This is a news story that broke recently, on the idea that Elon Musk's plans would violate the Outer Space Treaty. The articles I've read so far focus on property rights and the  provisions in the OST that rule out ownership of territory. But that can be fixed with future legislation, especially since it's not really the land but the habitats that are of most value, and ownership of those is already covered in the OST . So far none of them have mentioned by far the toughest legal and practical obstacle, which is planetary protection of Mars from Earth microbes to preserve its science value for the future of mankind. That can't be fixed by passing new laws. Elon Musk says the mission would be dangerous, with colonists risking death, especially the first ones. The biggest danger is on landing, and a crash of a human occupied ship on Mars in a Challenger type accident would strew fragments of bodies, food, water, air, and spacecraft over the planet. That would be pretty much the end of any planetary protection of Mars.

The planetary protection requirements are not just a result of decisions by fussy bureaucrats. The ones responsible are concerned astrobiologists, such as Carl Sagan and Joshua Lederberg (nobel prize winning pioneer in microbial genetics), and built up in detail over many discussions by international groups of astrobiologists and other scientists in biannual meetings of COSPAR. Nor is it a minor concern of detail. They are concerned that we could rob ourselves and future generations of discoveries in biology as fundamental as the discovery of the helical structure of DNA or the theory of evolution.

So far every space faring country has taken care to sterilize their spacecraft if necessary and abide by the provisions of the OST as interpreted by the COSPAR meetings and guidelines. Most have signed and ratified the Outer Space Treaty and even the United Arabic Emirates, who haven't ratified it yet, say that they will take care to abide by its provisions if they succeed in their plan to send a mission to Mars. It just makes sense to do so.

Joshua Ledeberg at work in a laboratory at the University of Wisconsin 1958, nobel prize winning pioneer in microbial genetics and pioneer in the field of planetary protection along with the astrobiologist Carl Sagan. He was one of the first astrobiologists, indeed he coined the word "exobiology"
Then, Curiosity's "seven minutes of terror" wasn't just hyperbole. There was a real risk that it would crash, especially with such novel technology, with many previous examples of crashes on Mars. This is especially tricky with the Mars atmosphere too thin for a conventional parachute to work by itself - but with the gravity too much for a lunar module type landing. You need to refuel to get back to orbit again.

Elon Musk's idea is to use supersonic retropropulsion. The rocket lands on the Mars surface in reverse. It has to use the atmosphere for aerobraking, and simultaneously fires its rockets to bring it to a standstill on the surface. The atmosphere is only thick enough for this close to the surface, so it skims down to a landing within a few kilometers to the surface - so close that it can't land on mountainous areas of Mars because the air is so thin. 
Artist's impression of red dragon doing supersonic retropropulsion over Mars, image SpaceX

It's no wonder that he said in the talk that the mission to Mars carries a high chance of death for the first would be colonists. It will surely take a while to perfect this technology. Even if say, he has four successful previous unmanned missions, this doesn't prove it is safe. With a 50/50 chance of success for each mission, you can get four successes in a row with a 6.35% probability. So four successes would not show at all conclusively even that it is 50% reliable. Other ideas such as enormous parachutes far larger than any tested to date also have similar issues.
So, if we accept that there is a high risk of a crash, how can you be sure you won't get this sort of thing happening?

Debris from Columbia - broken into tiny pieces by the crash. if something like this happened on Mars, with the debris spread over the surface and dust and small debris and organic materials from the crash carried throughout Mars eventually in the global dust storms - that would be the end of any chance of planetary protection of Mars from Earth life.

The planetary protection office, and COSPAR have discussed human missions to Mars. There is no set out protocol yet, but in their preliminary discussions they suggest human missions confined to a particular area of the surface. They accept that this is an irreversible introduction of Earth microbes to Mars and just aim to limit and delay the impact.

However they do these planetary protection assessments of human missions to Mars based on the assumption of a successful landing on Mars. They don't consider the possibility of a crash as that's left to mission planners at a later stage. Yet, for robotic orbiters Mars is treated as a Category III mission and needs to be sterilized to levels that will make the mission safe in case the orbiter crashes on Mars!

At some point someone has to consider what the effect would be of a human crash on Mars, and once you consider that, and if you assess the planetary protection issues for it, I don't see how anyone could either say that a crash won't happen, or that a crash would be anything short of a total end of protection of the planet. It might not be the planetary protection office that do this, if they continue with this policy of assuming 100% successful landings in their assessments. But someone has to do it.


I think that an orbiter mission for humans on Mars also needs assessment for the possibility of a crash on Mars just as for robotic orbiters. There could be ways to make it safe enough so that the possibility of a crash is for practical purposes non existent.

First, I think flyby missions like Robert Zubrin's Double Athena Flyby could be made sufficiently safe for planetary protection. This is an interesting mission that does two flybys of Mars and in between orbits almost parallel with Mars for half an orbit or one Earth year. The crew are close enough to the surface of Mars for telepresence style telerobotics for of order of hours, for both flybys, and are within close range of the planet for days.

Flybys can be done accurately, we've done multiple flybys with Cassini and other spacecraft. We haven't yet had a crash during a flyby mission. You'd use trajectory biasing, so that the final stage misses Mars, and so that if something goes wrong the human occupied spacecraft also misses Mars, and then do gentle nudges to keep it on target, and months during which you can refine the orbit and make sure you are on target.

I think that an orbital insertion maneuver though could go wrong and lead to humans crashing on Mars as has already happened, with the Mars climate orbiter.

Another type of transfer though is very safe - that's ballistic capture. In this approach, the spacecraft is launched to arrive in a distant orbit around Mars, at just the right speed so that it is captured by Mars as a temporary distant extra minimoon with no need for an insertion burn. The crew then can use ion thrusters to slowly modify their orbit to get close to Earth for telepresence during part of the orbit. Ion thrusters change orbit so slowly, that there's not really any significant risk of them accidentally impacting on Mars. So it's much safer for the crew also, and I think probably has no significant planetary protection risks.

This would need to be looked at carefully, and you need to consider also whether any waste material ejected from the spacecraft could hit Mars, but it does seem you could have human missions to Mars that don't need to be sterilized to the levels needed for robotic orbiters to date, without compromising on planetary protection.


Extremophiles that also live in human habitats and found in spacecraft clean rooms can survive in the suggested habitats on Mars if they exist and many have hardy spores and other dormant states that could be carried in the global dust storms throughout Mars. Humans are not the problem, the microbes that inevitably come with them are. After that, any searches for present day life on Mars would need to have as the default hypothesis that what they find was brought to Mars on that crashed human mission, an enormous impact on scientific exploration of Mars.

It would not be "easy to distinguish" as Zubrin suggests with the analogy of anthrax, as only 100,000 of one trillion microbe species, 0.00001% have had gene sequences published. It's not at all practical to have an "inventory" of every single microbial species on the spaceship.

Also archaea swap DNA fragments very readily via horizontal gene transfer so could do that with life on Mars, if related, by an ancient mechanism that goes back billions of years. If related, even if the common ancestor came from lifeforms that seeded our solar system from another planet around another star at birth via panspermia, then the DNA could get mixed up to the extent it is hard to tell what came from Mars and what from Earth.

But most vulnerable would be some early form of life. There's the shadow biosphere hypothesis for Earth that there might be tiny RNA lifeforms here with no DNA or proteins, so having much smaller cells. None have been found, and if that was what came before modern life, it is probably extinct here, as also all other suggestions for life precursors. They may perhaps still survive on Mars. If so then modern life could make them extinct on Mars just as it did on Earth.

Or the life on Mars could, some or all of it, have followed a different direction that makes it vulnerable to Earth life. That juts needs Earth life to have a slightly more efficient metabolism, or to be slightly better at photosynthesis, say, and it could over time take over from Mars life completely. It could of course also work the other way that Mars life is slightly better than Earth life and takes over from Earth microbes in the soil water etc. That we have exchange of materials between Earth and Mars doesn't rule this out because it happens rarely, after meteorite impacts large enough to send material all the way to the other planet, and the material takes from a century to millions of years to do the transit, in the deep cold of interplanetary space, vacuum conditions, has to withstand the shock of ejection and re-entry, the material sent into space comes from some meters under the ground in the spreading crater, and it has to be able to survive when it gets there, find a suitable habitat. Compare that with landing on the surface of Mars immediately from a crashed human ship and it is clear that many lifeforms could get to Mars in the ship that couldn't get there by any other way. It's also a matter of probabilities, introduce trillions of microbes in one go, compared with a few in a few species, over millions of years. One method used to assess whether missions need planetary protection is to look at the "natural contamination standard". We get material all the time from comets or asteroids so it is not considered hazardous to Earth life to return those materials to Earth. But there is no similar natural process corresponding to a human spaceship crashing on Mars.

And in addition, the scientific experiments would look for the most sensitive of traces. Detecting life by chirality of amino acids, or by metabolic activity. Those exquisitely sensitive instruments would be useless if there is Earth life there already introduced by a human crash on Mars.


(This repeats material from the article I posted a few days back: )

Elon Musk does care about the science impact of introducing Earth microbes to Mars. Here he answers a question on this topic, in the 2015 AGU conference in San Francisco, 30 minutes into this video:

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

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

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

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

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

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

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

Most of those habitats are either above the permafrost layer or at most a few centimeters below it (the permafrost layer is typically 2 cms below the surface of Mars or less).

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

If these habitats do exist and are habitable, there are many Earth microbes which have been shown to be able to survive in Mars conditions in Mars simulation conditions, and so could potentially survive in these habitats on Mars if they exist.

Researchers at DLR (German equivalent of NASA) testing lichens in Mars simulation experiments. They showed that some Earth life (Lichens and strains of chrooccocidiopsis, a green algae) can survive Mars surface conditions and photosynthesize and metabolize, slowly, in absence of any water at all. They could make use of the humidity of the Mars atmosphere.[46][47][48][49][50]

Though the absolute humidity is low, the relative humidity at night reaches 100% because of the large day / night swings in atmospheric pressure and temperature.

I did a survey of the literature a while back and compiled a list:

  • Chroococcidiopsis - UV and radioresistant can form a single species ecosystem, and only requires CO2, sunlight and trace elements to survive.[50]
  • Halobacteria - UV and radioresistant, photosynthetic (using a different mechanism), can form single species ecosystems, and highly salt tolerant. Some are tolerant of perchlorates and even use them as an energy source, examples include Haloferax mediterranei, Haloferax denitrificans, Haloferax gibbonsii, Haloarcula marismortui, and Haloarcula vallismortis [59]
  • Some species of Carnobacterium extracted from permafrost layers on Earth which are able to grow in Mars simulation chambers in conditions of low atmospheric pressure, low temperature and CO2 dominated atmosphere as for Mars.[141][140]
  • Geobacter metallireducens - it uses Fe(III) as the sole electron acceptor, and can use organic compounds, molecular hydrogen, or elemental sulfur as the electron donor.[200][203][204]
  • Alkalilimnicola ehrlichii MLHE-1 (Euryarchaeota) - able to use CO in Mars simulation conditions, in salty brine with low water potentials (−19 MPa), in temperature within range for the RSL, oxygen free with nitrate, and unaffected by magnesium perchlorate and low atmospheric pressure (10 mbar). Another candidate, Halorubrum str. BV (Proteobacteria) could use the CO with a water potential of −39.6 MPa [202]
  • black molds The microcolonial fungi, Cryomyces antarcticus (an extremophile fungi, one of several from Antarctic dry deserts) and Knufia perforans, adapted and recovered metabolic activity during exposure to a simulated Mars environment for 7 days using only night time humidity of the air; no chemical signs of stress.[55]
  • black yeast Exophiala jeanselmei, also adapted and recovered metabolic activity during exposure to a simulated Mars environment for 7 days using only night time humidity of the air; no chemical signs of stress.[55]
  • Methanogens such as Methanosarcina barkeri[200] - only require CO2, hydrogen and trace elements. The hydrogen could come from geothermal sources, volcanic action or action of water on basalt.
  • Lichens such as Xanthoria elegans, Pleopsidium chlorophanum[53], and Circinaria gyrosa - some of these are able to metabolize and photosynthesize slowly in Mars simulation chambers using just the night time humidity, and have been shown to be able to survive Mars surface conditions such as the UV in Mars simulation experiments. [205][206][207][208][209]
  • Microbial life from depths of kilometers below the surface on the Earth that rely on geochemical energy sources - relying on metabolic pathways that can't be traced back to the sun at all. Some of these are multi-cellular. Examples include the microbe Desulforudis audaxviator which metabolizes reduced sulfur as the electron acceptor, and hydrogen as the electron donor, can fix nitrogen and has every pathway needed to synthesize all the amino acids [210][211]
  • Multicellular life from depths of kilometers below the surface such as Halicephalobus mephisto, a nematode feeding on bacteria, 0.5 mm long and up to 3.5 km deep, lives in water at 48°C, very low oxygen levels about a thousandth of the levels in oceans. Though it probably originates from the surface, carbon dating shows it has lived at those depths for between 3,000 and 10,000 years, and it's been suggested that this has implications for deep subsurface multi-cellular life on Mars.[212]

Most of these candidates are single cell microbes (or microbial films). The closest Mars analogue habitats on Earth such as the hyper arid core of the Atacama desert are inhabited by microbes, with no multicellular life. So even if multicellular life evolved on Mars, it seems that most life on Mars is likely to be microbial.

Because of the low levels of oxygen of 0.13% in the atmosphere, and (as far as we know) in any of the proposed habitats, all the candidate lifeforms are anaerobes or able to tolerate extremely low levels of oxygen. This also makes multicellular animal life unlikely, though not impossible as there are a few anaerobic multi-cellular creatures[213]. Some multicellular plant life such as lichens, however, may be well adapted to Martian conditions (this was a bit of a surprise to the researchers as lichens are symbionts of algae and fungi, and fungi need oxygen - however, it seems that the algae supply enough oxygen for the fungus even when there is hardly any oxygen in the atmosphere around them).

Also some multicellular life such as Halicephalobus mephisto can survive using very low levels of oxygen which may perhaps be present in some Mars habitats.

(This is a copy of my section Candidate lifeforms for Mars in my booklet Places on Mars to Look for Microbes, Lichens, ...)

Most of these can live in the postulated surface or near to surface habitats. The habitats deep below the surface would be less affected by microbes introduced to the surface, but as on Earth, Mars will have caves and crevices that link to the surface, as a result of meteorite impacts, water erosion and crustal movement (the meteorite impacts especially fracture the surface of Mars to considerable depth). Also the methane plume observations, if confirmed, suggest a connection between the deep subsurface and the atmosphere. So I included those as well, as I'm not sure that the subsurface can be treated as totally insulated from the surface, though the surface habitats of course are the ones of most immediate concern.

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

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

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

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

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

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

For more on this see Value of a non confrontational approach and following in the book.

It is an open question in exobiology, whether Mars life would be related to Earth life or not. The theory of panspermia is just a theory and even if there is some shared life, there could also be life that is not shared. A journey of a few thousand or hundreds of thousands of years in the cold and vacuum of space is not the same as a journey of a few meters from a spacesuit (they leak air and microbes all the time) to the ground. Even if some very hardy lifeforms from Earth have got to Mars, which is not yet known, most microbes would have no chance of making that journey on a meteorite.

The problem is that the Mars surface is interconnected, with the global dust storms. So, if these habitats exist, any life brought to Mars will gradually spread to the entire planet through hardy microbial spores, protected from the UV light imbedded n cracks in the dust. Once that is started, it can't be reversed. And as Elon Musk says, human missions to Mars will be dangerous with significant chance of loss of life. One of the most dangerous times in the mission would be the landing on Mars. After a human mission crashes on the Mars surface, that would be the end of any chance of protecting Mars from Earth life, with debris, tiny fragments of the astronauts bodies, air, water, food, scattered across the surface and the spores spread in the dust.

The introduced life from Earth could easily out compete Mars life. I think the easiest example here is the example of some earlier form of life that has been made extinct on Earth but still lingers on Mars.

One good example is RNA based life, which could exist without DNA or protein. These "RNA world" cells were hypothesized for a shadow biosphere here on Earth. So far we haven't found these cells on Earth, so if this form of life existed here in the past, perhaps DNA based life made it extinct. If so, what if it still exists on Mars? It might well be vulnerable to whatever made it extinct on Earth, from introduced Earth life. See One example of what we might find on Mars is some early form of life made extinct on Earth by DNA based life 

Or, it could be some completely unrelated form of life, in which case again, there is no reason particularly why it has to be invulnerable to Earth life, or indeed vice versa, maybe in the harsh Mars conditions it has evolved capabilities our life doesn't have, and Earth life could be vulnerable to it. A good example there - if it has a more efficient metabolism, or is marginally better at photosynthesis, then it could out compete Earth life, and vice versa, Earth life could out compete it. It wouldn't need much of an edge there, just a tiny edge due to Earth life's different biochemistry, and over many generations of microbial cells the Earth life would predominate. Just doubling once a month, if it has a significant advantage over Mars life, it wouldn't take long for every cell in a small habitat to be Earth life, and then if it spreads through spores in the dust, then it might not be many years before most of the habitats Mars wide are colonized by Earth life. And whether or not it happened as quickly as that, there would be no way to halt or reverse such a process once started, once you have spores in the dust and the life has spread significantly beyond its original first colonized habitat.

I'm not saying, don't go to Mars. But we can do a lot from Mars orbit. Meanwhile the Moon is the safest place to do early experiments in space settlement. It may have lunar caves up to 5 kilometers in diameter and over 100 kilometers long, according to the Grail data, already set up with radiation and regolith shielding. See Lunar caves and Lunar caves as a site for a lunar base We can also use materials, first from the Moon and NEOs, later from the asteroid belt to build colonies in space with up to a thousand times the population of Earth, see Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths. We have the potential of the Venus clouds as well, see my Will We Build Colonies That Float Over Venus Like Buckminster Fuller's "Cloud Nine"?

There are only three places in our solar system of the many we can visit that we need to take especial care with

  • Mars
  • Europa
  • Enceladus.

There are a few others, that need preliminary assessment before we can say. Ceres is the obvious one with its water plumes, but there are many other bodies we know little about at present that might turn out to be biologically interesting as possible places for present day life habitats, which we can't assess adequately at present but may need care.

All these are places we can explore by telerobotics using increasingly capable robots, also explore using robots controlled from Earth. 

There is no need to send humans to these places as quickly as possible. It won't help to make us multiplanetary, but it may mean we miss out on discoveries about the origins of life, and other lifeforms. Imagine if you could learn about life on a planet or in the ocean of an icy moon around another star? Even if it was just extraterrestrial microbes or lichens, imagine how exciting that discovery would be? Well Mars, Europa and Enceladus may be like exoplanets and exomoons in our own solar system, they may be as interesting as that. We don't know until we study them close up.

It's the aspect of our exploration of the solar system that gets most interest of all from the general public I think. And if we did find an early form of life, or something significantly different, it would be the greatest discovery in biology since the discovery of evolution, or perhaps the discovery of the helical nature of DNA, of that order of importance. Who knows what implications it would have, if you think of how much of modern biology comes from those two discoveries.

If we introduce Earth microbes to them, accidentally or intentionally, this may well be irreversible. It's the irreversibility that's the issue here. If it is biologically reversible, not so much of a problem. But if irreversible, that means it would change those places for all future time, not just for us, but for our descendants and all future civilizations that arise in our solar system, they won't be able to make the discoveries they could make by studying these places as they are now, without Earth microbes introduced to them. They also won't be able to transform them in other ways if they decide they wish to introduce a different mix of microbes from the ones we brought there.

I think we just know far too little to make such a decision for all those future generations and civilizations and indeed for ourselves. At present anyway. Future discoveries of course can change this.


  • Early life, e.g. tiny RNA world microbes without DNA or proteins
  • Life based on different principles. The interior of a cell is so complex it's been compared to an entire ecosystem. So life based on different principles could be as revolutionary for biology as discovering a coral reef for your first time, when the only ecosystem you knew about before is the African Savannah. I make this analogy here: "Super Positive" Outcomes For Search For Life In Hidden Extra Terrestrial Oceans Of Europa And Enceladus
  • Life with a capability Earth life doesn't have, e.g. a new form of photosynthesis. We have three ways of doing photosynthesis on Earth - broadly speaking. Plants and some microbes produce oxygen from water, some microbes produce sulfur from hydrogen sulfide (sulfur bacteria), and some use the light to power a "proton pump" producing ATP directly from hydrogen (purple bacteria such as the haloarchaea, using bacteriorhodopsin similar to the rhodopsin in our eyes, instead of chlorophyl). So what if life on Mars has a fourth way of doing photosynthesis. Though not so totally revolutionary as an early RNA lifeform or a different biochemistry, it would still be an extraordinary discovery and major event in biology. Those are just examples. We can't know in advance what we will find but it does have potential to be revolutionary. 
  • If similar to Earth life in most respects, we can learn from the differences, how it evolved in such a different environment, since last transfer from Earth, surely at least tens of millions of years ago. We can also test the theory of panspermia, find out in practice how easy it is for life to be transferred to another planet.
  • If there is no life, we learn a lot about what happens on a world with organics and all the ingredients for life but no life. We can also learn to distinguish between the effects of life and non life on a planet - on Earth it's impossible to study uninhabited habitats, except for a very short time after a volcanic eruption. Life appears rapidly. On Mars, we might have the opportunity to study uninhabited habitats on a planet that hasn't been inhabited for billions of years. This could help us to understand exoplanets and the origin of life and maybe find out that life is harder to evolve than we thought. It can also help to disentangle effects of life and non life processes on Earth.

All possibilities here are of exceptional interest for biology. If there are habitats for life at all on Mars, whether inhabited or uninhabited, then biologists world wide will want to study them as they are now, and the results in the best case could be revolutionary for biology.

Many say this., lead by Bill Nye also have the policy that we should explore Mars from orbit first. Here is a quote from Emily Lakdawalla, in her article about NASA's Mars Announcement: Present-day transient flows of briny water on steep slopes:

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

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

NASA's planetary protection officer Cassie Conley also has talked about the advantages of exploring Mars from orbit first for purposes of planetary protection (see her appearance on David Livingston's the SpaceShow), and she makes strong statements about Elon Musk's rapid colonization plans for Mars, for someone speaking as a NASA planetary protection policy spokesperson, in an interview just before the announcment here: Cassie Conley. Going to Mars Could Mess Up the Hunt for Alien Life

I take this a bit further than them. I don't think we should just postpone it a decade and try to do as much scientific exploration as possible before doing irreversible contamination of Mars with a fixed deadline like that. I think that we should hold off from sending humans to Mars until we have done an adequate exploration, and make future decisions when the time comes based on whatever we discover next about Mars. However as both of them say, and others also, we can do safe exploration of Mars from Earth and also with humans in Mars orbit.


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

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

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

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

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

Then, you'd also have broadband streaming from Mars. As well as being very safe, also comfortable for the crew, you'd also have wide-field 3D binocular vision. It's amazing what a difference this makes, I recently tried out the HT Vive 3D recreation of Apollo 11. We'd have similar 3D virtual reality experience of the Mars surface.

Also, it would actually be a much clearer vision than you'd have from the surface in spacesuits, digitally enhanced to make it easier to distinguish colours (without white balancing the Mars surface is an almost uniform reddish grayish brown to human eyes)|.

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

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

It would be far faster. Curiosity has traveled 15.639 km as of writing this, and traveled 168.45 meters on its drive number 239 which I think is the furthest it's traveled in a day, Lunakhod 2 traveled more than a kilometer a day. That's with 1970s technology. A modern rover with modern technology, autonomous collision avoidance etc, could travel many kilometers an hour controlled from orbit, and do thousands of kilometers a year if needed. Astronauts in orbit could do delicate experiments such as we already do on Earth via telerobotics. Many modern surgical operations are done via telerobotics with the surgeon in the same room as the patient for safety reasons. However experimentally an operation, the Lindbergh operation, was done on a patient in France by a surgeon in the US with French doctors at hand in case of anything going wrong and it went just fine. There are many other examples of telerobotic surgery over distances of hundreds of kilometers or more since then. We can definitely do delicate experiments on Mars by telerobotics.

Robert Zubrin often mentions a telerobotic simulation in which a rover drove right past interesting fossils which humans on the ground could see easily. However it depends a lot on how you do the telerobotics. Exploring with a mouse and keyboard and looking at a computer screen is different from exploring using immersive binocular vision, so that you have a sense of depth, linked to your head movements so that you can just look around to see things, and haptic feedback so you can feel the rocks. You also get automatically enhanced vision. The red sky of Mars makes the rocks all a dim brown and it is hard for geologists to distinguish rocks without digital enhancement, which is why nearly all photographs from the Mars surface have the blue light levels enhanced to simulate light conditions on Earth. This would be automatic if you used telepresence. Everything you see is also streamed back to Earth for anyone to go over and look at again in case you missed anything, while nobody can double check what you saw as an astronaut on the surface unless you take photos or video. And you don't have to suit up to explore, a process that can take a long time, with many safety checks, and you don't take the risks of an EVA - the most dangerous part of any space mission - every time you want to explore the surface in person. You just put on the telepresence gear and you are there right away in immersive reality on the surface of Mars.


As for how long it would take to do a biological survey of Mars, Carl Sagan took a figure of 60 landers, 57 of those successful, and 30 orbiters, all devoted to biological exploration like Viking, as a starting point. So that's as good an estimate as any. The ability to explore from orbit would help hugely.

It's just a preliminary survey, there are a dozen different types of habitat to explore, and you have an area the size of Earth's land mass, so it is like landing eight rovers on each of the seven continents on Earth. You would get a first rough idea. But you wouldn't find some rare lifeform in some unexpected location.

I don't think we should say in advance what counts as a completed survey - as we would find out things as we go that would help us understand how complete it is, which we can't know in advance. But exploration from orbit by telerobotics, and sending lots of small robots to Mars would speed it up a lot. For more on this, see How many years are needed to do a biological survey of Mars?


I've actually worked for some time on an alternative vision, based on exploring the Moon first, as the gateway to the entire solar system. Not in the sense of a "pit stop" but a place of great interest in its own right and also resource rich, which happens to be just next door to us.

Amongst the main guiding principles, I wrote that:

  • Until we know a lot more than we do now, we should not close off future possibilities for ourselves, our descendants and all future civilizations on Earth, but should keep all options open.
  • In this approach, planetary protection and biological reversibility are core principles.

The Moon in this vision is a gateway to the solar system, a place to develop new techniques and explore a celestial body that is proving much more interesting than expected. Along the way, we are bound to get human outposts in space, and colonization may happen also.

However, settlement in space doesn't need to be the driving force, any more than it is the driving force behind the study and exploration of Antarctica. If we try to turn Mars and other places in space into the closest possible imitations of Earth as quickly as possible, this may close off other futures, like the discovery of vulnerable early life on Mars, or better future ways to transform Mars.

Once we develop the ability to live in space for years at a time, the whole solar system will open out to us. While keeping future options open on Mars we can explore Venus, Mercury, asteroids, Jupiter's Callisto and further afield, and Mars itself via telepresence. We also have many experiments in human settlement to try closer to hand on the Moon. This can be an exciting future, with humans working together with robots for remote exploration, as our mobile sense organs and hands in the solar system and galaxy.

However it doesn't mean we can never send humans to the surface ever. For instance if we find that:

  • Mars is sterile for Earth life - all the liquid water is either too cold or too salty. As of writing this, this is still a possibility.
  • Earth microbes will cause no confusion to scientific studies, and can't make Mars life extinct,
  • Mars life is unaffected by Earth life and either co-exists with it, or so outcompetes it that Earth life can't be established on Mars at all. That seems unlikely given the capablities of extremophiles on Earth, but again you can only find out by exploring
  • Mars life is identical to Earth life in all respects in the same habitat - as Zubrin and some others have said. Again this seems unlikely - surely there'd be significant divergence from Earth life and many species that wouldn't get there. After all, even with lake Vostok, cut off from the surface for a few million years, there's the possibility of enough divergence to be interesting and to require us to avoid contamination with surface life. But what if it is true?

Then, after enough study to make sure we understand the situation well and the consequences of introducing Earth life to Mars, we might get to a point where we decide we know enough to say it is safe to send humans there, much as we have already done for the Moon. We haven't done a thorough study of the Moon at all. Only know it from the ground in a few locations, and rather sketchy orbital surveys too, compared with Mars. Yet astrobiologists are confident that humans on the Moon don't need to take special planetary protection measures. It is possible that at some point we know enough to make the same decision about Mars.

However we don't know enough to make such a decision quite yet, I'd say. So we should leave open for now the other options such as for instance:

  • We decide that we have to keep humans away from Mars for the indefinite future, and perhaps cultivate Mars life there, or restore conditions for Mars life to flourish - this could be as amazing as having another exoplanet in our own solar system with it's different extraterrestrial life.
  • We decide to send humans there, but not yet. First we have to do a process of transforming Mars involving ecopoesis which keeps humans away in the early stages, and they go there later on.

There are many possible futures here. The main thing for now is to keep these options open, for as long as we don't know enough to make such decisions, which would be binding not just on us but our descendants and all future civilizations on Earth.

To follow this up further, you may be interested in the sections of my "Case for Moon First" starting with This approach doesn't mean that humans can never land on Mars ever

Also the later sections:

Here is my executive summary of the vision which I did before my most recent appearance on David Livingston's The Space Show.


Let's deal briefly with the ownership issue. I don't think it is a big deal.

The Outer Space Treaty says clearly that you own your own habitats that you construct in space, and since nowhere in space is worth living except in habitats, that deals with most of the ownership issues for space colonies.The case for ownership of minerals mined in space is far less clear. The US act mainly clarifies the US government's own domestic position - they made it illegal for anyone to sell moon rocks returned by Apollo, but have now made it clear that they will support their citizens if they try to sell materials mined from space. However they also say throughout the treaty that they will comply with all international obligations and treaties. What those will be is not known yet.

So it's not clear what the situation is there. However future law will surely somehow or other make it legal to return resources from space. There are many ideas for how to make it legal suggested by lawyers. The main sticking point here is that many say that the laws should somehow recognize that we go into space for the benefit of all humanity, as stated in the Outer Space Treaty, so the laws must be made fair for all countries, with many ideas about how that could be done. I don't think more needs to be said at this point. By the time Elon Musk or anyone else wants to set up colonies in space, I expect the legal issues will have got sorted out.

However planetary protection can't be dealt with in the same way. It's not just a legal issue. It is to do with whether or not one group of humans by sending microbes to Mars can rob the rest of humanity of the knowledge they could gain from a Mars without those microbes introduced to it. It's a conflict of freedoms we have here. The problem is that it is irreversible, and would change Mars for all future time.


Why not hold off from Mars surface for a while? Explore from orbit instead. And send humans to the Moon first, the obvious first place to test out our closed system habitats, safety systems, close to Earth. It may even have an economic case through tourism and through supply of volatiles to Low Earth Orbit, maybe even supply of precious metals to the Earth's surface eventually. And you can get back to Earth within two days in an emergency, can keep "lifeboats" attached to your habitats at all times, just as they do with the ISS, enough for all the crew to evacuate and return to Earth in an emergency, with provisions in the lifeboats sufficient to last the short two day journey back to Earth. You can also resupply with emergency equipment and provisions from Earth within two days - something that our space stations have had to do on many occasions in the past, emergency oxygen, and fixes for various equipment failures.

We may be able to get the transport costs from the Moon to LEO and back again down to almost zero by using Hoyt's cislunar transport system. This can be made with present day materials and weighs only 27 times the payload mass. It works by exploiting the position of the Moon higher in the Earth's gravitational well than LEO to power the transport of material back and forth, so long as more material is returned from the Moon to LEO than is sent there. It needs only minimal power to control the flow of the material from the surface (see Exporting materials from the Moon). It would be very hard to compete with that from Mars or almost anywhere else (though you can do similar tricks with spinning asteroids, spinning them down slowly meanwhile using the angular momentum to supply materials to Earth via a tether system).

There are many ways the Moon could be commercially viable, potentially, in the near future. I don't know if it is, but if anywhere in space can be, then the Moon seems our best bet. Dennis Wingo, Paul Spudis, David Schrunk et al and many others think it can be commercially viable.

  • Intellectual property rights and royalties of course, for any inventions and intellectual creations, According to Elon Musk, this is the only way that a Mars colony can pay for itself. I'm skeptical here, why would the flow be mainly one way, a space colony licensing its inventions to Earth more than the other way around, it seems improbable. For the detailed reasons see. Would a space colony survive with only exports of intellectual property to pay for imports?

    But if Robert Zubrin is right, his reasoning also applies to the Moon, you have the same labour shortage in a highly technological society, which he thinks should lead to creation of lots of valuable intellectual property in space and a flow of income to the space colonies from Earth.
  • Exports of the volatiles - initially supply of volatiles to cislunar space - depending on how easy they are to extract
  • Exports of precious metals - with the much lower delta v, then these just possibly might be commercially viable. Dennis Wingo thinks that the Moon may have valuable resources of platinum, gold etc. as a result of impacts of iron rich meteorites as well as the core of the giant impactor that created the south pole Aitken basin
  • Manufacture of computer chips that need high grade vacuum, readily available on the Moon, higher grade than anything easily achieved on Earth.
  • Export of solar power - solar panels should be easy to make on the lunar surface using in situ resources and the high vacuum - and some think there may be an economic case for exporting this solar power to Earth.
  • A place to build large particle accelerators - with no need for cooling or evacuation of the chambers.
  • Scientific research stations which would be funded from earth - hard to set up at the distance of Mars (though we may get them there eventually).
  • Astronomer's radio telescopes on the far side and passively cooled infrared telescopes and liquid mirror telescopes in craters - paid for by Earth - they may be built from Earth but probably need at least some human presence on the Moon.
  • Tourists as well. It's reasonably possible that you'll get wealthy tourists going for holidays on the Moon in the not so distant future. But who would go on a holiday to Mars, whether to the surface or to orbit or its moons, if it means you have to take two years or more out of your life to go there and back? Venus also seems too far away to have much tourist traffic in the near future. The Moon seems likely to get the lion's share of any space tourist industry beyond LEO in the near future, unless transport is speeded up hugely, and especially also given the much higher costs of a long mission to Mars or elsewhere in the solar system.

I haven't listed exports of Helium 3 for fusion here. Although it gets a lot of publicity, it's based on technology we don't have, and some experts think we will never have. Also, Crawford calculates (page 25) that manufacturing a square meter of solar panels on the lunar surface - which you can do by melting the indigenous silicon and using the high grade lunar vacuum to form panels in situ - would create as much power through solar power in seven years as you'd get from mining the same region for Helium 3 to a depth of three meters.

So, if mining for helium 3 is viable, this suggests that beaming solar power from the Moon back to Earth or to spacecraft in LEO would also be viable and a better business case than Helium 3. It may however be a useful byproduct of other mining operations on the Moon, for cryogenics, neutron detection, and MRI scanners, and possibly for fusion in the future. For details, see Case for Moon First - Helium 3 .

Also, I don't think colonization is the way to begin. That's like the early Antarctic explorers saying:

"Okay we've found this new continent, and there is nothing living here except penguins and seals, let's colonize Antarctica"

Space is so hostile for us and so dangerous and such a hard place to live, that it's far more inhospitable than Antarctica. Nowhere in space is nearly as suitable for colonization as Antarctica or the coldest driest deserts on Earth. You can breathe the air anywhere on Earth for starters, and it is hard to beat that.

I think the way ahead that's most likely to succeed is not colonization, but rather, settlement with industry, tourism, explorers, scientific bases like the ones in Antarctica. Take Antarctica as the model but with addition of permitted commercial exploitation of the resources which you can't do in Antarctica. Also the ESA idea of a lunar village is a good one - space is so much more dangerous than Antarctica, where at the least you can take breathable air for granted wherever you go. So I think we need the different space agencies to work together to start with, to have the habitats close together in one village rather than scattered over the surface, so that they can support each other, use common equipment and do this as an international venture. And see where that leads us.

Mars is not even needed long term if you have a vision of millions of people in space. The Moon has enough volatiles probably for a city of a million, enough water so each of those million people could have all the water in an entire lane of an Olympic swimming pool, maybe more. Huge caves that in the low Lunar gravity may be as large inside as an O'Neil colony, able to house millions of people in a single cave, so large that the city of Philadelphia could fit easily within the cave. We have radar data suggesting these caves exist, and can only find out for sure on the ground.

Then longer term, the asteroid belt alone has enough materials to build habitats for a trillion people, total land area a thousand times that of Earth. Here I'm not talking about hollowed out asteroids or covering asteroids and dwarf planets with a shell, but using asteroid materials to make new habitats in space. The mass requirements and the technology requirements are just about identical to those for Mars, except for the regolith shielding - which you need on Mars as well, using bulldozers - in space colonies you'd use them too with mass drivers. But space colonies have the advantage you can set up any gravitational level inside, through spinning the habitat, any amount of illumination using mirrors, and can position them anywhere you like in the solar system too. You'd start off making them using materials from the Moon and from asteroids that do close flybys of Earth with low delta v needed for capture of the materials in the Earth Moon system - simultaneously eliminating the risk of them ever hitting Earth by mining them away to nothing, and making a habitat that is within easy reach of Earth, perhaps located in cislunar space.

Mars is not the only place to go to. As well as the Moon and the asteroid belt there's Callisto as well, outermost of the large moons of Jupiter, and the only one of them outside its lethal radiation belts, is within two years journey of Earth via type II Hohmann transfer. It's an icy body, and preliminary study suggests that though there is a global ocean below the surface, it is completely insulated from the surface. This needs to be checked with robotic missions first, but it probably has no planetary protection issues. Venus cloud colonies also have a lot to recommend them, surprisingly, with protection from the acid using teflon and other plastics far easier than protection that has to hold in atmosphere against a vacuum with outwards pressure of tons per square meter. There are advocates for Mercury colonization too.


Our imaginations can soar indeed with ideas like that. I was so glad that Elon Musk chose to include these wider visions and not just focus on Mars. His technology can be of great benefit for human and robotic exploration of the entire solar system. But let's leave the places of most interest to the search for life - Mars, Europa, Enceladus and perhaps Ceres and Vesta - for exploration via robots and telerobotics for now, and leave consideration of whether to send humans to the surface of these places to a later date once we know enough to make a properly informed decision.


This answer is partly based on material in my Case for Moon First. It also uses material from my previous articles:


The kindle book may be useful if you want it formatted as a book, which you can read on your kindle, and also on most major smartphones, tablets and computers, using the free kindle reading app.


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


Robert Walker's posts - on Quora

And on Science20

Robert Walker's posts on Science20


And I have many other booklets on my kindle bookshelf

My kindle books author's page on amazon

My kindle books author's page on amazon