It is hard enough to sterilize the robots we send to Mars to search for life. How can we expect to do the same for humans? It's at least a major challenge. I've argued that to start with we should send humans to Mars orbit only. They would explore the surface by telerobotics. That way you use the best talents of both humans and robots in collaboration. It's surely the best way to protect the planet from Earth life.

The best possible outcome here could be the most significant revolution in biology, perhaps since the first discovery of microbes and living cells. A "super positive outcome".

We are surrounded by the products of biology, and are biological beings ourselves. New insights into biology could lead to new developments in medicine, agriculture, nanotechnology, create new products for use in industry, and lead to new understanding of the origins of life and the possibility of life on other planets.

How can we reduce the probability of such a discovery just in order to have humans stand on the Mars surface a few years sooner?

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, and 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, for instance, hardy dormant states or spores - and if able to live in some habitat 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 the enthusiasts who are so keen to land humans there? Let them land, for a short visit of a year perhaps, with precautions to reduce the risk?

But how can you protect Mars with a compromise solution? It's a bit like protecting a country from Dutch Elm disease with a compromise that lets you import diseased timber, 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?

This situation for Mars is not unique. We have a similar situation on Earth right now with Lake Vostock in Antarctica, kilometers below the ice. This is probably the most oxygenated water on Earth (it gets there in a kind of conveyer belt of ice, slowly driving bubbles of air into the lake under huge pressure).

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 robotic sub into the lake, such as is used for exploring the deep sea bed. But they can't explore it because we don't yet have the technology needed to sterilize even a robotic submarine sufficiently. So they just don't do it.

They waited a decade before doing anything, 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

Acutally we can sterilize humans and robots, but there's a downside.

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 destory the robot.

So, we can't yet sterilize our robots 100%.

It's the same with humans. We are more delicate than robots, and there is no hint of a method so farthat 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 THAN LAKE VOSTOCK

So why can we send robots to Mars, and why are we even considering sending humans to Mars? When we can't send them on what would seem far less challenging expeditions on Earth?

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

While most of Mars is thought to be far less hospitable to life 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 labelled 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 it was thought to be impossible for life to exploit this frost before it evaporates, because it never turns liquid (Gilbert Levin was perhaps the only one who thought that there might be some way for life to use it, but he didnt' have a detailed model to explain how it would happen).

They thought that there could be liquid water on Mars kilometers down. Like Earth, the Mars crust gets warmer with depth, and water down there could be trapped from evaporating to the surface so could be liquid. And they thought that there could be liquid water even close to the surface, if heated by geothermal hot spots. But if so it would have to be trapped from the surface, otherwise it would evaporate.

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 an idea 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. With this 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 equpiment light enough to send to Mars to do it (we do have those instruments now as a result of technology advances and miniaturization in the last decade).

But they expected a "green to go" result 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. Two of its most important discoveries that got everyone rethinking their ideas about Mars is that first, that 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. 

And as well as that, through isotope measurements of the CO₂ in the atmosphere, they proved that, first 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.

All this got the researchers looking carefully at ideas of deliquescing salts. 

NEW IDEAS FOR MARS HABITATS

Could salts on the surface of Mars take water from the atmosphere? 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. 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 liqud 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 

IMPLICATIONS FOR "ROAD MAP TO MARS"

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

But I think it might mean we need to modify plans for human landings on Mars. NASA and COSPAR seem confident that it will be okay, but I don't see how they can be so sure at this early stage.

I know many people are really keen to go to Mars, in the States. Here in the UK we don't have that at all, not the fevour of anticipation of a human landing on Mars that you have in the States as I understand it.

Anyway - most of the solar system is completely free to human exploration. There may be a few 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".

For asteroids particularly - you can go anywhere. 

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.

There is no legislation to prevent you taking risks wth your own life. If a private company wants to go to an asteroid, and take enormous risks, nobody will object, except perhaps the families of the astronauts. It's only becaues it impacts on others that these restrictions are in place in the Outer Space Treaty, as interpreted by COSPAR.

CURRENT IDEAS FOR MARS

You can read about current proposals and research towards human missions and planetary protection here - the 2015 workshop with many videos. And there are more documents available for download from the Planetary Protection office.

And listen to Cassie Connely talking about it here on the Space Show.

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, as a probability. Nor do I know what the chance is that introducing Earth life would destroy it.

I don't think anyone knows enough to calculate this either. 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 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. Going to Mars, introducing Earth life before we know what is there, and then finding some vulnerable early life or non DNA life there after it's too late, is like throwing away a ticket for a lottery with an incalculably valuable prize, before the prize is drawn.

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 don't see how we can.

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. It's going to be hard to do that because we may only explore the equatorial region and that not very much either.

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.

Then - 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 as vulnerable as this.

So - how can anyone say that we are confident humans will be able to land on the Mars surface already? And paricularly how can they possibly approve a human landing without first studying it carefully to see if some such biology or habitat exists there?

That's why I say 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 future possibility of prohibiting humans landing just as you would prohibit touritst, however wealthy, from exploring Lake Vostock in a sub, or bathyscope.

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

First of all - I don't see how a human hab on Mars can be kept isolated from the surface anyway, even with the harsh conditions there.

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 (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 completely dry equatorial regions. So 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 if covered by less than a millimeter of dust.

Some spores are especially hardy - in a large population of these hardy spores, a few can survive long periods of time in Mars conditions before they succumb, for hours or even days of direct sunlight, especially if partly shielded by other spores.

Or they could fall behind a boulder during a night time EVA from the habitat - or fall into a shadow on the ground when the astronaut himself or herself is also in shadow. 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.

PROBLEM OF REFUSE HEAPS AROUND THE HABS

Then - as well as that - I'm not at all convinced that humans on Mars 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 too thick for a lunar module type landing. 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.

How can you be sure you won't get this sort of thing happening?

Debris from Columbia - broken into tiny pieces by the crash.

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

Twice the space shuttle failed. Each time, they thought that the risk of this happening was tiny .

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 consenus 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?

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.

Most of those who say we need a backup say it is because of giant asteroid impacts as one of the main threats. But 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 ths 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 astroid impact to the minute and also with enough warning, deflect it rather easily.

Humans anyway 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.

And our Earth is also a much more complex one than the world of the dinosaurs with its one giant tropical continent. We have land masses all the way to the South pole and most of the way to the North pole and at almost all latitudes in between. We would definitely find habitats that humans could survive in during and after a giant impact on the present day Earth.

As for the larger asteroid impacts you see in some movies including an animation done for the Discovery Channel - there have been no impacts that big in the inner solar system for well over three billion years, on any of the planets with a long geological record. There are 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.

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.

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. 

Find one headed for us a decade in advance and it's easy to deflect. 

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).

NOR ANY NEED TO GO TO MARS TO ESCAPE GAMMA RAY BURSTS OR SUPERNOVAE OR BOILING OCEANS

Gamma ray bursts, or nearby supernovae also would not make us all extinct. For one thing there are probably no candidate supernovae close enough to have harmful effects on Earth and gamma ray bursts are extraordinarily rare and highly directional.

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. But the easiest place to survive these also is on Earth. A hab that could protect from a gamma ray burst or supernova on Mars would protect humans far more easily on Earth, with our atmosphere equivalent to ten meters of water to protect against radiation, and air you can breathe outside the habitat.

And we can 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. 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, leaing 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.

Meanwhile our top priority surely has to be to preserve the Earth.

NO NEED FOR HUMANS FOR DRILLING

This is something colonization 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.

However, humans wouldn't 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 the attempt. 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 a completely different method for drilling. The best way to do it may be to use a robotic self hammering mole. At least that's the one that mission planners have preferred so far.

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). Or with ExoMars which will use a similar method to drill down 2 meters in its search for life.

This is certainly something that can be done via telerobotics from orbit.

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 of 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

•  Jet planes
• Cruise missiles
• Nuclear weapons
• Biological warfare
• Chemical warfare
• Tanks
• Submarines
• ICBMs
• Can cut down forests acres at a time with great ease
• Build huge roads
• Kill animals easily. 
• Sonar to spot fish and whales
• Infared vision
• Radar 
• Personal computers - well computers at all at first
• Cell phones
• The list goes on and on

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.

I don't think the answer is to stop inventing things and slow down innovation.

Rather, it shows that we can adjust if we are given time to do so.

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, andthere 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 luanr 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.

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 thnk 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 for 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 micobes.

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. And every time you eat food eat a warm soup of microbes to help digest it.

Or remove all the stomach microbes, and use drip feeding.

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

But for now, by far the easiest way to do this is via telepresence.

This gives you enhanced vision, you can even make the skies blue if you like. Colours of rocks just as on Earth. Touch things, 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. 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.

And everything streamed back to Earth so we can all have this same experience.

I see that 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 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.

I wrote this after my recent guest appearance on the SpaceShow hosted by David Livingston. You can hear it here:

See also Cassie Conley's guest appearance, which presents the standpoint of NASA and COSPAR.

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.

What do you think about these ideas? Do say in the comments.

SEE ALSO

• TheSpaceShow Broadcast 2663 Dr. Catharine (Cassie) Conley: Topics: Planetary protection
• TheSpaceShow Broadcast 2660 Robert Walker: Topics: Planetary protection and human spaceflight to Mars
• Why We Can't "Backup Earth" On Mars, The Moon, Or Anywhere Else In Our Solar System
• Will We Meet ET Microbes On Mars? Why We Should Care Deeply About Them - Like Tigers
• No Simple Genetic Test To Separate Earth From Mars Life - Zubrin's Argument Examined
• Can You Suggest A Second Earth Apart From Mars?
• Does Earth Share Microbes With Mars Via Meteorites - Or Are They Interestingly Different For Life?"
  
• Could Microbes Transferred On Spacecraft Harm Mars Or Earth - Zubrin's Argument Revisited
• Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
• To Explore Mars With Likes Of Occulus Rift & Virtuix Omni - From Mars Capture Orbit, Phobos Or Deimos

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