it with more modern technology for the rover, semiautonomous driving, high bandwidth communications, and the many advances in teleoperation technology.

So when bandwidth is our bottleneck, the first thing to do is to remove that bottleneck. We wouldn't send humans to Mars with the bandwidth we have at present. I think we will be amazed how fast the Moon, and then Mars, can be explored robotically once the technology is fully mature.

As an example, to show how it could potentially make a huge difference - for instance with multi-gigabyte 3D panoramas returned from Mars, and virtual reality technology you'd be able to look closely at any rocks around the rover with the equivalent of a geologist's hand lens just by moving around in the virtual 3d scene the rover returned to Earth. You could look closely at any rock, not by moving the rover, but just by walking up to it in 3D VR and looking at it in the images streamed back from the rover for that day. You could tell the rover to go around a rock and photograph it from all angles, and stream the images back, and within minutes you have a 3D image of that rock that you can zoom into with microscopic detail like examining it with a geologist's hand lens.

The rovers can easily be given vastly more powerful engines and more power for the experiments. Humans on Mars would not be driving around at 100 meters a day. They could explore at tens of kilometers a day like the lunar rovers, or even hundreds of kilometers, do Opportunity's entire journey in less than an hour if you so wished. The main reason we don't do that at present is that there is no incentive with the low bandwidth. If it takes days to do a photographic survey of just one small spot and send the images back to Earth - you get into a situation of diminishing returns by making the robot able to cover more ground, because you'd sacrifice instruments in order to add the capability.

Once we do that it also will be worthwhile to give them more autonomy like a self driving off road vehicle on Earth. For power sources - we can use fuel made from hydrogen feed stock on Mars as for the ideas for human driven rovers there, or we can use large areas of thin film solar panels spread on the surface to charge up batteries. Even the equivalent of the lunar rover batteries would give us plenty of mobility.

Eventually we can have humans in orbit around Mars which will speed it up yet again by adding our ability to make on the spot decisions within seconds. They will also be able to virtually "teleport" from one lander to another on the Mars surface, giving them tasks to do, much like directing the inhabitants in a game of Civilization.

And there is absolutely no urgent need to send humans to the Mars surface. The only thing the hopeful settlers have given as a compelling reason is that we need to be multi-planetary" to safeguard our species.

But if we want to make sure our species survives, we have to look after Earth. If we can't there is no way we can look after the much more harsh Mars. And it makes sense to have a backup in space, but as part of a situation where our priority is to protect and preserve Earth. If you think like that the natural place to do it is the Moon not Mars. And there are many other places we can send humans to in our solar system that don't have planetary protection issues.

I think we shouldn't change the rules to permit colonization enthusiasts to go to Mars as quickly as possible, to the one place in the inner solar system most vulnerable to Earth life.

If Elon Musk proposed to melt a hole into Lake Vostok, the subsurface lake in Antarctica, and drop a sub into it with humans on board and cruise around looking for hydrothermal vents, there would be outrage amongst scientists. They would dearly love to do that but they think it is very important to avoid contamination of the lake with surface microbes.

It would be even more so if he proposed to build a city of a million on the floor of lake Vostok. I think you can argue that a colony beneath the Antarctic ice, in a subglacial lake, would be more feasible in the near term than a city of a million on Mars.

If it matters even for lake Vostok cut off for only a few million years, of course it matters for Mars, and we should make that clear. That needs to be a starting point of planetary protection discussions, clearly and unambiguously recognizing the value of Mars for science, and the potential impact of Earth microbes on the planet.


We also have no idea what Earth life would do to Mars, in the unusual conditions there unlike any that we have on Earth - but possibly still habitable to Earth microbes. The previous planetary protection officer, the biologist Cassie Conley gave a simple example to show how we could get an unpleasant surprise if we introduce microbes inadvertently without knowing all the interactions and what they could do there.

Some Earth microbes, in the anoxic conditions on Mars and in the presence of methane (which may well be present there), could form calcite in underground aquifers - so turning them to cement.

"Conley also warns that water contaminated with Earth microbes could pose serious problems if astronauts ever establish a base on Mars. Most current plans call for expeditions that rely on indigenous resources to sustain astronauts and reduce the supplies they would need to haul from Earth."

"What if, for example, an advance mission carried certain types of bacteria known to create calcite when exposed to water? If such bacteria could survive on Mars, Conley says, future explorers prospecting for liquid water instead might find that underground aquifers have been turned into cement."

Going to Mars Could Mess Up the Hunt for Alien Life

In more detail, Mars has almost no oxygen, which changes how microbes behave. What she is talking about there is anaerobic oxidation of methane, which leads to the formation of calcium carbonate in anoxic conditions . It's done by a consortium of methane oxidising and sulfate reducing bacteria. See summary here in wikipedia: Calcite - formation process - which links to this technical paper which goes into more detail.

Calcite - calcium carbonate. In the anoxic conditions on Mars, in presence of methane, a combination of methane oxidizing and sulfate reducing microbes can cause calcite to form and so, basically, could turn underground aquifers on Mars into cement. Cassie Conley’s example of one way that accidentally introduced microbes could have unpredictable effects on Mars.

When it comes to microbes introduced to an unfamiliar planet that behaves differently from Earth, with many differences in the chemistry, atmosphere, environment - any number of unexpected interactions could happen.

Another thing that can happen is that the microbes from Earth mutate on Mars. That's likely in the unusual conditions, not like anything ever encountered on Earth, and the ionizing radiation will increase the mutation rate too; they can also recover hidden capabilities through changes in gene expression. They can also take up capabilities from Mars microorganisms via lateral gene transfer, if it is related, or is unrelated but still uses DNA / RNA. The resulting new pathogens combining traits from Earth and Mars organisms, or mutated in the Mars conditions, could endanger the astronauts too. Quoting from Conley and Rummel's paper

"Given the assumption that there really will be a serious effort to go to Mars with humans and have them do things on the surface, we can posit that human missions will inevitably bring a large population of Earth microbes along with them. We should anticipate, too, that not all of those microbes will always be harmless. If humans are going to contaminate Mars, we also need to be concerned about the possibility that the microbes they carry could endanger the astronauts, both in their native state and if they mutate in the space environment. If Earth life and martian life are related, or if martian life is unrelated but still uses DNA/RNA, then lateral gene transfer is another route for acquiring new (and potentially hazardous) traits. While COSPAR planetary protection policies are principally science-enabling, they have other benefits as well."

(Emphasis mine)

It's not as if Mars is the only place we can send humans to. We have the Moon, the moons of Mars, Venus, Mercury, and if Elon Musk is right about his BFR then within a decade or two we should have access also to Callisto in the Jupiter system and Titan in the Jupiter system to send humans to as well. Callisto has many advantages for humans over Europa as Elon Musk's ice refueling station in the Jupiter system and also for settlement - and is already passed as Category II, similar to the Moon, no problem sending humans there.

We can also build habitats in the asteroid belt, with enough materials there for radiation shielding for a thousand times the surface of Mars, slowly spinning the habitats for artificial gravity, or using two habitats tethered together lazily revolving around their center of gravity. They keep revolving due to angular momentum, and don't need any source of power to keep them going. It's like a bicycle wheel spinning endlessly on frictionless bearings.

Video fly through of a Stanford Torus style space habitat by Uzi Bento

In the future we could have humans fill the solar system right out to Pluto and beyond, and still keep Mars free from Earth microbes if we felt what is there is valuable enough and also vulnerable to Earth microbes.

With thin film mirrors you can get plenty of sunlight for a habitat even well beyond Pluto with much less mass than you need for the habitat to reflect the sunlight into the habitat.

For more on this:

Why the big rush to send them to Mars? Of all the places we could send them, why send them to Mars, one of the most vulnerable to contamination by Earth microbes? If we feel it urgent to ensure we have an extra "backup" in space, so urgent we have to do it right now, not wait even two decades, we can do it on the Moon, which has perfect conditions for a seed bank at liquid nitrogen temperatures in the craters of eternal night at the lunar poles, and can be developed into a small caretaker colony and eventually a larger settlement.

Also, for human exploration the Moon is close by, easy to get to (comparatively) but still a huge challenge that will stretch us to the limit. The Apollo astronauts made it seem easy, but it's not. They were test pilots that often made decisions in seconds that avoided disasters that would have killed everyone if they weren't experienced test pilots used to flying new designs of planes that could crash any moment, and often did.


You often hear this argument, which I think derives from Robert Zubrin, that it is no problem. The idea is that we will be able to tell if a species comes from Mars or Earth by gene sequencing. Either Earth and Mars life are related in which case we sequence them both - or else there is no DNA in the Mars life and that makes it even easier to know it is not Earth life.

Well to start with, gene sequencing is hardly trivial.

We'd like to test for life by putting dust into a nutrient solution and seeing if anything there metabolizes. For instance, if it only eats food of one symmetry and doesn't eat the mirror symmetry food (as is the case for all Earth life), that would be a good sign that we had found Mars life already, or some extraordinarily elaborate chemistry not present on Earth.

Or we look for amino acids all with the same symmetry. Or more dramatically, we might look at it with a microscope and see if there is anything swimming about in the solution.  There are many tests we can do, and some of them, or a combination of several, could establish beyond question, that there is native life on Mars, if not contaminated with Earth microbes.

But if Earth microbes have got there first, almost none of those tests will do. Even if we spot a microbe purposefully swimming around, flagella waving and undoubtedly alive, it will prove nothing. We have only one way to search for Mars life and that is, to look for DNA and sequence it, and test to see it is from Earth or not. We only know for sure if Mars life is present if there is no DNA there, or if the DNA is very different from Earth life.

Or we try to find some other chemical that may be produced by Mars life and not Earth originated. We are no longer looking for biosignatures, but we have to look specifically for "mars life signatures" before we can identify it as from Mars.

They make the DNA sequencing test 0sound easy. But even that is hardly a sure fire test. Of an estimated one trillion microbial species on Earth, only 100,000 have been classified, so only 0.00001% of all microbial species on Earth. Then 90% of those can't be cultivated in the lab, and are the result of sequencing a single isolated cell using new techniques which reached maturity around 2013. See Largest ever analysis of microbial data (May 2016).

From this you can see that if a microbe on Mars is not in our list of sequenced Earth microbes it tells us nothing about whether it is from Earth or Mars. There are entire branches of the tree of life, deeply branched, that are only known by a few fragments of DNA, with no cultivable species yet.

To complicate it further, microbes can swap DNA sequences via lateral transfer (using Gene Transfer Agents - GTAs) very readily, many of them overnight in sea water. This is a natural process that is so ancient that not only can a fungus transfer capabilities to an aphid, even the most distantly related microbes can exchange capabilities too.

If Martian life is based on DNA it can almost certainly transfer its capabilities to Earth microbes and acquire them too, in the same way. Before we have a chance to study what is there, we will have Earth microbes that have acquired Martian capabilities and vice versa. There will be no disentangling this mess to find out what happened, given that we don't even know which of the microbes there originated from Earth or Mars in the first place.

Alberto Fairén et al in their "Searching for Life on Mars Before It Is Too Late" suggest that though we couldn't necessarily distinguish individual Martian and Earth microbes,  at least, not if they are distant cousins, that we could distinguish a population of Earth microbes from a population of Mars microbes.

They say that we could do this for a few years after introducing Earth microbes there, as the generation times of Earth microbes on Mars are likely to be very slow, by analogy with behaviour in Antarctic conditions. It would take 50 years to cover a small patch of Mars of one square kilometer with a density of 5000 cells per gram. In detail:

"A more realistic example would be the generation time of 2.5 years for bacteria exposed to temporal freeze–thaw cycles in the permanent ice covers of Antarctic lakes. Assuming such an optimal environmental situation for Mars, a contamination of 100 metabolically active cells would require 50 years to produce a cell density of about 5000 cells/g in a square kilometer"

"Furthermore, we have an excellent control with which to monitor the potential contamination of Mars: sequencing the microbes found in the clean spacecraft assembly rooms. Any sequence identical or highly similar to those found on a martian sample would indicate very likely contamination and should be discarded as being indigenous to Mars.

"All the facts described above strongly suggest that if we ever find microorganisms on Mars, we will be knowledgeable enough to distinguish martian (exobiota) from terrestrial (contamination) life. That of course applies only for a short time span in the future, while the terrestrial biological contamination of Mars (if any) remains contained (close to our spacecraft) and known (present in our clean rooms) and therefore manageable. Human missions will change the name of that game forever."

Their idea is that we examine the habitats on Mars, sequence the genomes, and if the resulting population closely resembles the assemblies of microbe species from clean rooms on Earth, we discard it as contamination, and look again. In that way, they hope to be able to find the remaining genuine Martian populations that have not yet been contaminated by Earth microbes. They want to do this as quickly as possible before human missions make these studies impossible.

I find their reasoning a bit hard to follow here. Earlier in their paper, they suggest Curiosity approaches a potential habitat. But Curiosity is not equipped to detect life and certainly has no DNA sequencer on board, so there would be no way that it, for one, could distinguish between Martian life and Earth contamination. For that matter, it wouldn't be able to detect the Earth microbes either if they remained in small concentrations similar to those in other extreme conditions.

All Curiosity could do is to detect organics and it would not be able to tell if they came from Martian or Earth life or were just organics brought there from meteorites or comets. It's just not equipped for the job, being designed as a geology rather than an astrobiology explorer. There are many instruments we could send to Mars that are up to the task but none of them are on Curiosity (well except for one

Then, if we did send a more sophisticated rover with single cell gene sequencers - this is possible using SETG which is already space hardened and the experimenters say could be made ready to fly quickly - how do we tell if it is Earth life or our Martian cousins? They suggest testing to see if there is a deep branching from Earth life. But we often discover new forms of microbes on Earth that were separated from the other branches long ago. Perhaps some of those got to Mars in the past in which case it may belong to families we have on Earth already. But the Earth microbes that get to Mars on our rovers are also, many of them, going to be unstudied unsequenced microbes.

To complicate it all further, any Earth microbes that flourish in the Mars conditions are extremophiles and unusual. The conditions there are so unlike anywhere on Earth, with perchlorate, sulfate and hydrogen peroxide rich brine, battered with ionizing radiation, irradiated with strong UV (if there is any surface exposure), and with daily temperatures cycling through tens of degrees below zero and back to more habitable conditions. The salinity also goes through similar cycles every day. Though we have present day Mars habitability analogue environments that duplicate many of those conditions separately, - we don't really have anything quite like that in all respects on Earth. In particular we don't have the thin atmosphere (which is what leads to many of the other effects indirectly).  

Also, there are few places on Earth that are so super-oxygenated as the Mars surface with its hydrogen peroxides and perchlorates - which nevertheless also have significant chemical gradients if you just dig a little below the surface.

Any Earth life that can handle such strange conditions might seem quite alien if we haven't come across it yet in our studies here on Earth. Just the process of selecting the few Earth microbes able to survive in the habitat is likely to produce a community unlike any we have seen before, and could encourage many species of microbes to flourish that occur here in such low numbers they were never noticed  before.

As for their idea of sequencing microbes found in spaceship assembly clean rooms - no such census can be complete. Any of billions of species could get into the clean room and onto the rover, and it doesn't have to be one of the most common species that survives all the way to Mars and contaminates the surface. And the conditions in the clean rooms, though extreme, do not resemble the conditions the microbes encounter on Mars. There are many differences and so the populations of microbes that survive on Mars are just going to be ones that are in the intersection of microbes that survive the clean rooms and all the way to Mars with ones that can survive in the new habitats. Again it is possible that rare microbes, never detected in the surveys of the clean rooms, are the ones that proliferate on Mars.

Our microbes on Earth could also take up capabilities from any Martian life by lateral transfer and it could also evolve new capabilities, or unlock genes through gene expression that are rarely needed on Earth. The result could easily seem "Martian" and yet just be introduced Earth life. We might discover this, embarrassingly, months after announcing discovery of Martian life. Perhaps even years after the groundbreaking "discovery", someone spots this "Martian" DNA sequence on Earth in some new microbial survey and we discover that what we thought were new insights about Martian life were just insights into the behaviours of microbe stowaways adapting to the Martian conditions.

If you do somehow find a way to characterize the native Mars life - then so long as it is reasonably similar and DNA based, even as you study them, you are introducing Earth microbes, and these are sharing genes with the life you are studying via lateral transfer. Whatever information you collect during your mission will be the only information available to future scientists for all future generations about these habitats, as they were before you introduced Earth life to them. It is a philosophy of despair it seems to me.

And if the Earth life makes Mars life extinct, of course, then it doesn't matter how easily you can distinguish them.


However careful you are with the humans on the surface, however much you can slow down contamination (and everyone agrees it can only be slowed down - after a human landing then our contamination of Mars by Earth microbes is irreversible) - what can you do in the event of a crash landing?

The chance must be rather high. It's an exceptionally dangerous and risky mission for humans to attempt, requiring many complex steps to be done in a few minutes. After a Columbia style re-entry crash, debris would be spread over hundreds, or thousands of square kilometers of the Mars surface.

The debris field for Space Shuttle Columbia, with a debris track around 350 miles long, and about fifty to a hundred miles wide (depending on whether you measure to the most distant debris). An accident, especially if it happened early during the supersonic retropropulsion entry to the Mars atmosphere, could scatter debris over a large area of Mars.

If you send humans there, there is a chance that you are able to control the contamination to some extent and slow it down. But as Elon Musk himself says it is "fun but dangerous". Even with previous unmanned missions, there is still a high chance that the first human mission crashes there, so ending any possibility of even slowing down the inevitable irreversible contamination of Mars with Earth microbes. It's also unlikely that the precursor missions to set up habitats and fuel stations on Mars would be sterilized enough to protect Mars in the event of a crash.

If the human mission was to the vicinity of a region of interest for life, then the chance of contaminating that region even right away after a crash must be high.

So what can we do?

Well to start with, we are all of us together on this, as far as orbital missions around Mars and missions to the Mars moons, which would be likely to come first anyway for safety reasons. This may take a fair while.


The retired Canadian astronaut Chris Hadfield, former commander of the ISS, interviewed by New Scientist, put it like this in their article "We should live on the moon before a trip to Mars"

"I think ultimately we’ll be living on the moon for a generation before we get to Mars. If the world and the moon were threatened and the only way to preserve our species was to launch from Earth, we could go to Mars with yesterday’s technology, but we would probably kill just about everybody on the way."

"It’s as if you and I were in Paris, paddling around in the Seine in little canoes saying, 'We’ve got boats, we’ve got paddles, let’s go to Australia!' Australia? We can barely cross the English Channel. We’re sort of in that boat in space exploration right now. A journey to Mars is conceivable but it’s still a lot further away than most people think."

Elon Musk has big plans for his BFR. Perhaps that might change things, but on the other hand - we are at only the early stages of life support systems. The ISS has had numerous life support issues which were only fixed due to resupply from Earth. See this list of some of them. None were immediately dangerous, and some were relatively minor but some of them would have been fatal on a timescale of months.

The logistic figures support the idea that what we have now may be reliable enough for a Mars mission. It's hard to be sure though, with a sample size of 1. In a recent evaluation the conclusion is:

"With several readily apparent exceptions, WRS [water recovery system] and OGS [oxygen generation system] equipment has been shown to be capable of achieving operational lifetimes on the order of those needed to support such missions. It is important to note, however, that the sample size represented by the fleet of WRS and OGS ORUs (Orbital Replacement Units) that have been used in operational service remains very small (sample size of 1 in most cases) and that statistical reliability predictions cannot be supported by this data alone. Furthermore, other challenges likely to be faced in developing Mars transit and surface vehicles, such as mass and volume constraints, water and oxygen loop closure needed to support mission scenarios, dormancy management, equipment reparability, etc., also will need to be considered as part of an integrated Mars exploration mission and vehicle design. But in terms of highlighting first-order trends and focus areas needing improvements, the daily operation of the ISS WRS and OGS is providing an invaluable first step towards human Mars exploration. "

Even SpaceX do come up with a supremely reliable Mars capable spacecraft with the BFR, I think you would need to start with a "shake down" cruise in LEO testing the actual systems you would use for the mission for a similar duration mission in LEO with no resupply from Earth. Or for a more interesting mission perhaps -you can send it to the far side of the Moon, to L2. After all it is going to get no resupply from Earth during the entire mission to Mars. So, leave the BFR at the far side of the Moon, and they can explore the surface of the Moon via telepresence during their two years simulated Mars expedition. With Earth hidden behind the Moon it would have some resemblances to orbiting a distant planet. They could also introduce simulated radio time lag (which could be overridden in an emergency). Yet they can get back to Earth in a couple of days if something goes badly wrong.

So for practical reasons also Mars may be a step too far for humans. And when we go there eventually, we can have humans in orbit or on its moons, an exciting mission, to explore it via telepresence. All of that is compatible with planetary protection.

So we are together this far, all of us can be on the same page.

Indeed the BFR could make for an extremely spacious orbiting station for exploring Mars. As for gravity - the BFR could spin via a tether spin arrangement with a second BFR to generate artificial gravity throughout the journey to Mars and while in orbit around it. Tether technology is mature enough so that this is feasible no matter how slow the spin needs to be. The relative velocity of the two spinning craft would only be meters per second, not kilometers per second, so it is easy for them to dock with each other again in the case of a tether break, though you'd need to make sure the orbit was designed so that a tether break would not lead one of them to go careening into Mars.

If it had rather fewer people, 20 per BFR instead of 100, then his BFR could be spacious enough to grow sufficient crops to sustain the crew indefinitely, for years on end if necessary, providing nearly all their food and oxygen. Just inside the BFR, using solar collectors and light tubes for the light for the crops. I talk about this a bit more in my Value Of Titan As Base For Humans In Saturn System - Surprisingly - Once There - Easier For Settlement Than Mars Or The Moon

Once you can do that, you then open out the solar system. By sending a mission to orbit Mars without resupply for several years, and Venus also, those then would be "shake down cruises" to go further afield in multi-year voyages to Mercury, Jupiter and even further afield.

Perhaps, by then, we have managed to send astrobiological instruments to Mars - either before- or ones for them to use to study the planet from orbit with their first orbital missions there. If so, any of them could discover present day life on Mars at any time. As soon as that happens, the whole thing may begin to become much clearer to us all, as we begin to learn about Mars life, what its capabilities are, and vulnerabilities, and whether it is related to us.

I think the answer to Elon Musk's plans to send colonists to Mars is not to restrict ambitions but to be even more ambitious. Look further afield to Venus, Mercury, Jupiter, Saturn, eventually Triton, Pluto and beyond. But to keep Mars protected for now as part of an open future, with an initial phase of exploring Mars vigorously from orbit and using robots also operated from Earth. It's a case of being more ambitious, rather than less, and keeping our future options open, until we know more about what we are dealing with on Mars, which may or may not be compatible with us, if our biospheres collide. An affirmation:

"Yes, we can do this, we can explore Mars from orbit, and we don't need to introduce Earth microbes or risk getting our astronauts exposed to Mars life. We are in control of our own destiny and can decide what to do for ourselves. We are thinking beings and we can use foresight and insight to plan our futures".

There is so much we can do on the Moon. For that matter in many ways it is a far easier place to go, to do our first experiments in human settlement in the solar system than Mars.

  • No dust storms
  • the hard vacuum simplifies many things (e.g. can make solar panels by vacuum deposition in situ)
  • the dust is more easily managed in a windless environment and has nanophase pure iron mixed into it so that it can be sintered to glass easily with a microwave
  • sunlight 24/7 nearly year round at the poles
  • Double the sunlight levels of Mars
  • You can see Earth in the sky, nearly four times as wide as our Moon is from Earth.
  • large lunar caves that may be so big in the lunar gravity that you can fit a city inside, sheltered from solar storms, cosmic radiation and even fairly large meteorites too.
  • far more of an economic case, because it is so close and accessible compared to Mars, for tourism, and various suggestions for exports including potential for platinum from iron meteorite impacts, and ice at the poles
  • And it is huge too, continent sized, much to explore, much not yet known
  • Natural cryogenic conditions at the poles below liquid nitrogen temperatures, also suitable for superconductors and passively cooled infrared telescopes
  • Craters ideal for huge Arecibo style radio telescopes
  • Far side permanently shielded from radio interference from Earth

It is of interest to astrobiology too, because, just as we have Mars meteorites on Earth, the Moon must have them too. But not weathered, still in their original state. Not only that, in the cold traps at the lunar poles, meteorites will preserve organics not just from recent impacts on Mars but right back to meteorites that got here after huge impacts into the primordial Martian oceans. Any Mars meteorites from that time on Earth are long lost - the ones we have got here in the last few thousand years.

We may find meteorites from Venus too, possibly with traces of venusian microbes in them, if it ever had a thin enough atmosphere. Some think its present day thick atmosphere is only a few hundred million years old,and may have remained habitable to life on its surface until as recently as 715 million years ago. Its current atmosphere may have formed after a global upwelling of a vast magma superplume (something that can't happen on Earth because of the constant continental drift).

Also we can be certain that it will have meteorites from early Earth, after impacts here billions of years ago. They will be preserved there complete with the organics and DNA etc, kept at temperatures of liquid nitrogen and below for billions of years from right back to soon after life first started to appear on Earth.

Although it hasn't had a lot of attention, potentially the Moon might be as much of a treasure trove for the study of past life as Mars. Maybe more so in some ways, as it may take a fair bit of exploration on Mars before we find the places with the right conditions to preserve past life there for billions of years.

Phobos, the innermost moon of Mars is also expected to be a treasure trove of meteorites from early Mars. Without the cryogenic conditions, but meteorites preserved after a short flight path and in great abundance from the entire history of Mars, or at least, since Phobos formed.

I cover this in detail in these sections of my Touch Mars? book:

As humans we are not just the biosphere's way of getting into space. We are also our biosphere's "noosphere" (a term from Theillard de Chardin). We are our biosphere's way of thinking about the future and anticipating consequences and avoiding consequences that could be disastrous or unfortunate for it and for us. We can be its way of protecting itself from asteroid impacts too and anything else that threatens our Earth from space.

And - when we go to Mars, instead of working out what we are going to do to it, instead of doing our best to impose what I think can only be a pale copy of Earth's biosphere on it - we can instead find out what is there. Not be scared of the unknown. If Mars life for instance is not even based on DNA, maybe has perchlorates instead of salts and hydrogen peroxide inside its cells (one idea). Whatever it is, we aren't scared of it, we don't try to make it into something it isn't, we find out what it is first before we "do" anything to the life or the planet.

I think that is a far more interesting and adventurous way to proceed than to head out into the universe to try to make everything into copies of Earth as our top priority.

It is within our capability to ensure that we have more than a brief window of time, and that if necessary we can take as long as is required to find out what is on Mars and how Earth microbes will interact with it and how it will interact with Earth life and our astronauts, before sending anyone there.


Here he answers a question on this topic, in the 2015 AGU conference in San Francisco, 30 minutes into this video:

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

His answer:

A. "Well it really doesn't seem like there is any life on Mars, on the surface at least, we are not seeing any sign of that. If we do find some sign of it, then for sure we need to understand what it is and try to ensure that we don't extinguish it, that's important. But I think the reality is that there isn't any life on the surface of Mars. There may be microbial life deep underground, where it is shielded from radiation and the cold. So that's a possibility but in that case I think anything we do on the surface is really not going to have a big impact on the subterranean life."

So what would his reaction be if he thought there was a definite possibility that Earth microbes could make Mars life extinct and that such Mars life could be present on the Mars surface right now?


Mars is vast. Its  surface area is as large as all the continents of Earth put together.

It is difficult to visit also. Half the missions there have crashed. The US is not the only ones to go there. Indeed Russia made many attempts to land on Mars, none successful for more than a few moments. The UK sent the Huygens lander and it nearly succeeded but one of its solar panels failed to open, as we found out only years later from orbital photos and it never “phoned back”.

It is just a really hard planet to land on. Perhaps the US were lucky, maybe they had better technology. For whatever reason they are the only ones to succeed, and they too have had their share of crashes.

ESA’s Schiaperelli lander also crashed. And nobody else apart from those three, Russia, US and ESA have the technology yet to attempt a landing on Mars. With its thin atmosphere but high gravity (compared to the Moon), it’s the hardest place to land in the inner solar system.

So far we have had only these successful landers, all from the US:

  • Viking 1 and 2 - the first and only astrobiological missions. None of the others have attempted to search for life there. They produced ambiguous results that are discussed to this day -due to the bizarre and totally unexpected chemistry of the Martian soil interfering with the experiments. We now know the problem was that they are rich in perchlorates which are very unusual on Earth. They were stationary landers and the places they landed we now know to be not very habitable.
  • Pathfinder + mini rover Sojourner - a geology mission looking at rocks in one small patch of Mars, the “rock nest”.
  • Phoenix lander. Found evidence of water present on the surface in present day Mars both from droplets on its legs and isotope evidence in the atmosphere. This is now thought to be the only one of all these missions to have been sent to a region with a decent possibility of present day life - though that was not realized at the time. However it was not able to move and had no life detection capabilities.
  • Opportunity and Spirit - rovers. Spirit got stuck in the sand eventually. Opportunity is still running. It’s traveled over 10 km. Found salts, minerals that could only form in water, the "blueberries" that on Earth are the product of biological activity but we don't know on Mars, and many other things. But had no life detection instruments, past or present.
  • Curiosity - still exploring - got good evidence that Mars in the past had habitable lakes in Gale crater - and found organics probably from meteorites.

So - only seven rovers. The equivalent of one to each continent if you compare it to Earth.

Only two of those had the ability to detect life in low concentrations, Vikings 1 and 2 in the 1970s, and they got ambiguous results confused by the unexpected oxygen rich perchlorates in the dust.

Meanwhile our orbiters have found numerous possible sites to search for present day life.

None of these have been visited by either a lander or a rover.

Nor have we yet sent any spacecraft to the surface able to drill more than a small way into a rock. For past life we need to drill meters to have a decent chance of finding it (life on or near the surface has to be metabolizing - even if only slowly - in order to repair its DNA over time periods of thousands of years)..


There are many suggestions now for habitats not just at the base of the regolith, but on the surface or in the top cm or so of the soil as well. There is an almost bewildering variety of possible habitats for surface, near surface and subsurface life. None confirmed but many to be investigated. Here are some of them - the links take you to the section of my online Touch Mars? book.

On or near the surface, top few cms:

Habitats either close to surface or well below:
Well below the surface

Also see Modern Mars Habitability in Wikipedia (one of my contributions to the encyclopedia)

 None of these have been visited by either a lander or a rover.

The life in most of these habitats would be expected to be invisible from orbit. The lichens and cyanobacteria would be likely to be hard to detect from orbit too, as if they behave as they do in Antarctica they would huddle in partial shade in cracks in the rocks, and would probably do it even more so in the harsh UV of the Mars surface.


The surface radiation is sterilizing for microbes that are dormant for hundreds of thousands of years, which is not long enough for them to survive on the surface since last time it was warm enough for liquid water on the surface. That's why most astrobiologists, until recently, would say that any viable life on Mars has to be at least a few meters below the surface.

However, starting with Phoenix and the high resolution orbital images, we have found many possible ways that liquid water can form in the top few cms.

Some radioresistant microbes on Earth such as Chroococcidiopsis can repair damage from ionizing radiation within hours. Even double breaks right through the DNA strand, using other copies of the same strand to fix them - it's remarkable. They would have no trouble surviving in the conditions there even if metabolizing so slowly that the cells have individual lifetimes of millennia.

On shorter timescales the radiation is no problem at all. It's roughly equivalent to the radiation levels inside the ISS. Microbes can handle that no trouble at all, even humans can, with a slightly increased risk of cancer.


The damage is exponential and though nothing much happens over millennia, over millions or billions of years it is totally devastating. 
For instance, suppose that the number of viable microbes in a particular species is reduced to a tenth in 10,000 years. Well within 20,000 years you have only a hundredth of the original cells, after 30,000 years only a thousandth and so on. Within 100,000 years you have only 1 in 10 billion of the original cells surviving, within 200,000 it is only 1 in 100 billion billion or 1 in 1020 - and after a million years you can see there is essentially no chance of survival (1 chance in 10100 )

When it comes to drilling for past life, then over billions of years, the cells are not only killed, but most of the organics are decomposed to carbon dioxide, water, methane etc. For a reasonable signal of past life you need to drill deep, several meters. But most of the organics you find will still probably be degraded beyond recognition or not derived from life originally anyway. That's why the astrobiologists say it is so important to search for life in situ, so you can test in many different locations, at different depths. It is just impractical to return all those samples to Earth for testing here.

ExoMars will be the first to drill for life. For some reason NASA haven't been interested - though the Beagle also had a robotic mole so ESA / UK in that case have a long term interest. NASA are sending the InSight lander but although its heat flow probe will drill down for five meters, it won't be drilling to search for past or present day life.

Deep below the surface any present day life would be dormant, unless you are lucky enough to drill into a geological hot spot (none yet known on Mars). But it might be revivable and stay dormant for millions of years if you dig deep enough so that it is protected from surface cosmic radiation. 

So you have these two possibilities for present day life on Mars. It could be on or near the surface and able to repair its own DNA in hours, and so has no problem at all with the ionizing radiation. Or it could be several meters below the surface and has been there dormant, perhaps for millions of years, too deeply buried to be affected by the ionizing radiation on the surface.


There are plenty who do say it is possible that there's life there close to the surface of Mars in their papers. I summarize their views in the section "Views on the possibility of present day life on or near the surface" in the article Modern Mars Habitability

The main views I summarize there as (removed the footnotes):

  • Unlikely - these authors cite the inability of microbes to survive dormancy on the surface between periods when the atmosphere is thicker, due to ionizing radiation, the ephemeral nature of surface habitats, low temperatures, or low relative humidity, and the difficulty of colonization in surface conditions of high UV
  • Possible, recolonized from below, these point out the ability of micro-organisms to repair damage by ionizing radiation and capability to remain dormant for up to several million years in the deep subsurface, suggesting that these short lived surface habitats, such as the Recurring Slope Lineae, could be recolonized from the subsurface.
  • Possible, open question if it proliferates on the surface these are investigating the possibility with experiments in simulated Mars conditions, theoretical models and study of the observations from Mars, and treat it as an open question for now, whether the present day surface and near sub surface is habitable. .
  • Likely Some researchers, particularly the researchers at DLR consider that their experiments have already shown a high likelihood that the surface of Mars is habitable, for some lichens and cyanobacteria, taking advantage of the night time humidity, and even in equatorial regions such as Gale crater.[.
  • Already detected on the surface A small minority of authors believe that their reanalysis of the Viking Labeled Release experiments already indicates presence of life on present day Mars

There is greater agreement on deep subsurface habitats since conditions there may be similar to Earth conditions. They would be protected from UV, cosmic radiation, and the low pressure of the atmosphere, and water activity would be likely to be similar to Earth. For instance the deep hydrosphere (if it exists), or temporary lakes that form after impacts or volcanic eruptions, seem likely to be habitable, by analogy with similar habitats on Earth.


Many seem to think that any life deep below the surface would be immune to disturbance from the surface, as Elon Musk said in his quote. Perhaps some of it is. But Mars is a little different from Earth. Even here there's some contact. On Mars, many microbes in the deep hydrosphere or in geothermal hot spots and caves could still be vulnerable to spores scattered in the dust after a crash of a human occupied spacecraft on Mars.

One thing that makes this more likely is the way that the entire surface of Mars is "gardened" by meteorites on a planet with almost no atmosphere, ten times the meteorite flux of Earth, and no continental drift to recycle the surface and reform rocks. The ground is thought to be permeable to considerable depths over much of Mars. Even on Earth you get surface seeps from methane from deep subsurface reservoirs of gas.

Then, 90% of the rocks in the vicinity of Viking 2's landing consisted of porous basalt, riddled with holes. If there's some source of hydrogen, for instance, it could be very habitable. Basalt has has the chemical elements needed to support a million cells per gram (limiting factor is phosphorus) and there are likely to be perchlorates, nitrates and sulfates from the surface to increase its fertility for life. See this paper.

The methane plumes that Curiosity detected, if they are confirmed, may well be signs of some communication between the deep subsurface and the surface. If so, then that could mean there is possibility for transfer both ways. That might become not just possible, but likely, if some geothermal hot spot reaches to close to the surface and makes surface brines habitable (one hypothesis for the RSL's).


Part of it maybe is that scientists are more comfortable working with things they know are there rather than possibilities that can't be proved yet? Perhaps that's one of the main things I can bring with my background in maths and philosophy.

Absence of evidence of life on Mars is not in this case evidence of absence because we haven't looked, and we don't yet have any missions yet even on the drawing board to look at the locations where present day life may be on Mars. They can't be seen from orbit because most of the habitats are cryptic in the near vacuum Mars atmosphere - most are below a layer of dust or rock or salt or ice.

Life in such cold conditions may also be in sparse populations slowly metabolizing with individual microbe lifetimes which may even be measured in millennia (by analogy with some Antarctic populations) and have negligible effects on the atmosphere. Probably much or even all of it is not detectable even by the Trace Gas Orbiter, sensitive as it is.

And as we saw, the Mars 2020 sample caching followed by a later sample return (if that does go ahead) will not answer this question. It's not even designed to address it.


I think it's important to realize that a null result is important too. Indeed as we search for life on Mars we may get many null results, in one place after another, as we narrow down the search for life there.

If Curiosity had life detection capabilities, it could answer one question right away, "Did Viking find life or not in the 1970s?"

We have day / night rhythms when we sleep at night and eat during the day. Well microbes do too.

These are called circadian rhythms and these patterns were discovered many years later in the Viking labeled release data. The interesting thing is that they are offset from the temperature variations by two hours, which to an expert on circadian rhythms who spotted this, strongly suggested that these rhythms come from  life rather than non life processes. Ordinary chemistry can only explain an offset of about twenty minutes.

More on this in the section Rhythms from Martian sands - what if Viking detected life? in my online and kindle book Touch Mars? Europa? Enceladus? Or a tale of Missteps?

Suppose it comes up with the answer "No"? Then we have our answer to this question that has lead to so much debate for decade. It could also determine what chemistry was involved that caused these apparent circadian rhythms in the nutrients offset by from the temperature variations.

That is how you do science. If you are scared of null results, your progress is going to be very slow. Short of spotting an obvious fossil, or a large lichen or some such, we aren't going to find life on Mars until we send astrobiological instruments there to look for it. And then keep looking, until we have tried all the main proposed habitats, and several times over too. As astrobiology isn't neat like geology. The life can be cryptic, hidden inside rocks and beneath a layer of dust or salt, but it can also be very patchy in extreme environments. In the Atacama desert some gypsum pillars have life and some don't, as a result of just a small change of humidity. Similarly if there are cyanobacteria colonizing beneath the surface of rocks, some will have them, and drill just a centimeter to one side, even on the same rock, and you may miss it.

Most astrobiologists do not expect NASA's sample return mission, starting with Mars 2020, to find life. Eight of them warned in a forthright paper to the decadal survey that they expect it to return samples as ambiguous for their subject as the Mars meteorites we have already. It is likely to find organics, but if it returns those to Earth, there will be the same questions we have with the Mars meteorites we already have. Organics are constantly falling on Mars, brought there by comets and meteorites. It's actually more of a mystery why there aren't more organics there; these infalling organics seem to be destroyed rapidly by surface processes, and the organics found by Curiosity already are thought to be from meteorites.

I cover this in detail in my section: Astrobiologists advocating strongly for an in situ search on Mars first in the book. I go into the papers by  Bada et al', by Paige, and by Cockell et al, all arguing that we need an in situ search looking for biosignatures and life itself in situ before we even consider a sample return - at least if the reason to return the sample is for the purposes of astrobiology.


The geologists have their priorities but what about astrobiological missions? Some of the geological sites we have visited already would be great sites for a follow up astrobiological missions.

I think few of us realize quite how astonishingly varied and complex Mars has turned out to be. Perhaps by describing some of the places we can look for present day and past life on Mars, it can help to give an idea of the quandary the astrobiologists are in. They would like to explore all these habitats, but if humans land on Mars as soon as the 2030s then they probably won't have yet sent an astrobiological mission to any of them, at the current pace of progress, just more preliminary geological missions with some chance of spotting life if it is very abundant, which is unlikely in the places those rovers are likely to visit in the near future.

Here are some of the places where you would definitely want to search for present day life in situ

  • The walls of Valles Marineres to search for Recurrent Slope Lineae - on steep slopes so it needs a mission with a rover together with a second one lowered on a line down the slope - there are hydrated salts associated. The brines do not cause the darkening directly, which may be due to cascading dust, but the way they slowly extend through spring, then broaden and then fade in autumn, first appearing when local temperatures reach O °C only in sun facing slopes suggests there are likely to be thin layers of brine just below the surface that somehow trigger them. The hydrated salts back up this hypothesis. If so, either the brines, or whatever is the source for those brines, may be habitable. Only some slopes form them and we don't know why that is.

    There are many of these along the Valles Marineres and others at much higher latitudes.
  • RSLs at higher latitudes, with many of them now identified. Though they are visually identical, that doesn't have to mean that they all form in the same way, with the same source for the brines. If the brines are at least marginally habitable you'd want to follow this up with a visit several of each type as life may have got to some and not others or they may vary in their habitability depending on the local geology.
  • The sources of the methane plumes if confirmed. This will depend on the ESA Trace Gas Orbiter which has the potential to localize them to particular regions on Mars if they are temporary and well defined. Perhaps we find some obvious interesting feature to explore that seems to be the source.
  • Flow like features in Richardson crater. It's a great chance to observe the Martian dry ice geysers close up, but the interest for astrobiology is later in the spring when streaks start to move down the slopes at meters per day. These seem to be caused by brines, don't match dust features, not in the southern hemisphere (the northern hemisphere ones are different). If so then both leading hypotheses involve fresh water, either in thin layers, undercooled liquid water, that just might be usable by microbes - but the more interesting one involves a layer a cm or two thick. If there is clear ice anywhere on Mars then this should form a few tens of cms below the surface due to the solid state greenhouse effect which forms similar sheets of fresh water in Antarctica. This is the best candidate for a place where this may be happening We can also look for clear ice in the polar regions generally and if found, test to see if there is liquid water beneath it. Another habitat would be droplets of fresh water around sun heated grains of dust in the ice below the surface.

    That is my personal top candidate as an exciting place to visit to search for present day life on Mars. For more about it see Does Ice Act As Greenhouse On Mars - Fresh Liquid Water Habitats In Spring 10-20 Cms Below Polar Ice?
    This can be a single mission to start with. It would be good to visit the northern ones too, for comparison, but they form at temperatures too low for habitable brines or fresh liquid water to be a likely hypothesis, though very cold brines are possible for them too.
  • The Phoenix lander site - to investigate whether the droplets of liquid that formed on its legs form naturally and if they are habitable. Also to drill into the ice looking for past life and maybe long dormant but revivable life. Combine with an investigation of the lander itself to check whether any life has spread to the surrounding landscape - I come back to this later. You land a fair bit away from the lander and drive over to it, so you search an area where Earth microbes are unlikely to have reached (unless they spread rapidly) and then travel up to the lander prospecting for life as you go. You then investigate the lander itself, which is bound to have some spores on it. So this mission is guaranteed to find biology, though Earth originated. This can help test using the astrobiological instruments with a known target on Mars, as I mentioned above.
  • The sand dunes Curiosity drives over. Curiosity found evidence of a layer of liquid brines that forms just below the dust in the early morning. It's just a few cms beneath its wheels as it drives, yet there is no way to examine it. It is thought to vary between being too salty and too cold for Earth microbes - but it may be habitable to Martian life, or they may form biofilms that make it habitable even to Earth life by modifying the environment in the brines (Nilton Renno's idea)

    Again it would be useful to visit the Curiosity rover itself as well as its landing site, and test both the rover and its tracks to see if it has brought any Earth life to Mars. Especially, if there are biofilms in the liquid brines just beneath the martian sand that it drove over, has it infected them? Hopefully not.
  • The Hellas basin, deepest part of Mars, where misty clouds form and the boiling point of fresh water rises to well above O C. It's the best place to find life which relies only on the night time humidity of the air.
  • The Viking 2 lander site. Again land at a distance, approach it with a traverse, searching for life as you go. Replicate the Viking experiment with better equipment to see if you can reproduce the circadian rhythms offset from temperature fluctuations by two hours and investigate what caused them - and try feeding amino acid without their mirror image variants and see if you get the same results. Also test the lander itself to see if it has contaminated Mars, and how effective the Viking sterilization was.
    This mission could also explore the desert varnishes, and the morning frosts and test the hypothesis that a layer of higher humidity hugs the surface as the frosts melt in the morning.
    Lava tube caves Here is Penelope Boston, back in 2008, talking about potential for present day life on Mars in caves, and the possibility of exploring them with a swarm of nanobot cavebots. We could find evidence of past life in caves also
  • Other types of caves due to weathering, caused by water erosion (clay, salt and soft rock eroded in massive flooding events and perhaps caves deep below the surface from hydrothermal processes), caves carved out by the wind, caves at geological strike / slip faults, forming due to collapse of debris, ice caves in the polar regions, and even dry ice effects which may lead to types of caves we don't have on Earth.

    Most of these would be almost impossible to see from orbit, so it's not surprising that we have only found collapsed lava tube caves and similar so far. It would be a case of looking at different times of day and at an angle. One idea is to send miniature planes to fly along the Valles Marineres to photograph its walls up close and search for caves amongst other things.

Penelope Boston lists these as some of the types of cave possible on Mars:

  1. Solutional caves (e.g. on Earth, caves in limestone and other materials that can be dissolved, either through acid, or water)
  2. Melt caves (e.g. lava tubes and glacier caves)
  3. Fracture caves (e.g. due to faulting)
  4. Erosional caves (e.g. wind scoured caves, and coastal caves eroded by the sea)
  5. Suffosional caves - a rare type of cave on the Earth, where fine particles are moved by water, leaving the larger particles behind - so the rock does not dissolve, just the fine particles are removed.

She points out a few processes that may be unique to Mars. Amongst many other ideas she suggests:

  1. For the solutional caves, the abundance of sulfur on Mars may make sulfuric acid caves more common than they are on Mars. There's also the possibility of liquid CO2 (which forms under pressure, at depth, e.g. in a cliff wall) forming caves.
  2. For the melt caves, then the lava tubes on Mars are far larger than the ones on the Earth.
  3. Mars could have sublimational caves caused by dry ice and ordinary ice subliming directly into the atmosphere.

We might get more puzzling results like the Viking experiments. We know a fair bit about the surface chemistry, which may help. But if we get puzzles, not to give up but do a follow up mission.

That's ten missions to sites of especial interest. So far we have had seven successful missions to Mars. That's not including Penelope Boston's list of cave types, many of which are sure to be there, but we have to find them first. Add in a mission to fly miniature planes along the Valles Marineres to search for some of them and a follow up mission or several to visit any discovered and you are now at a dozen missions or so.

At the pace of missions to Mars at present that would take decades.

But the pace is heating up - in 2018 we might see two landers on Mars, from ESA as well as NASA and it's possible that CNSA (China) or the ISRO (India) send a lander in the near future too with increasing capabilities. If Elon Musk's BFR or some other rocket or space plane hugely reduces the cost to orbit then we may send many missions to Mars in a few years.

Great places to search for early life, with some of them of interest for present day life too, include:

For more on this, my article:

Many ways we can explore, see these sections in my Touch Mars? book:

See also my

SpaceX says the costs per launch of the BFR will be less than for the Falcon 1. If that is right, that's less than $8.5 million per flight. We may get dozens of missions to Mars at that price point.

I don't think the BFR should land on Mars for astrobiological missions because there is just no way it could be sterilized sufficiently. But it could put huge payloads into LEO or Earth capture orbits that then could boost to Mars and those would be low cost, and also would not tie his BFR up for long, it just puts a payload into orbit and it then boosts for Mars. For that matter his Falcon Heavy already reduces the cost to Mars a fair bit if it flies regularly.

If we send humans to Mars we'd send enough heavy lift to Mars to complete this preliminary survey in a couple of years. We'd probably need to do follow up missions, but if you had just some of the resources that would be available for a human mission to Mars devoted to an astrobiological survey you are talking about less than a decade.

On Earth you'd want to send missions to, say,

  • Tundra
  • Ice sheets
  • Tropical rain forest
  • Temperate forest
  • Savannah
  • Temperate grassland
  • Alpine habitat
  • Glacier
  • Lava tubes
  • etc etc

And suppose you could only send one rover to each of those sites, and it can only travel a few kilometers - how much of a complete picture of Earth's biosphere on the land would you get?

Our picture of present day and past Mars habitability and of its landscape is so complex that it's not that different. We couldn't do a thorough biological survey in a couple of decades.

What we could aim for is to complete a preliminary rather sketchy astrobiological survey of some of the main features of interest in a couple of decades if we increase the pace of missions to the point that we send several astrobiological missions to Mars with each transfer opportunity every two years.

That would be enough to get a first idea of whether some of those proposed present day habitats are habitable to Earth life, and to see if there is Mars life in any of the ones we find. If we do find life, it would let us get a preliminary idea of what type of life we are dealing with, and trace out a bit of the history of habitability of Mars and evolution of the life (if it is present).

This is just the way it is. The situation for Mars habitability is complex and to get a first idea of what we are dealing with there will take a lot of time or a greatly increased pace of astrobiological missions to Mars. This is our biggest knowledge gap for Mars.


We don't have that much in the immediate pipeline to address it.

NASA'S Insight Lander, to study the interior of Mars and its geological evolution will be the first test of a self hammering probe on Mars, a heat flow probe that will drill to a depth of 5 meters, trailing a cable with sensors on it behind it. Though sadly it won't be using this for astrobiology. The UK's Beagle 2 mission in December 2003 was equipped with a self hammering mole PLUTO capable of drilling to depths of 1.5 meters, but the mission of course failed due to one of the solar panels not opening on the surface.

Curiosity actually has one experiment on SAM, that could test for chirality, as one of the six gas chromatograph columns detects chirality Sample Analysis at Mars (SAM). It uses GC4 chirasilDex (Chiral compound separation) And apparently it is in the mass range to detect amino acids. The Mars Curiosity Rover Can Detect Chiral Compounds.

Whether or not Curiosity uses this capability, detecting chirality is well within the range of possibility for future missions to Mars. The MOMA Gas Chromatograph for ExoMars will have one chiral column of its four, coupled to its mass spectrometer and it will be able to detect a wide range of organic molecules.

ExoMars will be the first rover to Mars with the ability to drill to a depth of 2 meters making it the first mission that has a decent chance of finding traces of past organics deep enough so that it's not been destroyed by ionizing radiation.

The Mars 2020 sample caching and later return is not expected to return samples of significant interest to astrobiology unless it is very easy to find on Mars, as organics it finds on or near the future are likely to be from meteorites. Also, it is caching tubes are not going to be 100% sterile. They even tolerate a small chance of an intact viable spore from Earth in one of the tubes, so any life found could be from Earth. See my A Mars sample return would return rocks interesting for geology and would be useful as a technology demo - but would it help the search for life? in my Touch Mars? book.


You might think the main thing we'd lose is information - the cells themselves don't matter, but the information about them does. But actually, we need the living cells themselves, into the foreseeable future. I dare say McCoy on Star Trek could make a living cell from a pattern in a database. But that's far beyond us.

To see that, suppose it's a slightly different story - you manage to work out how an RNA world cell works in great detail before it goes extinct. You sequence the genome. You work out the details of construction of the cell wall. You find out the chemical structure of all the ribozymes and work out all the biochemical processes that are going on in the cell in great detail. You work out how the instructions of the genome are converted to chemicals in the cell. And now finally it goes extinct but you have found out enough information to pretty much know how it works.

Let's go a step further. Maybe it is so small and reasonably simple in structure, only a few hundred distinct molecules, say, you can simulate an entire RNA world cell in a computer and simulate how it works digitally.

Still, you can't make it in reality. Because of the herding cats problem.

We have come across this in a simpler way with synthesis of a genome. It's far easier to analyse a genome than to make one.

It took fifteen years to get from the first sequenced genome to the first synthesized genome of a real living cell.

Synthesizing a genome is probably many orders of magnitude easier than making a complete working cell from nothing but chemicals.The biomedical engineer James Collins at Boston University was reported in the Wall Street Journal as saying at the time:

"I don't think it represents the creation of an artificial life form. I view this as an organism with a synthetic genome, not as a synthetic organism. It is tough to draw where the line is."

So, for example, if you knew how an RNA world cell worked, and then made the RNA genome, it probably wouldn't work at all in a modern DNA based cell, without all the translation machinery needed to convert those instructions into whatever it uses for its biochemistry. You have to have all the rest of the structure of the cell there as well. Even though the genome determines the cell, the genome can't get started doing its thing until the cell it determines is already there to support it.

So, even if we had worked out how an RNA world cell should work in a computer - and we are nowhere near being able to do that AFAIK - we still couldn't make on.

What you need is

  • a sequence of chemical reactions that ends up producing that cell as an endpoint.
  • a way of converting a DNA based cell into an RNA world one.
  • or some kind of hybrid, some chemistry and some biology (as was done for the first synthetic genome - it was made using chemistry but multiplied up to many copies of each fragment using cells)

If it is sufficiently different then there may be no way to make that conversion, including the case where it is a much simpler form of cell. Maybe you are lucky and enough of the original machinery has somehow been inherited in the modern cell to scavenge it somehow to make your RNA world cell. But if not, tough. You are then left with the first possibility of making it through a sequence of chemical reactions as essential for much of the process. That would be very tough to do. Even though that is how it evolved originally, or at least, its first precursor cells.

There's a big gap between understanding in principle how an RNA world cell would work, if we get that far, and actually building one.


For those who are not especially interested in astrobiology I think it's worth saying that there are many possible discoveries and advances can come from discovery of new biology in space.

Understanding our origins better yes. Understanding how our own biology works better also by seeing how biology works with cells that work differently with different coding systems, ways of replicating, different enzymes, maybe life without any proteins such as RNA cells. Yes all of that. But it may be only the "tip of the iceberg". For instance, it may lead to multi-billion dollar industries.

I found this in an article by Charles Cockell:

"In uncovering the secrets of life's survival on the Earth, astrobiology has some found remarkably prosaic applications. The powder that works in your washing machine at high temperature functions because it contains proteins extracted from microbes that grow in volcanic hot springs."

" They were first found by scientists (who would today call themselves astrobiologists) seeking to know how life adapts to such primitive, searing surroundings."

From "How the search for aliens can help sustain life on Earth", Charles Cockell op ed special to CNN, October 2012.

Intriguing isn't it?

These enzymes are now used

  • in the food industry, including bread making, fruit juices, for lactose free foods, for making syrups
  • in the $1 billion industry of enzymes for detergents - this is another application - they work at cold temperatures so removing the need for heating and saving energy.
  • for wood pulp and paper processing
  • in the textile, cement, cosmetic industries.
  • in various research techniques for experts studying DNA and RNA

They are used to reduce costs, make the processes more ecofriendly, reduce CO2 emissions, enable more efficient faster processing, etc etc.

They come in two main categories, enzymes from cold adapted, and from heat adapted extremophiles.

The cold adapted enzymes are more active, and active at lower temperatures. This means you need less of them to get a result, and you don't have to heat them up and they can work at low temperatures. As an example, this lets you reduce washing temperatures and to help people with limited access to warm water. The global market for detergent enzymes is valued at over $1 billion.

The heat adapted enzymes are active and efficient at high temperatures, extreme pH values, high concentrations of the substrate, and high pressures. They are also highly resistant to organic solvents, and other things that stop enzymes working (denaturing agents). They are easier to separate during purification steps (because they don't break up) and they catalyze faster reactions.

I cover this in these sections of my book Touch Mars? Europa? Enceladus? Or a tale of Missteps? :

They summarize details from this long technical paper: Cold and Hot Extremozymes: Industrial Relevance and Current Trends (paper from 2015)

If what we find on Mars is related to Earth life, but evolved on a planet with night time temperatures cold enough for dry ice, extreme desiccation, high levels of UV, and of ionizing radiation, pervasive perchlorates and hydrogen peroxide etc - we may well find extremophiles there that push the limits far beyond what Earth extremophiles can do.

Who knows what the applications would result from a new biology from Mars in the most interesting and I'd say "best case"? The case where there is a significant potential issue of contamination, yes, but also major discoveries to be made.

This could go far beyond discovery of some new enzymes. It could have applications in medicine, agriculture, nanotechnology, new materials for industry; there is simply no way of knowing what the results could be of such a revolutionary discovery as life based on different principles from Earth life, even if it is just microbes.

If we make Mars life extinct, then we are robbing not just ourselves but our children, grandchildren and all future generations from the countless benefits that may follow from the discoveries they could make by studying it.

Cassie Conley before Elon Musk's BFR announcement said:

“The excitement over this pending announcement overshadows a worrisome dilemma: The special regions where Earth life could take hold are also the areas where we would most likely find indigenous Martian life. That means—unless we are very, very careful—we could ruin our chances of discovering extraterrestrial organisms just by going to look for them."

“It’s like looking for stars when the sun's out. If you want to find Mars life, you have to get rid of the signals of Earth life so that you can see it."


One of the things that makes a planetary protection officer's job hard is that there is so little awareness amongst the general public and even other scientists, even today, of the need for her job, and why we care about whether Earth microbes might make Mars life extinct, or confuse our studies of it. Many in the general public probably even don't know this debate is going on.

Nor politicians either. How many senators or congressmen or women know about this debate when they vote on directives for NASA? How many presidents? Was President Obama aware of this debate when he set the objective to send humans to Mars? How many know of the debate in any detail, even of those who are involved in responding to the decadal reviews which are used as feedback from the space community to help set NASA's objectives for the next decade?

Even astronomers and scientists who work in the space industry are often not aware of this debate. Particularly the many ramifications that could follow from our microbes landing on Mars.

I hope this article can help bring more public awareness of this debate. It is the first step if we are going to make a wise decision, to discuss it and think about it.

In this debate, there are many groups of people with different emphases and priorities working together.

  • Hopeful Mars colonists who are vocal, organized under the umbrella of the Mars Society. They are an advocacy group and every year, they lobby Congress to support their views. They want humans on Mars as soon as possible and ask why we aren't there yet.
  • Geologists who would love to have humans on the surface of Mars to study the rocks there. Their main focus is to continue to do what they know how to do, to find out more and more about the chemistry and geology of Mars.
  • Astrobiologists who write papers in the academic journals about their views. But they don't have a vocal lobbying group, and for historical reasons are not much involved in decision making for space missions, not since the two Viking landers, our first and last astrobiological missions to date. Their priority is to send astrobiological instruments to Mars to search for life in situ. The only ones that get much publicity are the few ones proposing "dirty robots" as their papers are promoted by the Mars colonist enthusiasts. The responses to those papers by the planetary protection officers tend to be ignored.
  • Planetary protection officers and the contributors to COSPAR workshops - and some others who specialize in planetary protection such as Margaret Race of SETI - who are tasked with upholding the Outer Space Treaty and who have spent their professional lives studying the various things that could go wrong - and urge caution.

So far the planetary protection officers have been the main representatives of those more cautious astrobiologists. But few people have heard their point of view either amongst the general public although they do a lot of public outreach work.

In their quiet way I think they are just presenting common sense myself. We should all listen to them, because they are the ones who have the most in depth and detailed understanding of what the issues are and how things could go wrong, badly wrong.

It's been their job to protect Mars and other celestial bodies, as well as the Earth (for anything returned here from space), and they have devoted their working life to this. They are backed up by many other astrobiologists who have similar views that they have published in papers and who have also looked in detail at planetary protection issues.

I hope this article helps make their task easier. I see it as my contribution towards their public outreach about planetary protection. But as someone not involved in any way with planetary protection decision making, I am free to make forthright statements about planetary protection issues, to hopefully get people thinking about this, without anyone asking me if this means a policy direction change for NASA or COSPAR :).


I'm not an astrobiologist, I approach this as someone trained as a mathematician who specialized in the philosophical studies of mathematical logic for several years of postgraduate study. I've had a long term interest in science generally and astronomy and space missions particularly since a child, from long before the first astronauts landed on the Moon. Patrick Moore who did a monthly Sky at Night series on BBC television in the UK was one of those who first got me enthused about space with his broadcasts. With my mathematical and scientific background, the specialist papers on this topic are easy to read and I've read many of them over the years. I am not expert in any of the topics in this field. But nobody could be expert in them all.

That helps I think, to get a wide overview of the subject, as someone who is not immersed in the field, so having a bit of a distance from it. I have no personal involvement, and no research I'm doing myself depends on planetary protection decisions. Neither am I in a hurry to get some experiment done, nor am I personally involved if we extinguish Mars life. Also I have a strong background in maths, logic, philosophy and ethics, which helps a lot with clear thinking about "fuzzy ideas" such as hypothetical biologies on Mars. I think this helps me to take a broader view on it all.

I have written three books on this topic of humans in space and ways to do both - to explore in space with humans in an exciting and ambitious way - and at the same time to do it responsibly, to protect both Earth and other planets and to leave the future open so that scientists can continue study of exobiology on Mars and in other places for as long as is needed, for the foreseeable future if it comes down to that.

My Touch Mars? book also looks at the history of planetary protection and some of the many possible locations for life in our solar system, and indeed elsewhere, and how we can search for it. Further into the future it raises the broader question of whether we need "Galaxy Protection" once we develop the capability to visit other stars, and I explore the idea of Galaxy Protection as one solution to the Fermi paradox of "where is everybody?" I also cover nitty gritty questions such as trash on the Moon, how you would grow plants in space, possible science surprises from our explorations and many other topics. I look at the practicality of human settlement and look at questions that might arise as we try to send humans further and further afield into our solar system.

I hope it's a fun read. The sections are self contained as far as possible so that you can use it as a book to dip into, rather than one you read from cover to cover.


You can read my Touch Mars? book free online here:

Touch Mars? Europa? Enceladus? Or a tale of Missteps? (equivalent to 1938 printed pages in a single web page, takes a while to load).

Also available on Amazon kindle. It is designed for reading on a computer with embedded videos and links, and I have no plans to attempt a printed version.

As far as I know it's the first book devoted to planetary protection since "When Biospheres Collide".

My other books, which cover human exploration as well as planetary protection, and explore the case for going to the Moon first (for humans), are:


And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon



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