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I wrote this soon after ExoMars's successful launch to Mars, 2015. Hurray! In the program about the mission, before and during the launch, the presenters talked about the care they take to sterilize the lander of microbes to protect Mars. And indeed, kudos to all the space faring countries, and the planetary protection officers, for doing this. But in the same program they talked about ideas to send humans to Mars, talking about all its benefits. For some reason it never seems to occur to anyone to ask if humans can be sterilized in the same way as robots. There is nothing unusual about this - it's the same for programs from NASA, or programs about Mars on UK television, and anywhere. The topic of planetary protection just seems to get forgotten as soon as presenters discuss humans, even if they were talking about it for robots only a few minutes previously.

Once you start to think about it, though, it is a tough question, is it not? How would you sterilize a human occupied spaceship - with its food, the astronauts' digestive tracts, skin, lungs, air, water? How could you remove all its microbes and still leave a functioning spaceship with live humans inside? It's surely clear that you could never do that, to the same level of sterilization as a robot. So, can you continue to protect Mars from Earth microbes if you send humans there?

Scientists do discuss this, in papers, workshops etc, but these questions rarely, or never, seem to be brought to the public attention.

Elon Musk hopes to land a hundred colonist hopefuls at a time as soon as the early 2030s. NASA also proposes its "Road Map to Mars" which could see human "boots on Mars" in the near future.

Every year Humans2Mars holds a big conference on the topic. And of course the Mars Society has numerous simulated Mars missions on Earth. So does the ESA, and Russia. The main question on everyone's lips seems to be, how soon can we do it?

There could be another perspective here. I think there are many reasons to stop and think a bit before doing it in such a rush.

If we "win the exobiology lottery" with the discovery of new forms of life on Mars, it would revolutionize biology. And who knows what other benefits could come from an example of another form of biology? Potentially it could also revolutionize medicine, agriculture, nanotechnology and many other fields. Think what it would mean to find just a few extraterrestrial creatures, even tiny microbes, on Mars. You can explore this further in my Will We Meet ET Microbes On Mars? Why We Should Care Deeply About Them - Like Tigers

So, what happens if your top priority is no longer to land humans on Mars as soon as possible? What happens if you make it your priority to protect the planet for science? You begin to see things a bit differently.

The best way to protect Mars from Earth life is not to send humans to the Mars surface at all. That way, the only risk is from our robots, which can be sterilized to whatever levels are required. Sending humans to land on the surface is more exciting perhaps, but also more expensive and dangerous too. What we can do is to send humans to Mars orbit.

I'd like to argue strongly that the best thing to do at our present state of knowledge of Mars is to send humans to ORBIT AROUND MARS, and NOT TO THE SURFACE.

Before getting down to the details, let's quote from "When Biospheres Collide", Michael Meltzer's history of NASA planetary protection programs - as I think it's a great way of motivating this planetary protection centric approach to space exploration.

It's a similar idea for telerobotic exploration of Mars. With humans in orbit around Mars, their robot avatars on the surface are their and our collective sense organs, so we can all follow along, as they explore the surface. They can to explore both sides of the planet, on the sunny side, every day - and control robots all over Mars.

Perhaps we may some day have a scene like this, with astronauts in orbit around Mars looking out on the planet, and below, there are rovers on the planet controlled by them like this

The main thing I'd like to suggest here is that this decision is too important to be done by scientists alone. Just as we have plenty of people bringing the idea of colonization to public attention - I think we need the issues of planetary protection brought to public attention as well and discussed. That's the reason for writing these articles and kindle booklets.

I come to this as someone who loves science fiction, and is keen on human spaceflight, but who also loves science. If the two clash, as may happen here - well for me there is no question at all which has priority of those two.

By putting forward strong points of view myself I hope to stimulate debate and help make sure we make the right decisions in the future. Whatever those may be.

I hope that you may find the ideas here stimulating. Perhaps it may get you thinking about, and debating topics that are seldom explored in discussions of human spaceflight, in public. We may need to make decisions in the near future, perhaps as soon as the next decade or two. I think it is high time this got aired more widely and talked about publicly. Yes many of us have heard people passionately arguing that we must send humans to Mars. Perhaps it might be interesting to hear from someone who thinks just as passionately that we shouldn't do it quite yet. Almost anywhere else is fine, the Moon, asteroids, space habs in orbit around Earth or other planets, Jupiter's outermost moon Callisto even. But let's go slowly with Mars, Europa and Enceladus!

WOULD HUMANS ON THE SURFACE REALLY BE AN ADVANTAGE?

First, if it is optimal for planetary protection to keep humans away from the surface, well I'd argue, we simply shouldn't do it, because planetary protection should have priority.

However, you often hear people say that humans on the surface can get so much more done than robots. That would seem to make sense. Is it worth relaxing planetary protection a bit, in order to get this extra capability that humans have for exploring it?

Well, actually, our experience of robots exploring in space is limited, and it may not be a good guide to what we will be able to do in the future. We have not yet explored the Moon in this way - not since Lunakhod in the 1970s.

With Mars we are severely handicapped, not so much by the distance, but by the bandwidth. Everything has to go through the "Deep space network" through giant radio telescopes and the signals are faint. It's a bit like trying to control the rovers over one of the old dial up modems. But worse, in a way - there is so much demand for the telescopes, and such limited bandwidth from Mars also, that the rover controllers can only connect to them about once a day.

Imagine trying to control a rover over a dial up connection which you can only use once a day, and you get a good picture of how it works. Our rovers could be as far away as the Kuiper belt, beyond Pluto, and it would hardly make any difference.

What difference would it make if we had broadband communications with Mars? It's hard to say. If we could send the commands to Mars every hour or less (communication delay is 6 to 42 minutes for the round trip), then we might well be able to do as much in less than half a year as we can currently do in a decade. It took ten years for Opportunity to travel as far as Lunakhod did in a few months with 1970s technology. Perhaps it could have been as fast as Lunakhod with broadband - the light speed delay compensated for by our modern technology advances since the 1970s.

Our rovers also have some level of autonomy, and will get better at it. They are surely already easier to control than Lunakhod.

So, I don't think it is even the case that we need telerobotic exploration of Mars with humans in orbit. Maybe we can do it all with robots. Especially if we use Artificial Real Time - a technique from gaming.

The idea is to build up a simulation of the Mars site in 3D in your computer on Earth, complete with simulated physics, and then much of the time you just drive around the simulation in real time, continually updating your model with information from Mars as it comes in. That could speed up the time it gets from a to b on Mars which is a lot of what takes up so much time with our explorations. Especially if the rovers also have even more autonomy and ability to recover from accidents and stop if you try to drive them into a boulder etc.

But human exploration is more exciting and can probably do the job faster, if also more expensively.

The only study I know of came to the conclusion that humans in orbit like this could do as much surface exploration as three teams on the ground , for the cost of a single mission to orbit. You save a lot by not needing to suit up, and by leaving your robot avatars in situ, so you can start work immediately where you left off the previous day - no matter where it is on Mars by then.

It also has less danger for the humans (you don't have the risks of landing on Mars, or of using spacesuits on the surface, and it is easier to return to Earth in case of problems). That way you use the best talents of both humans and robots in collaboration to find out about Mars.

If we want to compromise between the human and the robotic approaches, I think this is the best way to do it for now - to send robots to the surface, and send humans to orbit first, and no further, until we have a chance to explore the surface more carefully.

NO NEED FOR HUMANS FOR DRILLING

This is something humans on Mars advocates often say, that we have to send humans to Mars, as it is the only way to drill below the surface. This argument is most compelling if you think life on Mars only exists deep down, at depths of many meters or kilometers. I'll come to that later. There's a variety of views here, as in the last decade, a number of scientists have started to think that there's a strong possibility of life in the top couple of centimeters, or in cracks in rocks and similar habitats right on the surface. But let's look at the drilling question first.

Humans might not actually be that good at drilling on Mars. On the Moon in their clumsy spacesuits, the astronauts struggled to get a simple core drilled from the surface, even falling over in one early attempt. They often struggled with things that would be easy on Earth, for instance it was almost impossible to pick things up from the surface - they had to use tongs.

And as for deeper drilling - on Mars as on the Moon, there'd be no water to lubricate the drilling rig. If you tried, the water would just evaporate.

It turns out that in these near vacuum conditions, you have to use different methods for drilling. One of the best ways to do it may be to use a robotic self hammering mole.

In theory this can drill down for kilometers into the Mars crust, studies show. The first practical test of this will probably be with the Mars insight lander, which will use a robotic mole to drill to a depth of about eight meters (originally planned for 2016 but now delayed).

ExoMars uses a different solution, a form of rotary drill, but will also be able to drill down 2 meters in its search for life.

So - it doesn't seem humans are essential here. Probably humans could learn from the lunar astronauts and find easier ways to do it. But this is certainly something that can also be done via telerobotics from orbit. And we can drill as deep as we like, to find deep subsurface samples on Mars.

WHAT WE COULD FIND ON MARS

There are many ideas for how life may have started on our planet - but those simpler forms of life are all gone now, as far as we know. Most think they were made extinct by DNA based life when it evolved.

Those simpler forms of life may still exist on Mars, and maybe are still alive to this day. Or life there may have evolved in some radically different direction from Earth life, or it might even have had a new origin of life from scratch, with no connection at all with the evolutionary tree of Earth life. It is a discovery of this magnitude which we could potentially find on Mars.

It is thought that Mars was as habitable as Earth in the early solar system. If early life on Mars evolved far enough to be reasonably hardy and versatile, and if there are habitats for it still present on Mars, then it is probably still there today.

EXAMPLE OF LAKE VOSTOCK - WHY WE CAN'T PROTECT MARS WITH A COMPROMISE

This may seem rather a black and white position that I'm presenting, the idea that we shouldn't land humans on Mars at all until we know what we are doing. Could we not compromise with enthusiasts who are so keen to land humans there? Could they not land for a short visit of a year perhaps, so long as they take special precautions to reduce the risk? Just to maintain the human interest of a mission to the surface?

But how can you protect Mars with a compromise solution? It sounds a bit like saying you can import diseased plants, but only for an hour on Monday afternoons. That would be less risky than permitting import any hour and any day of the week. But why run the risk at all, if it can be avoided?

It's rare that you need to prevent contamination by microbes. But it does happen, even on Earth. Take the example of Lake Vostock in Antarctica.

The Russians drilling into Lake Vostock would love to to explore this unique lake and find out what kind of life is there, and whether it has hydrothermal vents (as some think), and if so, what communities of life live around them. It has been separated from the surface probably for millions of years.

You might ask why they don't drill down and drop a sub into the lake, such as is used for exploring the deep sea bed. But they can't do that, because we don't yet have the technology to sterilize even a robotic submarine sufficiently.

They waited a decade before doing anything, with the drilling stopped a few meters from the water, while they searched for a solution. Finally, they drilled into it momentarily, enough to cause a geyser of water to rush up 40 to 80 meters before it froze over, and sampled this instead. It's rather similar to plans to sample the geysers of Enceladus. They believe that this action had no risk of contaminating the lake.

And that's it. They still haven't sent a submarine down, and have no plans to do so, as far as I know.

PROBLEM WITH STERILIZING ROBOTS AND HUMANS

Actually we can sterilize robots 100%. It's easy, just heat your robot to a few hundred degrees °C, or zap it with lots of ionizing radiation, and there will soon be no life left at all. The problem is, that this will also destroy the delicate electronic equipment - the instruments we want to use, the computer chips, the navigation system and so on. So the problem is, to find a way to sterilize our robots that doesn't also destroy them.

All life depends on organics, and robots can be made of metals. So if you could design the robot so that it doesn't use organics in its construction, and then find some way to remove all the organics, that would do the trick, and would be a perfect solution.

But we don't know a way to do this yet. The ESA is exploring one solution that is close to being able to achieve this, using supercritical CO₂ snow, but it's still work in progress.

There are many other methods - heat treatment, low pressure hydrogen peroxide vapour, ionizing radiation, etc. But they all have the same drawback, that none of them are yet 100% effective. Either that or they destroy the robot.

It's the same with humans. But it's a harder problem to solve for us, as we are made up of organics like microbes. We have no hint of a method so far that could sterilize humans of microbes without killing us.

I think it's important to realize that humans are not the problem here, but rather the microbes that always come with us.

MARS THOUGHT TO BE EASIER TO STERILIZE A MISSION FOR

So when we can't use them in lake Vostock, why can we send robots to Mars, and why are we even considering sending humans to Mars?

Well the reason is that lake Vostock, as a liquid water environment is especially challenging.

Most of Mars is thought to be far less hospitable to life than lake Vostock, and indeed less hospitable than anywhere on Earth, even our driest deserts. Indeed it used to be thought that the surface of Mars was likely to be completely sterile. Even as recently as 2008, that was the accepted view of almost everyone. About the only voice saying anything different was Gilbert Levin who is to this day reasonably certain that his labeled release experiment already found life on Mars in the 1970s.

The view prior to 2008 was that water is impossible on the Mars surface. They said this with what seemed to be good reasoning at the time.

Water boils at 0 °C over most of Mars due to the low atmospheric pressure for a similar reason that mountaineers climbing Mount Everest can never make a piping hot cup of tea). On Mars even at the lowest depths of the Hellas Basin, tea would boil at just a few degrees centigrade. Indeed, it's so close to boiling that any water would evaporate quickly, faster than clothes drying on a sunny day in the Sahara desert. Even ice would evaporate into the atmosphere pretty quickly. For this reason, back then they thought there was no water or ice in the equatorial region down to depths of hundreds of meters, perhaps kilometers.

So, they thought, stable ice only occurs on the surface in polar regions where it is extremely cold.

You do get a form of ice in the equatorial regions, frosts, present for 200 days of the year, photographed by Viking. This is very temporary though. It forms when the night atmosphere gets so cold that CO₂ freezes out as dry ice, taking some water ice with it, which then remains behind briefly as the dry ice evaporates in the morning sunshine. But most researchers (except Gilbert Levin again) thought it was impossible for life to exploit this frost before it evaporates, because it never turns liquid

.They did think that there could be liquid water on Mars kilometers down. The Mars crust gets warmer with depth, just as it does on Earth, and deep down water could be trapped from evaporating to the surface so could be liquid.

They also thought that there could be liquid water even close to the surface, perhaps in caves, if heated by geothermal hot spots. But if so it would have to be trapped from the surface, otherwise it would evaporate.

HUMAN MISSIONS TO THE SURFACE OF A STERILE OR NEARLY STERILE MARS

With this picture of Mars, humans could land on the surface, and they would not risk contaminating these deep subsurface habitats so long as they were careful, especially when drilling.

The spores from their habitat would be bound to spread a bit in the global dust storms that happen occasionally (the dust season comes every two years in the Southern summer, and sometimes covers the whole planet as happened in 2001). This is an issue that Carl Sagan raised - that a spore imbedded in a dust grain would be protected from the UV light by the iron oxides in the dust, and could be carried at hundreds of miles an hour in the winds. But this wouldn't matter as the spores would never find their way down to these subsurface habitats.

So back then before 2008, there were detailed plans for human landings on Mars. Because life can't be totally disproved by these arguments, there was a requirement to return a few samples from Mars first, in the "Safe on Mars" report, to check that there really is no life there, before sending humans there.

But they expected a "green to go" result from this sample return, and then after that, to just send humans there to study on the surface. The advantage of sending humans is that we are great at making on the spot decisions, which is not so easy for robots. Even things like driving - so far our rovers on Mars haven't been able to drive around on the surface by themselves.

WHY IT IS NOW SO MUCH MORE COMPLICATED AFTER THE PHOENIX LANDER

That all changed dramatically with the discoveries of the Phoenix lander in 2008. The first of its discoveries that got everyone rethinking their ideas about Mars was an accident - when what looked like droplets of liquid formed on its legs. They couldn't analyse them directly sadly, they were just in the wrong place to do that. But one hypothesis is that salt thrown up by its landing on Mars ended up on its legs then deliquesced, took up water from the atmosphere. The droplets, or whatever they were, grew, sometimes merged together, and eventually disappeared abruptly (probably fell off the leg) and then never formed again in the same place.

Droplets on the legs of the Phoenix Mars rover, 2009, Credit: NASA/JPL-Caltech/University of Arizona/Max Planck Institute.
(click for animation)

Then as well as that, through isotope measurements of the CO₂ in the atmosphere, they proved that, Mars is geologically active in the recent past (continually producing CO₂) - so presumably will be again in the future too, and also, that the oxygen from the CO₂ has exchanged chemically with some liquid on the surface. - almost certainly water. They couldn't tell if this happens only sporadically, after meteorite strikes, or volcanic eruptions forming temporary lakes - or is present all the time. But one way or another it suggested liquid water, which perhaps life could use, on the surface of present day Mars.

This lead researches to the question: "Could salts take up enough water from the atmosphere to create habitats for life on the surface of Mars?"

NEW IDEAS FOR MARS HABITATS

It turns out that the atmosphere on Mars, though it has hardly any water vapour in it, nevertheless reaches hundred percent relative humidity at night. That's because of the temperature changes. Here on the West coast of Scotland, next to the sea, where I'm writing this, the air is nearly always very damp due to the sea air. and due to the low temperatures, especially in winter. But if you could make the air here as hot as in the Sahara desert, it would be very dry, even with the same amount of water vapour in the air.

On Mars, the air and surface temperatures plunge by 80 °C or more at night frequently. This makes the air suddenly very humid, 100% relative humidity - and is the reason it can have these frosts in the equatorial regions. So the researchers asked if salt deposits on Mars - there are lots of those - could take up this night time humidity. And turns out they can. They have to experiment with unusual mixtures of chemicals for Earth as nearly all the salts there are highly oxygenated. For instance instead of the sodium and potassium chloride of table salt, you have chlorates or perchlorates. Anyway it turned out that yes, they can deliquesce, though often at temperatures far too low for life.

Then the DLR team in Germany studied some lichens from high mountain ridges in Antarctica - which have to live in an environment with no liquid water at any point in their growth cycle. They manage this feat by using humidity in the atmosphere. They wondered if they could do the same feat on Mars. They also have several special pigments that protect them from UV light, which is much stronger in these situations than elsewhere on Earth. They also hide in cracks in the rock, so the partial shade + pigments gives them the conditions they need to photosynthesize even with the high levels of UV light.

Anyway the outcome of those researches was surprising - yes they did manage to survive in a Mars simulation chamber, could handle the vacuum conditions, the plunges of temperature at night to temperatures cold enough for dry ice. Also when in partial shade similarly to their Antarctic habit, they could survive the high levels of ultraviolet light, and the complete lack of any liquid water at all. And what's more they actually metabolized and photosynthesized, so were actually still growing as well. Remarkable. And the fungal component of the lichen managed okay even with no oxygen - it got the low levels of oxygen it needed from the algae component.

They also found that some extremely hardy single cell cyanobacteria could survive in the same conditions.

CONFIRMATION OF LIQUID SALTY WATER ON MARS

Then we also got indirect confirmation of liquid water on Mars. First the Recurrent Slope Lineae - these are dark streaks that form in spring, spread down the slope and widen through the summer, and fade away in winter. Unlike other streaks and seasonal features on Mars, they form on sun facing slopes, and only when local temperatures reach above 0 °C. This is far too warm for them to be anything to do with dry ice. Also there is no correlation at all with winds or dust storms. With the slow seasonal growth also - the only explanation that made much sense was that it has to be a feature caused by water mixed with salts, which flows down the slopes. The dark patches are not "damp patches" but some other effect on the dust grains of the surface. But thought to be caused by thin films of salty liquid flowing beneath. As to where the water comes from, the jury is out, main hypotheses are deliquescing salts at the head of the streaks, or else, from below through geothermal hot spots, possibly all the way from the kilometers deep hydrosphere if it exists, or there could be reservoirs of ice just below the surface, accumulated in the distant past when Mars had ice in these regions.

Anyway - sadly the spacecraft that took these photos of them can only take photographs in early afternoon as it is in an eccentric orbit that takes it close to the sunny side of Mars at that time. So it can't photograph them in early morning which is when the liquid water is likely to flow. It was a big challenge to find out much more. But then last year, some scientists managed to tease out the signal of hydrated salts - which correlate with the streaks, and this hydrated salts signal disappears when they fade away. They didn't have the resolution to prove that this signal comes from the streaks themselves, but because of this correlation, and all the other things known about the streaks, it is thought to be reasonably conclusive evidence that there is liquid water there at times.

Then there were a couple of other developments, just last year. First, a team lead by Nilton Renno have found that in a Mars simulation chamber, liquid water can form very quickly on salt / ice interfaces - his widely reported "swimming pools for bacteria on Mars". So this is not deliquescence, as the water doesn't come from the atmosphere, but rather from the ice. It happens much more quickly than it does from deliquescence. These habitats could occur anywhere on Mars where there is both salt and ice potentially in contact with each other. Basically anywhere in the higher latitudes of Mars.

Then as well, Curiosity found out that it has been driving just a couple of cms above a layer of liquid water in the sands of Mars. It can tell by variations in humidity of the air as it drives. This layer is thought to be due to deliquescing salts again. The liquid dries out as the day progresses, then forming again each morning. This layer is warm enough for life some of the time - but too salty. At other times the water is not quite so extremely salty so life could just about manage - but is too cold. So most think it can't be habitable. But Nilton Renno, who is in charge of the Curiosity REM "weather station" on Mars has suggested that life, because it can modify local climate, and create its own microclimates, could perhaps find a way to survive in this layer.

ARE ANY OF THESE LIQUID WATER LAYERS HABITABLE?

That leads in to the big question here. We now know for sure that there is liquid water on Mars, even in equatorial regions - the Curiosity measurement is particularly conclusive. But is any of it habitable for Earth life? And if not, could any of it be habitable for Mars life - which might have evolved to be able to take advantage of liquid water at lower temperatures than Earth life, for instance?

Nobody knows .But there are so many proposed habitats for life on Mars, that it will probably be a long time, some decades at least, before we know for sure, except of course if we find a confirmed habitat, which would prove that they exist.

There are many other proposals over and above the ones I just described. One of the most intriguing that is seldom mentioned - is the possibility that the flow like features in Richardson crater could be caused by trapped liquid water at 0 °C heated by the solid state greenhouse effect, like similar liquid layers in Antarctica. Another intriguing suggestion, just mentioned briefly in a paper, is an idea for life in salt pillars using micropores in the salt, which trap water even at rather low relative humidities. This is another process we can observe on Earth, in the dry Atacama desert. For a survey of most of the proposed habitats up to 2015, see my Are There Habitats For Life On Mars? - Salty Seeps, Clear Ice Greenhouses, Ice Fumaroles, Dune Bioreactors,....

NO LONGER EASY TO FIND OUT IF MARS IS SAFE FOR HUMANS OR VICE VERSA

With the earlier rather simple idea of the Mars surface, you could hope to get a decent idea from just a few samples. Though even back in 2002 they said that an in situ search would work better, if we had equipment light enough to send to Mars to do it.

Nowadays we do have those instruments now as a result of technology advances and miniaturization in the last decade. Since the 2002 survey already said an in situ search would be better, I'm pretty sure that if it was redone they would say that an in situ search was the way to go, especially with these new ideas for habitats on Mars. The problem is that present day life is hard to detect, and organics are expected on Mars anyway from meteorite impacts, so if you find organics on Mars it doesn't follow that you have found life, or a life habitat. Also in such harsh conditions there may be seemingly identical habitats with some inhabited and others uninhabited. You can only check for this with in situ searches.

IMPLICATIONS FOR "ROAD MAP TO MARS"

As you can imagine, this is exciting news for astrobiology. It now really begins to seem possible that we might have a chance to encounter present day "micromartians".

NASA and COSPAR seem confident that it will be okay, but I don't see a clear basis for this confidence myself at this early stage.

The main difference I think is that they seem to be still working with the idea that the surface of Mars is almost completely sterile, as they talk about the need to drill to find life. So. I suppose it depends how impressed you are by the new ideas for habitats on Mars.

I look at those ideas and think "Wow, there are now possibilities for habitats almost anywhere on Mars, even in equatorial regions". Nilton Renno is an example of a researcher who has this attitude. (author of the long survey paper "Water and Brines on Mars: Current Evidence and Implications for MSL" and many other papers on the potential for liquid water on present day Mars).

Other researchers however, look at these proposals with skepticism and expect that perhaps all of them will be disproved and life on Mars shown to be possible only underground.

If you think habitats on Mars could be common and widespread, then the problem of planetary protection may begin to become far more acute and immediate.

I know many people are really keen to go to Mars, in the States. Here in Europe we don't have that at all, not the fervor of anticipation that you have in the States as I understand it. There are large conferences in the States, speeches and congressional hearings all devoted to finding ways to send a human mission to the Mars surface. We don't have any of that here in Europe.

Anyway, why Mars? Most of the solar system is completely free for human exploration, with a few natural restrictions just as you have on Earth.

The Moon is category II meaning you can do anything, so long as you document it. But there are ideas to set up the equivalent of "national parks" - vulnerable areas that need some care. Perhaps associated with ice at the poles or in caves, and the historical landing sites. That is not yet legislation and is "work in progress".

And same also for Callisto (moon of Jupiter outside its intense radiation belts that some think might be a place to settle), Mercury, and many places in the solar system are not a planetary protection issue at all.

There are three top priorities for planetary protection: Mars, Europa and Enceladus. These are the ones that need especial care. .

The US, ESA, China, Russia etc all have the right under the OST, and indeed the obligation to prevent "harmful contamination" of celestial bodies by their own citizens, or anyone using rockets manufactured by their citizens, or who launch from their territory. All countries that have signed the OST have the same obligation - if it interferes with the scientific study of Mars.

There is no planetary protection issue at all with going to the Moon or asteroids.

If a private company wants to go to an asteroid, and take enormous risks, nobody will object, except perhaps the families of the astronauts. This is not a measure to prevent people taking risks.

It's only because it impacts on others that these restrictions are in place in the Outer Space Treaty, as interpreted by COSPAR. It's like laws to prevent introduction of rats and rabbits to remote islands, or to prevent importation of diseased plants. It just makes sense; why would we want to bring Earth life to Mars before we have a chance to study it?

CURRENT IDEAS FOR MARS

So, the current ideas are that we can still send humans to Mars, but that it has to be done on the basis of keeping the contamination restricted as far as possible to the region around the human landing site. They would then send sterilized rovers to explore further afield, perhaps controlled by telepresence.

What is possible here is a matter of further research. We'd want to know more about surface conditions on Mars. We need to understand whether spores can be spread in the dust and how easily, and so forth.

BIOLOGICALLY REVERSIBLE EXPLORATION

Chris McKay suggested in the past that we should explore Mars in a biologically reversible way. The idea is that if we find interesting life on Mars, we can remove all our contamination from the planet and leave it for the Martians instead - so that we can study the biology there etc. Maybe even get to restore the early Mars climate.

That would be an exciting prospect seems to me. It's like having our own exoplanet, with its distinct biology, in our own solar system. The nearest terrestrial planet like that, other than Mars, may be light years away. Depending on future technological progress, it might be centuries before we have a similar opportunity - or if life is rare in our galaxy, maybe even millions of years.

WITH THE ROAD MAP TO MARS, BIOLOGICALLY REVERSIBLE EXPLORATION IS IMPOSSIBLE

If we land humans on Mars, with present understanding, they think it would be possible to keep the contamination restricted to the landing site for long enough to do a scientific study of the rest of Mars. But the result would not be biologically reversible. This would mean we no longer have this future opportunity to engineer Mars for the micromartians.

Note that if we do change Mars by introducing Earth life - that is a binary thing, either you introduce life or you don't, no half measures. It doesn't seem possible that you could introduce life to just a quarter of Mars say. Not if it is biologically irreversible.

IT WOULD BE A NEW GEOLOGICAL ERA ON MARS

This means it would be nothing short of a new era on Mars. Maybe it needs a new name.You have the earliest Noachian period of high meteorite bombardment and seas, the Hesperian period of volcanic activity and huge floods, the Amazonian period, as it is now, dry with some liquid water, a bit volcanic activity and occasional floods - and then we'd need a new name, maybe call it the Anthropocene again, as on Earth - of a Mars with Earth life on it, introduced by humans. After all on Earth geological epochs are named according to the prominent biology on the planet. So why not on Mars?

From then on for all future time, our civilization and all future civilizations on Earth would never have the opportunity to study the Amazonian period, with whatever unique lifeforms it might have.

And - it is well possible that Earth life could make Amazonian period Mars life extinct. After all, according to most theories of the origins of life, DNA life made its precursors on Earth, whatever they were, extinct. And later forms of DNA life made many earlier forms extinct. So it's certainly possible for one form of life to make another extinct over an entire planet.

In the case of life exchanged between two planets which has never had the opportunity to make the trip before, then it seems possible this could happen in either direction.

It would be only small consolation if we get the opportunity to study this life before it goes extinct. Whether it takes a decade, or a century, or even a thousand years for the Earth life to reach every habitat on Mars, surely it would do so eventually.

Imagine what it would be like if we end up in that situation, where we find some unique form of life on Mars, perhaps for instance RNA based life using ribozymes instead of ribosomes, cells only 50 nm in diameter. Or even multicellular life, some unusual lichen, maybe again with minute 50 nm cells, but at that point we know we have already introduced Earth life to Mars in an irreversible way and that this newly discovered life will go extinct on Mars, with nothing we can do to prevent it? That the only thing we can do is to do our best to study it as quickly as possible before it goes extinct?

THROWING AWAY A TICKET FOR A LOTTERY WITH A PRIZE OF INCALCULABLE VALUE

I've no idea what the chance is of something as wonderful as this on Mars, or the chance that Earth life would destroy it. Probably nobody can know until we get a chance to explore Mars thoroughly.

But it's what I've been calling a "superpositive outcome" in my posts here - something so positive that even if it is low probability, we must not deny our future selves and other future civilizations of this opportunity.

You often hear about people who buy a ticket for a state lottery - and then find they have won, only to then find out that they have lost the ticket.

Introducing Earth life to Mars before we know what is there, and then finding some vulnerable early life or non DNA life there after it's too late - that's like throwing away a ticket for a lottery with an incalculably valuable prize, just before the prize is drawn.

It would be too late after that for some "good samaritan" to return the ticket to us. It's lost for good.

CRASHING ON MARS

So that takes us to the main issue. Can we land humans on the Mars surface without greatly increasing the risk of contaminating it?

I know that the COSPAR committee and the NASA planetary protection office, and many experts are optimistic that we can find a way.

I am speaking only for myself here. And the aim is to get people thinking about this and debating it. Not saying that you have to accept what I say!

But I just can't see it myself, yet. I haven't seen any proposals or plans that seem watertight and convincing, to the point where you look at the plan and say "Yes, I see, this method will certainly protect Mars, I get it now!".

The various plans may look good on paper, but they lead to many questions we can't answer.

POSSIBLE DISCOVERIES THAT MIGHT MAKE HUMAN LANDINGS ALMOST INCONCEIVABLE EVEN FOR NASA AND COSPAR

To get an idea of why I say that we can't guarantee that humans will be able to land on Mars quite yet - let's try a thought experiment.

Suppose we find some interesting but feeble form of life on Mars before the proposed human landing, e.g. a precursor of Earth life, which got made extinct on Earth by more modern DNA based life.

Our first opportunity may be with Exomars, as the first rover sent to Mars since Viking sensitive enough to have a chance of this.

So suppose it finds this life. I know most think this is unlikely, that we would find it so soon, but it's not impossible, if you think Gilbert Levin's labeled release already found life on Mars, or if you think that life in biofilms could exploit the layer Curiosity found, or think that equatorial life on Mars could use the 100% night time humidity.

After a discovery like that - could COSPAR continue to support human landings to the surface of Mars and say they are not an issue for planetary protection?

I think surely not, if Mars life was as interesting, and also as vulnerable as this.

But who can say this can't happen. There have been many surprising discoveries on Mars. Perhaps we will find something like this and it will wake everyone up! Stranger things have happened in science.

So - how can anyone say, yet, that we are confident that COSPAR will find suitable requirements to permit humans to land on the Mars surface?

And particularly how can they possibly hope to learn enough to be able to approve a human landing without first studying Mars very thoroughly to see if some such biology or habitat exists there, somewhere on the planet?

That's why I said in my Space Show guest appearance that I can't see them having enough information to approve a human mission to the Mars surface until they have first explored it thoroughly with robots, or with humans in orbit exploring it telerobotically.

If you have planetary protection policies at all, there must be a possibility of prohibiting humans landing, just as you would prohibit tourists, however wealthy and technically capable, from exploring Lake Vostock in a sub, or bathyscaphe.

WHY IT MAY BE HARD TO KEEP A HUMAN HAB BIOLOGICALLY ISOLATED FROM THE SURFACE

There are many things you can do to try to keep the hab isolated, with all the Earth microbes inside.

Yes they can clean the outside of spacesuits. Yes they can use suitports to reduce the amount of dust that gets into the habitat and life that escapes - though it still leaks a cubic foot of air every time it is used (that's a special type of spacesuit that is attached to the spaceship via its back so you crawl into the suit and then detach it eliminating the need for an airlock, and losing only a cubic foot of air to the Mars atmosphere each time you use it).

Yes, it's true, that though spacesuits leak all the time, the conditions on Mars are very harsh so long as they land in the dry equatorial regions. Yes, surely, most spores released from the spacesuit will be sterilized by the strong UV light in the only slightly filtered Mars sunlight.

But - first spores are very hardy. They just need to fall into the shadow of a boulder to be completely protected from UV light. They can also be protected by less than a millimeter of dust.

Some spores are especially hardy - if you have enough spores, a few will survive long periods of time in Mars conditions before they succumb. There will be some viable spores left after hours or even days of direct sunlight.

Or they could fall behind a boulder during a night time EVA - or just fall to the ground in the shadow of the astronaut.

So long as a spore can get into a permanent shadow, it will remain there, unharmed until picked up by the global dust storms, maybe a few years later. The solar storms and cosmic radiation on Mars are not strong enough to sterilize spores completely over short time periods of a few years.

PERCHLORATES IN THE DUST STORMS

You might think that perchlorates in the dust would help sterilize the spores. But perchlorates are more hazardous and active at higher temperatures, such as room temperature or temperature of the human body. At colder temperatures they are much easier to tolerate. And as well as that there are some microbes that use perchlorates as a food source.

Studies of spores in perchlorate rich Martian analog soils have shown that they survive fine, so long as they are protected from UV lighht. If anyone knows of a similar study for the Mars dust,do say. Seems no reason why the perchlorates in the dust should be a problem perticularly.

GROUND TRUTH FROM MARS TO CHECK UP ON OUR PLANETARY PROTECTION MEASURES

So far we've done all our planetary protection on the basis of models and theories and experiments on Earth. We have no data at all on how well the measures have worked in practice. We don't know how many spores were still on Viking or any of our spacecraft when they got to mars.

That's one of the things that I think would be good to check on the surface. A couple of spacecraft would be of special interest here.

REVERSIBLE CONTAMINATION, AND WHAT TO DO IF IT IS CONTAMINATED ALREADY?

Though most think it is unlikely we have contaminated Mars irreversibly with Earth life, there is no way to say for sure at this stage.

It's a probability thing, Carl Sagan initially aimed for a 1 in1000 chance of contaminating Mars during the "exploration phase" which is how we thought about it then. We have had less stringent planetary protection measures, Mars has seemed more hostile to life, yet recently perhaps not as hostile as expected. Also had a few lapses, especially the Mars climate orbiter.

So there is a chance we have contaminated Mars though no way to estimate the probability based on the very limited information we have about Mars so far.

We almost certainly have many dormant states of microbes, and spores on Mars, just sitting there doing nothing. The big question is, has any life started to reproduce yet, or might it in the future?

That's where Chris McKay's idea of reversible contamination comes in. And I think this needs study on the surface to see what got there. The scientists involved think that the spores are largely confined to the rovers themselves. It's different from a human occupied spacecraft - with lots of flakes of skin, dust, water being drunk and spilled, air full of spores. With a sterilized spacecraft the only spores are the ones on the craft itself, and the population reduced by the ionizing radiation and UV light on the journey to Mars and on the surface. Of course it is shielded from UV light during the actual transit and half the spacecraft is in permanent shadow on the surface if a stationary lander - while rover moves around so pretty much all its surface would be exposed to UV light.

I think that needs study on the surface. Chris McKay has at least spoken about the possibility of reversing this contamination by our rovers.

To do that, you'd be best using 100% clean rovers or you could make the situation worse. I see no reason why we can't have 100% clean spacecraft eventually, in theory anyway, if we can somehow find a way to completely remove all organics from the spacecraft - we can use them to remove our present generation of dirty spacecraft from Mars, and clean up the dust and tracks. I mean long job but in future may be much easier than for us now, with semi-autonomous rovers - I suppose depends how much there is by way of spores in the dust.

It's a challenge, because they didn't design the guidelines for Mars around Chris McKay's idea. Instead it was based around Sagan's idea of an exploration period of intensive biological research for maybe 40 yeras - before relaxing the standards - which never happened.

Now COSPAR no longer think in terms of an exploration phase but indefinite protection, until we find out enough to change policy, for unmanned missions. Which makes it even more puzzling to me that they are considering reducing the planetary protection requirements for manned missions.

If we have contaminated Mars already, then it may not be the end of any chance of studying the previous life on Mars.

First, it could be just a small patch, if we are very lucky. Say, a single patch around Phoenix - or a few localized to our landers. If so maybe we can sterilize them and reverse it anyway.

If not, there's a chance it is a lifeform that plays nicely with whatever is on Mars - or that even if it has caused problems already - that there is something interesting on Mars still that won't be made extinct by whatever we introduced already by mistake.

If we find we have irreversibly contaminated Mars already - the last thing we should do is to introduce more life. I think that would be a big wakeup shock for scientists if that has happened and would lead to much stronger planetary protection measures in future. After all after introducing rabbits to Australia, the last thing you want to do is to introduce cane toads (which did happen and became a nuisance there also).

REVERSIBLE CONTAMINATION STANDARD FOR NEW DESTINATIONS

I think that for missions to new locations like Europa and Enceladus, we should design the requirements on basis of reversible contamination from the get go - the easiest way to do that for those missions is to do flybys of the geysers to start with - and for any landers, make sure that any part with a chance of contacting water that's potentially habitable (deep enough to be protected from ionizing radiation for Europa) - that they are 100% sterile, or if they land on ice only with no chance of contacting water - that they have some method of sterilizing themselves at the end of mission, e.g. an ionizing radiation source with shielding which is removed at end of mission (some method that happens automatically) and then sterilizes it continuously for the following thousands of years so even when finally subducted into the ocean it would have no spores on it. With Europa then Jupiter's ionizing radiation would do for end of mission sterilization but only if you can guarantee it can't go deep enough to be protected from it in event of a hard landing.

Parts of the surface may be long term stable for billions of years for Enceladus so may not need extra protection. Probably all of the surface of Europa is resurfaced on quite short timescales geologically. And if it has those penitentes in its equatorial regions, and other rough features - then a crashed lander falling amongst them could be protected from ionizing radiation somewhat depending how deep they are - if it also has crevasses or some such - maybe deep below the surface. Or if it crashes through soft ice.

see ice blades threaten Europa lander. I'm thinking of doing another article about the planetary protection issues for a Europa lander at some point.

PROBLEM OF TRASH HEAPS AROUND THE HABS

Then - as well as that - how likely is it that in practice the Mars astronauts can keep their habs so contained and insulated from the surface of Mars as expected in the guidelines. Equipment has glitches, fails sometimes, has to be repaired. They would have bad air and problems in their recycling from time to time.

Sometimes they would need to vent the air. Sometimes food would go off and they wouldn't want to keep that in the habitat. Eventually after many uses, their clothes would get torn, and need to be replaced. They would need to replace equipment. Seed trays in the greenhouses would break, or the outer covering need to be replaced. They would receive shipments that need to be unpacked, and then they have to dispose of the packaging. From time to time there would be accidents on the surface with the spacesuits breached.

I just can't see it working that they just pile up all their refuse and no longer functioning equipment, spacesuits that don't work any more, broken seed trays etc inside the habitat for years on end. And there's no way they'd send all that back into orbit either.

And as well as that, how could you ensure that they follow these guidelines? Especially if we get Elon Musk's hundred colonists per trip landing on Mars - who ensures that they all follow the guidelines? What can you do remotely from Earth if someone just decides not to follow the precautions because they are not interested in exobiology and just don't see the point? Just chuck some useless bit of machinery out of their airlock, or some food that's smelly, or even a crew mates offensively dirty socks? Even perhaps just in a fit of temper?

I think we need experience of human settlements on the Moon first. If we do that, I wouldn't be surprised if we find we get a refuse tip builds up outside every habitat, eventually dwarfing it and needing to be buried or otherwise disposed of. At least if it is like the ISS, that's what would happen. Of the tons they dispose of every year from the ISS to burn up in the Earth's atmosphere - only some of that is because they haven't yet achieved perfect closed systems growing their food and generating all their own oxygen. There's lots of other refuse on top of that.

CRASH OF A HUMAN OCCUPIED SHIP

But - apart from that, the thing that makes it really very hard to see how a surface trip could be approved is the problem of a crash of a human occupied ship on Mars.

Unless, that is, they make it a requirement that all ships sent to Mars with humans must be proven to be 100% reliable. But how could that be enforced? How could we achieve 100% reliable landings with near future technology?

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. It is especially tricky with its 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.

Once you hit the atmosphere you are totally committed and can't back away again if the landing starts to go wrong. But you can't just use parachutes either. It is surely the most difficult place to land, in the entire inner solar system, and maybe in the solar system altogether. Venus and Earth have more gravity, making it harder to get to orbit. But they are easier places to land than Mars because they have such thick atmospheres.

I know this brings back painful memories for many, and sorry about that. But we can't avoid this subject here.

It doesn't prove that a spacecraft is safe, to land it say four times on Mars with cargo first. Even with a 50/50 chance of a crash, you can get four perfect landings in succession with probability of 1 in 16. And even learning on the job, using telemetry from previous landings, still, can you really and truly say it can't possibly crash?

I think the safety level needed for planetary protection should be far higher than for humans who are prepared to take risks. Perhaps many would be colonists would be willing to take on a 1 in 100 risk of a crash, around the levels of the estimated risk for the space shuttle after the redesign after the two crashes.

But for planetary protection - the usual aim is a 1 in 10,000 risk of contaminating a planet per mission. With ideas of a super positive outcome, I would say that even that is not low enough myself - but that much is already accepted internationally as a consensus from COSPAR.

A HUMAN LANDING AT LEAST INCREASES THE RISK OF CONTAMINATION

It seems pretty clear that the only way to approve a human landing is to permit an increased risk of contamination of Mars by Earth life to greater than the notional 1 in 10,000. And bearing in mind the possibility of a crash, perhaps it's a greatly increased risk.

Why do that? NASA especially, with science as such an important part of their remit - why accept this increased risk of contaminating Mars in its roadmap? And why do it in such a way that if you do find interesting and vulnerable early life on Mars, there is no future possibility of reversing the contamination? When you can do it using telerobots instead?

ISSUES FOR HUMAN ORBITER MISSIONS

You have to sterilize unmanned orbiters, which are far less of a contamination risk than a human landing. as they stay in orbit are still required to be kept clean, though to lower standards than landers, due to possibility of impact:

You'd think that that would also apply to human orbiters. I suggest ballistic transfer for those, as an insertion burn can easily end up with impact on the surface for a mistimed burn - so the impact probability must be significant for human orbital missions also - and no way you could clean it even to the level suggested there.

Also the reason they can suggest that for orbiters is because of the idea that the spacecraft could burn up almost completely in the atmosphere - all the delicate parts, hopefully enough to ensure that it doesn't contaminate the surface with impact.

With the much larger human occupied orbiters, then surely much would remain on impact, so I think those have to have trajectories that just can't end up with a surface impact. With ballistic transfer you could gradually lower the orbit with an ion thruster with no need for an insertion burn which is why I'm really keen that we use it for human orbiters to Mars - just a suggestion of course - would need expert attention to check if it is feasible.

NO URGENT NEED FOR A BACKUP FOR ASTEROID IMPACTS

There is no great rush to colonize Mars. It will still be there a thousand years from now, or a hundred thousand years from now. We don't need it as a backup either as I've covered in previous posts. So just to touch on it again briefly.

First, if you have watched some of the science fiction movies, perhaps you think we need a backup for asteroids that could boil our seas perhaps, or turn over the land. Like one of the animations done for the Discovery Channel.

We can check up to see if such huge impacts are possible by looking at the cratering record. There are indeed many big craters on Mars, the Moon, Mercury, the moons of Mars, even on Earth, but they all date back to the late heavy bombardment not long after the formation of our Moon when our solar system was still settling down, and a few hundred million years after it. There haven't been any impacts that big for well over three billion years.

There are larger objects than that - but it seems Jupiter protects us. Simulations lead to the same conclusion. Large objects beyond Jupiter would not start up in an Earth crossing orbit - very unlikely due to the tiny size of Earth and becasue they would be in an orbit in a different plane, again almost certainly. So they will pass close enough to Jupiter to be disrupted or deflected within a few orbits.

We do have a risk of impact with a smaller 10 km asteroid impact. However, though these do make many species extinct, I think no reason to think of them as human extinction events.

They are also exceedingly rare , the risk of a 10 km asteroid impact is far lower than most imagine; they happen once every 100 million years. It's random of course, so we can't say that because the last one happened 66 million years ago, that we are safe for another 34 million years. But there is only a one in a million chance per century. And now that we have mapped all the 10 km asteroids between Jupiter and the sun, the risk is 1 in ten million for the next century with at least a half year warning, and probably a lot more, since it would have to approach from way beyond Jupiter or we'd have spotted it already.

It's 99.99999% certain we don't get hit by a giant asteroid this century and we should get lots of warning on the remote chance we do. It's certainly possible to be hit by smaller asteroids but that's not the main topic here. It's rare, far rarer than volcanoes, eruptions and tsunamis, but with the unusual feature that with enough information we can predict an asteroid impact to the minute and also with enough warning, deflect it rather easily.

But anyway even if we were hit - we are amongst the most adapatable of all creatures - not innately, but with just the minimum of technology we are.

We are so adaptable, we can live almost anywhere, from the Arctic to the Sahara, tropical rainforests, coral atolls, or up in the highest mountains. That's with pre-industrial technology. We'd surely be amongst the 1% that survive a mass extinction, along with turtles, crocodiles, alligators, flying dinosaurs (the birds), small mammals, dawn redwoods, pine trees etc.

We are lucky to live in a quiet area of the galaxy, around a star in a solar system that is in a quiet phase, with a sun that is stable and not the sort that has giant solar flares. We don't need a backup, not for at least many millions of years into the future.

So I don't think we need to rush into space to escape Earth. We have millions of years to create a backup if we need one.

PROTECTING EARTH

Instead we have to protect Earth. Go into space to defend against asteroids yes. For a fraction of the cost needed just to get started on a colonization attempt - just half a billion dollars can launch a space telescope to find nearly all of the most hazardous of the smaller asteroids within 6.5 years. Five billion dollars would pretty much retire the risk from asteroid impacts - unless we find one headed our way, of course, in which case we can deflect it.

The thing is that the speed change needed to deflect it is less, the sooner you can find it. With just one hour of warning, you'd need over 6,000 km / hour to miss by the radius of Earth, not very practical. But If you have ten years of warning, then you can deflect it to miss Earth with a change in speed of 100 meters / hour. Conventional explosives, or just kinetic impact, or even "gravity tractors" could do it.

Then most asteroids will do many flybys before they hit, as Earth is such a tiny target. This involves passing through a gravitational keyhole in space, of a few hundred meters in diameter, in order to hit Earth next time around. With, say, a decade before the flyby, you just need to change its velocity by a few tens of meters a year to miss the keyhole. This change is so small you could achieve it by methods such as painting a dark asteroid white to change the heating effects of sunlight on it. (as they spin around and release the heat from the daytime side into the night, this deflects the asteroid - it's a tiny effect, but significant enough that it has to be taken account of in asteroid orbit predictions).

NO NEED TO GO TO MARS TO ESCAPE GAMMA RAY BURSTS OR SUPERNOVAE OR BOILING OCEANS

Then on the exceedingly remote chance of, say, a nearby gamma ray burst, some humans would survive these events through technology. After all that's the whole point in the backup, to build a highly technological habitat that could survive anything, even a supernova or gamma ray burst.

But Mars is no more protected from cosmic disasters than Earth. Indeed it is less protected.

The easiest place to survive these also is on Earth, with the extra protection of our atmosphere equivalent to ten meters of water to protect against radiation, and with air you can breathe outside the habitat. It's a far better place to ride out a supernova or gamma ray burst than Mars.

On Earth we can also go deep below the surface in nuclear submarines, or deep in mines. At any time there will be a few people in these places anyway just by chance. The event would directly affect only one side of Earth also, in this remote chance. Many humans would surely survive to try to start rebuilding. And where would it be best to rebuild after such an event? On Earth of course. There's no point in heading off to Mars to rebuild, when Earth is here.

We have millions of years before we need to worry about changes in our solar system, or movement of our sun through the galaxy, leading to increased levels of risk over what we have now. We have half a billion or a billion years before the oceans boil. Technology might solve that also - perhaps just through putting lots of solar shades in orbit around Earth, and there are also ways we could change Earth's orbit to move it further out, on those long timescales.

Who knows what the issues there will be and what technology we have if we can survive for even thousands of years.

So, I don't see a backup as an urgent priority right now, and don't think Mars would be the best place for it either. A free flying space colony, if we can ever make those self contained and closed system, would be far more robust and independent.

COLONIZATION COULD BRING ITS OWN PROBLEMS - RISKING EARTH RATHER THAN SAVING IT

Also space colonies would be the most technological on ever attempted. Even more technological than the ideas for subsea colonization.

Any future issues that arise through technology are as likely to start in space colonies as anywhere. E.g. who would be the early adopters of nanotechnology? And of the most advanced 3D printers? Space colonists obviously. If you think artificial intelligence is an issue (I don't think it is myself) - again space colonists have more need of computers than anyone else.

If technology is what you are afraid of, it doesn't seem, to me, to make a whole lot of sense to try to escape from those dangers by setting up an even more technological society in space.

And they wouldn't be isolated from Earth. Soon we'd have spacecraft able to get there in weeks, maybe faster, if you had colonies. Probably will anyway within a decade or two even without them.

And they have technology they could use to directly threaten the Earth e.g. block out the sun from us, or divert asteroids to hit us, or any number of ways. If we have millions in space, then at some point then they would militarize space for sure, if done rapidly and with everyone going into space including North Korea or anyone that has space aspirations. You can't just keep the colonies for the "good guys" indefinitely with millions in space, you'll get "bad guys", whoever you think the bad guys are.

In case that seems a black picture - that's a worst case future, not what I think will happen.

SPACE SETTLEMENT AND COLONIZATION AS NEUTRAL

But there is no rush to get into space. I see space colonization as neutral. And our technological problems come mainly from the pace of change. We have managed to cope, more or less, with a huge number of technological inventions of the last hundred years. Including

Now imagine if all of those things had been invented in just one decade between 1900 and 1910, instead of a hundred years? I'm not sure humans would even survive that, and almost surely much of our planet would be devastated before people realized the many issues with these new inventions.

These things are all neutral, and we can learn to use them well and cope with the undesirable effects.

Similarly with space settlement and colonization. I think it is neutral, it can be very good indeed, help save the Earth, move destructive industries into space, help preserve ecosystems, produce space solar power, and there are many ways space settlement can help the Earth.

It could be of great benefit to Earth and also lead to many discoveries in space. Could lead to revolutions in biology also if we find exobiology on another planet or moon.

But - there is no great rush, and especially, no rush to colonize Mars as soon as possible.

MANY OTHER PLACES TO COLONIZE

There are many other places to colonize - the lunar caves for instance. But most of all, using materials from the asteroid belt - this is an insight of the 1970s. There is enough material in the asteroid belt to make space habitats with total surface area a thousand times that of Earth.

That's why they designed the Stanford Torus and the O' Neil cylinder in the 1970s. The future of space colonization may well be in free space. Maybe we are too "planet centric" having evolved on a planetary surface.

Also there's a lot to be said for the idea that it is better to learn about how to support a space settlement closer to Earth. We've sort of "settled" the low earth orbit with Skylab, MIR and the ISS. By settlement here I mean more or less permanent occupation, not bringing up your kids there and expanding populations - I'd call that colonization.

The next step surely is the Moon. Only two days back to Earth in an emergency, and easy to resupply also in an emergency. We've been exploring for decades with humans able to get back to Earth in just a few hours. It's too soon to get to the situation where they may be only able to get back in over a year (waiting for next transit opportunity to Earth).

Even for exploration not settlement, then the Moon is the obvious place to go first. It's also a lot more interesting than it was thought to be some years back.

If you want more of a challenge, try the far side of the Moon with only indirect communication with Earth via lunar satellites, and the Earth no longer visible in the sky. It'd an ideal spot for radio telescopes, shielded from Earth by the Moon, so we may well get the lunar equivalents of Aceribo in craters on the far side of the Moon. And before that, the simpler long wave telescopes consisting of just wires spread over the surface.

COLONIZATION DOESN'T ALWAYS WORK

Space colonization advocates often paint pictures of the Europeans arriving in America or spreading across the West. But those were colonizations of regions that already supported humans. And colonization, even on Earth, of areas already habitable for humans, doesn't always work.

The Vikings attempted to colonize North America five centuries earlier, and archaeologists have unearthed traces of their settlements in L'Anse aux Meadows in Canada. But they only stayed their for a short period of time, then they gave up.

Later on, many of those living in Scotland, made themselves bankrupt through the grand Darien scheme to start a new colony called Caledonia in Panama, which failed, with most of the colonists dying and ships bringing a few of them back home. It's failure lead to loss of an estimated one quarter of Scotland's liquid assets at the time and was one of the main reasons Scotland lost its independence and had to accept unification with England in the early eighteenth century.

Before we can build self sustaining colonies in space, I think we'll first achieve the far far simpler task of floating sea cities. These could use only the sea water and air as resources, similar to habs on Mars using only the CO2 and the ice, with no need for fishing, or any other use of Earth's natural resources. They'd be very eco-friendly.

Surely if we ever do achieve the ability to set up space colonies, then sea colonies like this will be easy, and the ability to build these sustainably will come first. For more on this, see my Can You Suggest A Second Earth Apart From Mars

SUGGESTION - HUMANS IN MARS ORBIT WITH AVATARS ON THE SURFACE AS FINAL DESTINATION FOR NOW

So anyway that's how I see it. And I think the "road map to Mars" should have Mars orbit as the final destination for humans, with avatars on the surface, not humans on the surface of Mars. At least until we get a chance to study Mars properly from orbit.

And though Mars is undoubtedly far more hostile to biology than lake Vostock in Antarctica, I don't think we have anything like enough understanding to be sure yet that it is okay according to planetary protection to send humans there.

Especially when you consider the wide range of possible habitats on Mars, and you consider the possibility of some very vulnerable early form of life, maybe some type of life that was driven to extinction by DNA life on Earth long ago.

I also think we should continue to explore Mars in a biologically reversible fashion. And that when there are alternative mission proposals such as to send humans to the surface or controlling robots on the surface by telepresence - that planetary protection should be our priority and guiding light. For now at least, until we understand Mars better.

FUTURE CLASHES

I can see this potentially leading to a clash some time down the road. What is going to happen if Elon Musk wants to send 100 people to Mars in the early 2030s?

I have no idea what he thinks about planetary protection or whether he values the search for exobiology as he has never discussed it, as far as I know. He may value the search for life highly. But what if someone wants to do this and doesn't want to wait for us to learn enough from Mars to satisfy COSPAR?

If he planned to drill into lake Vostock in Antarctica and to put a submarine into the lake to explore it with human tourists in the submarine, he would be denied permission. Why not the same for Mars then?

Even if it is not certain that it would contaminate Mars with Earth life, if it greatly increases the risk over robotic missions, why should this be okay? Don't the rest of us matter, who want to study Mars in its pristine state? Or future generations, and civilizations, do they not matter?

CHANGING POLICY FOR COSPAR

COSPAR policy does change of course. After Viking they decided that robots don't need to be sterilized so much because the surface is so hostile to life.

But since 2008, the pendulum has swung the other way a bit. The surface has turned out to be more hospitable than was expected, not less so.

So, unless for some reason we decide Mars is no longer of interest to exobiology - which seems unlikely - surely our planetary protection measures should be getting more stringent for Mars, not less so, to match this new vision of an increasingly habitable Mars?

If so, it is hard to see how permitting humans to land on Mars could be justified by new knowledge in the same way that the relaxation of requirements was justified after Viking.

It seems that the justification is rather the other way around. That we want to send humans to Mars, but the only way to do that is to relax the policies, so they have to be relaxed. This is the wrong way round to do things, seems to me, if planetary protection has the priority.

SO COULD WE EVER SEND HUMANS TO MARS IF IT IS DECLARED "OFF LIMITS" FOR MICROBES?

So, what happens if after new scientific discoveries from Mars, some future COSPAR meeting decides to declare Mars off limit for Earth microbes indefinitely? Perhaps because we find some fragile and interesting early form of life on Mars, as I suggested as a possibility?

First I think it's important to realize that it's not really humans that Mars needs protection from, only our microbes and the microbes in our habs, and perhaps some very hardy multicellular lifeforms - lichens, maybe even tardigrades if there is any oxygen rich habitat or microhabitat on Mars. But humans as such are not really a problem, if only we could be separated from our microbes.

We could grow trees on Mars if we grow them from a sterilized seed in sterile hydroponics type environments supplied with all the chemicals they need for growth.

The problem is that we can't sterilize humans. Maybe some ETs can sterilize themselves, if their biology permits it, but not us, not at present anyway.

The human body has about the same number of non human microbes as human cells. We need at least some of this life to survive, as it is the only way we can digest our food.

In principle you could imagine somehow exchanging all the microbes we have with ones that are incapable of surviving below temperatures of say 30 °C.

That would be enough to make it safe for humans to land on Mars. But how could that be done, in practice? How could you sterilize the human skin, lungs, digestive track, sinuses, eyes, etc etc of all microbes without killing us as well?

It's hard enough for robots. It seems impossible for humans. At least not with present day technology. In a science fiction story you could let the characters do it with nanites - reproducing nanoscale machines, but we don't have anything like those yet.

You could try the same idea as for a tree - to grow a human from an embryo on Mars in an artificial womb. And introduce only microbes that you know are unable to survive on Mars. Maybe with warm cuddly avatar parents so that it has a reasonably normal upbringing, interacting with its real parents via telepresence.

But apart from the many ethical issues, we don't have anything like this technology yet. And any harmful microbe free humans on Mars would not be able to return to the planet ever, if they leave it, in case they bring Earth microbes back to Mars.

So - no - if Mars was off limits for our microbes, I don't see how we could get around it to visit it ourselves in person in the near future. At least not if they can walk on the surface reasonably normally.

Except - with impervious fully recycling spacesuits which also can't be damaged at all in a crash on Mars. You can invent those too for science fiction stories. But we don't have those either, not yet anyway.

LANDING ON MARS IN A GIANT STEEL BALL

There is one way you could do it. Put the human inside a giant steel ball with a small hollow inside. Seal it up with enough food and oxygen to last for a while on Mars. It has to be totally impossible for it to breach in event of a hard landing, even at kilometers per second. But that I think would be possible (engineers might like to comment).

But not sure I see the point. Technically they walk on Mars, but they only get to experience the Mars gravity, don't see anything and can't get out.

Perhaps eventually though we find a way to send astronauts to the surface in transparent bubbles in some 100% reliable way and they float about or have wheels that drive them over the surface.

MEANWHILE, TELEPRESENCE

This gives you enhanced vision, you can even make the skies blue if you like. Colours of rocks are just as on Earth. You can touch things, or see them through binocular vision in 3D. Also 3D sound as well. It could be so immersive it really feels as if you are on the surface. Probably more so than if you were actually there, in a clumsy spacesuit In reality you are walking around in a Virtuix Omni type treadmill in your orbital settlement, with artificial gravity set to Mars levels, generated perhaps through a tether spin. But to you it feels as if you are really there.

It's a spectacular orbit also, the likely orbit for an early telerobotic mission.

I see this and similar missions as a far better end goal for the "Road Map to Mars". If you like you can plant a flag on Mars. Even send a sterilized humanoid avatar to plant it in some ceremony to celebrate your achievement. We already have quite a few flags on Mars on our rovers there.

And let's leave ideas for humans on the surface until we know a bit more about what is there. Then we can decide whether it is the right thing to do, and whether or not it will impact on future generations and civilizations.

NEW GEOLOGICAL ERA ON MARS

If there are habitats for life on Mars, it will certainly create a new geological era there, to introduce Earth life there - unless we find Earth life is there already. Some think that is possible. If that's the situation then we should find that out fairly soon. If so we can then act on knowledge and understanding of the situation.

If there is Earth life already on Mars, we need to study it carefully first to understand it. It would probably have evolved separately in the different conditions there, at least for millions and probably for billions of years. And only some of the many Earth lifeforms could get there.

The most interesting situation for exobiology though is that we find early life, or most interesting of all, some alternative biochemistry. If that was proved, I think everyone would agree we need to take great caution.

It's the order that we do things that matters here. It would be tragic if we sent humans to the Mars surface and found out only too late that we shouldn't have done this, and that this impacts on a fragile and vulnerable form of early life on Mars.

HUMAN MISTAKES

And humans can make mistakes. Our universe is not arranged in such a way as to make sure we can never make mistakes. Even the brightest people, informed by the best knowledge of their time, can make mistakes. Look at the blunders we've made on Earth. Sometimes intentionally, introducing rabbits to Australia, not understanding the consequences. And sometimes by mistake, rats getting onto remote islands with no intention behind it at all. These were clever people as well. They seem foolish to us in retrospect, but wouldn't have been thought so at the time.

In my view, with the possibility of a superpositive outcome, we simply must not let it happen, that we make a mistake like this with Mars. Or with Europa or Enceladus - the three places of supreme interest for exobiology in our solar system. There is nowhere else to go, we have no spare Mars planets to experiment with - within light years in all directions at least.

NOT SAYING WE CAN NEVER SEND HUMANS TO MARS

The main point here is that we don't have a planetary protection strategy in place unless it has the ability to protect Mars if future scientific research shows it is too valuable and vulnerable to permit human landings quite yet.

I think there's a good chance that this is what will happen and that's why I predict in the show that it might not be permitted to land humans there for the foreseeable future. But we all know how predictions from even fifteen years ago often are well off the mark. So I'm not at all saying that this is what will happen, it is just my own best guess right now. It's because I've been impressed by all the new potential habitats for life found on Mars and anticipate that at least one or two of those will turn out to be habitable to Earth life, so making Mars surface far more vulnerable than most assume.

Whether this is true or not, my main point is that the best way is to explore Mars telerobotically only until we find out more. Because it would be an awful anticlimax and a huge mistake if we find out we have contaminated Mars with Earth life after the event. It is different if you know it is going to happen and have made an informed decision that it is okay, with global agreement and a good understanding of what is on Mars already.

But, in my view, we must not let it happen by accident. And the best way to make sure we don't introduce Earth life by mistake is to explore Mars telerobotically.

SO WHAT DO YOU THINK?

The main reason for writing this is to stimulate debate on these topics, and to help make sure the debate is done with an informed background.

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Can We Risk Microbes from Human Crashes On Mars?

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