First, to summarize, I don’t think we should send scientists to the Mars surface right now, because they will bring Earth microbes with them. It is very easy to find life if you bring it yourself, but that’s the last thing we want to do as it would obscure the search for past and present day life on Mars. But we can send humans to orbit and explore it telerobotically, or we can explore from Earth using robotic explorers as we do now. So how long would it take to do that? Well we might find life there right away with the first instrument we send to Mars able to detect life. We can’t rule that out yet, because we haven’t tried. There could be spores scattered through the Mars dust everywhere, hardy viable spores , or dead spores, just a few per kilogram of dust, and we just wouldn’t know yet. We could find that out with our first dedicated biological mission to Mars since Viking. Curiosity 2020 and ExoMars are more sensitive, especially ExoMars but they could still miss spores in the dust.

Or it may be really hard to find past or present day life there. So - a very rough estimate, maybe a decade, sending a dozen or so rovers and half a dozen orbiters every two years - to get a rough preliminary survey roughly similar to sending seven or eight rovers to each continent on Earth (the land area of Mars and Earth are similar). It would be more thorough if those rovers are very capable and able to travel hundreds of kilometers a day and with broadband communication back to Earth, all of which we could have in the 2020s potentially. But I’m basing that on hardly anything. As far as I know, nobody has tried to estimate this. It’s not even a “back of the envelope calculation”.

The robots can be either controlled from orbit, or very capable with autonomy, controlled from Earth. Controlled from orbit seems best but it’s hard to tell how much that would add to the cost. But scientists on the surface - well I don’t think we should do that at all, we should do the survey first, and then decide whether to send scientists to the surface after the first biological survey of Mars.

Many people assume, naturally enough, that we'd find life on Mars by searching for fossils. They search the rover images for fossils too. But we only had easy to spot fossils on Earth in the last 500 million years. Meanwhile places on Earth that are similar to the most habitable regions of present day Mars only have microbes and occasionally lichens.

So, Mars will only have easy to recognize fossils if it developed multicellular life at an early stage far faster than it developed on Earth. Mars could have the likes of microbial mats or stromatolites, but those are hard to distinguish from rock formations. So the search is likely to be done using ultra sensitive instruments able to detect the minutest traces of organics.

On Mars, unlike Earth, a single complex organic molecule could potentially be a major ground breaking discovery if you can prove it didn't come from Earth. And then we also have many potential habitats for present day life there too.

I should say for humans in space enthusiasts that this is not an argument against humans in space. I think humans can be of great value in space, on the Moon and in Mars orbit. See my Case for Moon First. I don’t think we should send humans to the Mars surface however, right now, and will explain why.

IN DETAIL

How long it would take would depend on how much we do. I think it’s hard to know if robotic exploration or human exploration would be faster. Humans in orbit around Mars could do it faster with fewer robots but at much greater expense. If you spent all the money you would on a human expedition on sending huge numbers of miniature rovers to Mars and setting up broadband communications, better autonomy, and artificial real time to control the rovers there from Earth, it might even cost less than a human expedition.

Hard to say which would do it faster. But probably human exploration mainly because we’d spend a lot more on it if we sent humans there because of the human interest. It’s all guesswork really as nobody has done a thorough comparison study. The main options are

• Robots on the surface controlled from Earth with much better autonomy, obstacle avoidance, more robust, faster moving (hundreds of kilometers a day), more power, and broadband communications back to Earth
• Humans in orbit around Mars controlling large numbers of robots on the surface (also controlled from Earth) with the humans in orbit stepping in to deal with the most tricky situations and experiments that need human interaction. I
• Humans on the surface.

If you kept the cost the same, then you’d have many more robots in the first case than in the second, and many more in the second than in the third, which makes it hard to compare them. Also humans on the surface have to put on their spacesuits to go anywhere, and that currently takes a whole day on the ISS to prepare for an EVA. And their gloves are clumsy, like wearing a hosepipe on your fingers, and rather painful to operate because of the pressure difference inside and out. And humans are not good at drilling in vacuum conditions of Mars, you can’t use water and we have self hammering moles that should be able to drill for hundreds of meters and then for kilometers on Mars.

However humans have the major drawback that they can’t be sterilized of microbes. They also have to live in spacecraft and habitats that are swarming with trillions of microbes - on their skin, in the air, in their food, the soil, everywhere.

For past life, we want to send instruments to Mars so sensitive they can detect a single amino acid in a one gram sample. We want to send DNA sequencers to search for DNA to see if it is DNA based. The ancient amino acids and any ancient RNA or DNA on Mars are going to be hard to find, because the surface radiation can destroy meters thickness of organics over billion year periods (it’s exponential so doesn’t have much effect on short timescales). Not only that, Mars also has a constant rain of organics from comets and meteorites. The organics Curiosity found so far they think come from meteorites, and the big surprise was that it didn’t find them sooner. There’s some process actively destroying it, probably the reactive surface chemistry. So you need to find organics that was buried deep enough to escape the surface radiation, so that means ideally ten meters, and at least 2 meters. It needs to have life in it, and not be mixed with the meteoritic organics, or any other organics produced by natural processes such a serpentization, asteroid impacts, volcanic processes and so on. It needs to have been unearthed rapidly (within a few million years and ideally faster). It also needs to have not been washed out by later flooding either. And then you are looking for degraded organics.

So we may well need all that sensitivity of our instruments to detect those organics and to solve the detective puzzle of whether it was originally life or not before the ionizing radiation and the natural radiation of the rocks over billions of years degraded it.

For present day life, we are searching for microbes that may be impossible to cultivate in vitrio (only 1% of Earth microbes can be cultivated, and on Mars we may be talking about a new form of life never encountered before). We can send microbial fuel cells that can detect just a few microbes - not even reproducing, just respiring. We can search for just a single amino acid in the sample once more, this time searching for present day life. We can use devices like Solid3 which uses polyclonal antibodies to detect life again in minute quantities.

So - can we do that with humans on the surface? It’s hard enough sterilizing a robot on Earth to send it to Mars and not risk contaminating it with Earth microbes. But what about a rover sent out from a habitat occupied by humans on Mars? Can they sterilize the rover, over and over, to such a level of sterilization that it can’t contaminate the samples even with a single amino acid? Or if the rover never comes back to base, what is the point in having humans on the surface? Why not have them in orbit? But the situation is worse than that, because the humans could crash - indeed, it’s one of the most risky missions we could attempt with humans in the near future.

Mars is most similar to our coldest driest deserts. But we have to think of these as analagous to the most habitable places on present day Mars. So if there is life there, it’s probably in tiny thin films of salty brine, or possibly fresh water trapped by ice. It’s likely to be very sparse - some places have it, others don’t, and just a few cells.

The very last thing we want is this -

Early artist’s impression of supersonic retropropulsion

followed by this:

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

followed by this

This shows photographs taken by Opportunity during a dust storm from sols 1205 to 1236 (one month). Each horizon view has been compressed horizontally (but not vertically). By the end of this period it reached a visual optical depth tau 4.7 which means that 99% of the sunlight was blocked.

And this

Global Mars dust storm from 2001 Mars has local storms every two years, and from time to time it has larger global storms. The first global storm recorded is from 1873: the other ones reported were in 1909, 1924, 1956, 1971, 1973, 1975, 1977 (2 storms), 1982, and more recently in 1994, 2001 and 2007. So we get a global dust storm roughly every decade or so, though sometimes several per decade (five storms in the 1970s)..

After that, there could be microbes from Earth just about anywhere on Mars. The Mars dust storms can protect the spores from UV radiation, if hidden in a crack in a dust grain.

To get an idea of how vulnerable Mars habitats could be to modern Earth originated life, one possibility for Mars is an early life form. Like the hypothesis of a shadow biosphere, on Earth - the idea that RNA based life, or some other form that predated modern DNA life might still survive here to this day. So far nobody has found early pre-DNA life on Earth, which means it probably was made extinct by modern life. But Mars could have that “shadow biosphere”, and it could be vulnerable to whatever made it extinct on Earth.

NASA and others have the idea that they can land humans within a few kilometers of a place of interest such as a warm seasonal flow, send automated rovers up to it to examine it and bring back samples for them to study in their base and keep the contamination contained around their base.

From this 2015 report:

• "No habitat or EVA system will be fully closed. Therefore missions carrying humans to Mars or other bodies will contaminate the planet."
• "The increased capabilities that human explorers can contribute to astrobiological exploration only exist if human associated contamination is controlled and understood. It is therefore critical that attempts be made to seek evidence of putative past and/or present extraterrestrial life, especially on Mars, well before these missions occur and to identify, characterize, minimize, and control contamination sources and pathways that would threaten such evidence."

So their aim is to land humans on Mars and search for life with the idea that they are going to contaminate the planet, but that they will find out as much as they can about the life there before they do so.

I don’t think is the right way to do it myself. And that is not taking account of the possibility of a crash on Mars. When asked about that they just say “that’s for the mission planners to look into”.

It’s different for robotic missions. You have to look into the planetary contamination effects of a crash on Mars as part of your plans. But for humans, then it would be impossible to send humans to Mars if they did that, not if you want to avoid contaminating it with Earth microbes, so they just assume that the human occupied spacecraft won’t crash.

But we don’t yet have final conclusions about how to land humans on Mars consistent with planetary protection.

I think we should explore from Earth or from orbit around Mars, and leave decisions about whether to send humans to the surface to a later date.

So how long could it take to do that exploration? Well Mars is vast, same land area as Earth. Imagine doing a biological exploration of Earth, with one rover in each continent, with three of them able to travel 100 meters a day, kilometers total, another one (Sojourner) able to travel meters, and the rest stationary. And of all those, only two have had instruments that would let them detect life. And now you are exploring a planet that is entirely desert, no trees, no plants, no open water or streams or rivers. Yet with a varied landscape as varied as on Earth. And now, add to that, that there are only a few patches here and there that could have present day life, that most scientists think life is impossible everywhere else, (though some think it might just about be possible). That those habitats are, most of them, hidden in cracks or below the surface of rocks or a few cms below the surface of the soil or ice. And that though we have found some habitats that we think could have life in them, just possibly, we haven’t visited any of those yet. And add to it that we must not introduce Earth microbes to any of those habitats if we want to find the native life. And that there’s that constant rain of organics from comets and meteorites and the other issues with finding present day life.

As for past life, then we don’t know if it ever evolved. If it did, we don’t know if it evolved photosynthesis. It could be very localized, but if so, we don’t know where to look for it. Ancient hydrothermal vents perhaps? Ancient lake beds (but those become much less plausible if it didn’t evolve as far as photosynthesis). And then we have to find life that was buried rapidly and then unearthed rapidly first.

It could still be there today, but we have dozens of places we can look for it again.

It’s not easy. You wouldn’t expect to know much about it yet.

So - it’s hard to say. Some think Viking found life already, especially after the discovery of what seem to be circadian rhythms in the labeled release experiment data. If that is right, then the first mission to Mars that is able to duplicate the Viking experiment may find life there right away. There may be spores in the dust wherever our spacecraft have traveled on Mars - and we simply wouldn’t know yet. Because we haven’t sent any experiments since Viking sensitive enough to spot just a few spores in the dust.

Patterns characteristic of circadian rhythms in the Viking labeled release data. The interesting thing is that they are significantly offset from the temperature variations, which to an expert on circadian rhythms who spotted this, strongly suggested life rather than non life processes. More on this in the section Rhythms from Martian sands - what if Viking detected life? in my book, and following

If that’s right, we may find life there rapidly. Maybe ExoMars will find it, as it is much more sensitive to organics, though it doesn’t have the ability to put it in a nutrient like Viking and see if it respires.

But it might take a lot longer. I tried to get an idea of what is needed for a reasonably thorough first survey of the most interesting places on Mars, in my section: How many years are needed to do a biological survey of Mars?

For present day life we need to look at:

• The Recursive Slope Lineae (RSL's). You would need to send missions to more than one of those as they are especially interesting, geographically isolated and it's possible some have life and some don't.
• The flow-like features in Richardson's crater near the south pole. This may consist of fresh water trapped under ice, so are especially interesting for viability
• Clear ice in the polar regions generally - is there liquid water trapped beneath it?
• Dust grains in the snow or liquid water around meteorites caught in the polar ice?
• Check the polar ice caps for deep subsurface water, using radar, and if any is found, to drill down to search for life (if liquid water forms at depths of over 900 meters after a meteorite impact or through geothermal heating, it will remain liquid indefinitely through the flow of heat from Mars itself insulated by the ice above - See page 191 of this paper. We can say that Mars doesn't seem to have an equivalent of our Lake Vostok (250 km by 50 km by 0.43 km deep) at present. It could still have small subglacial lakes of up to a kilometer or so in diameter.
• Equatorial sand dunes. Levin thinks Viking discovered life already, and recently with discovery of circadian rhythms in the re analysed experimental data, others think there is a possibility of that also. Then, whether Viking found life or not, there are ways they could be habitable. So we need to check up on that to be sure. Also Curiosity found a liquid water layer a few cm below the surface of the sand dunes indirectly. Nilton Renno has suggested that microbes could find a way to create a niche in it, by transforming the environment as it can do on Earth even though the data suggests it is always either too salty or too cold for life. [ExoMars may give the first ideas about this - though it's not quite as sensitive as Viking's labeled release, it could find life in the Atacama desert core which Curiosity couldn't]
• Salt / ice interfaces. Nilton Renno's "swimming pools for microbes" in droplets of water that form where salt touches ice. We'd need to search in places with different salt compositions as that would affect the habitability.
• Salt pillars and salt deposits, for deliquescing salts, and for water that can form in fine pores in salt pillars.
• Caves need a visit. Not so much lava tube caves as other types of caves, for instance ones formed by slippage, or ones that formed through erosion by water or dry ice. The difficulty is, they are hard to spot form orbit. We do need survey not just orbital images, which are also limited to particular times of day and such like. E.g. miniature planes to fly along the Valles Marineres to photograph it up close.
• We should explore the surface itself for life, for lichens and cyanobacteria that might be able to grow in partial shade, using just the night time humidity, according to the DLR experiments.
• The Hellas basin because of the icy mists that form there and because it is the densest atmosphere on Mars which could make a difference to habitability.
• Study the Martian dust as it might have spores in it from anywhere on Mars.).

And if you drill deep enough you reach the hydrosphere, a theorized layer deep down where the rock gets hot enough to keep water liquid, and it’s trapped by the layers of rock above it. We find life on Earth in deep mines, so if there ever was life on Mars and it evolved far enough to colonize its hydrosphere, it’s probably still there as nothing has happened to Mars that could have made life in its hydrosphere extinct.

For past life we need to look at

• Salt lake deposits
• Clay deposits
• Fossil hydrothermal vents
• The depths of craters which may have exposed deep subsurface materials.
• Ocean beds
• Deltas
• Fresh water lake deposits
• Rivers
• Caves - not just lava tube caves but caves formed from water erosion, dry ice, geological faults, asteroid impacts
• Regions where the ice was melted in the past from asteroid impacts
• Volcanic regions

Also just one of those sites may be as intricate as this

Chemical Alteration by Water, Mawrth Vallis (Mawrth Vallis is the second of the two landing sites selected for ExoMars. The first one is Oxia Planum).

And then you have to drill to depths of meters to find deposits that don’t have the ancient organics completely destroyed by ionizing radiation.

So - we might strike it lucky and find life early on. If Mars life evolved as far as photosynthesis and developed the robust spores of present day Earth life, perhaps it is in nearly all those habitats, both past and present, and if so, maybe we find it quite quickly. But if it didn’t evolve photosynthesis - well photosynthetic life doesn’t get transferred between planets as easily as some other forms of life - so maybe it hasn’t yet got photosynthesis to this day. If so, then life might be rare and hard to find.

The last chance for life to get from Earth to Mars was the Chicxulub impact 66 million years ago. The jury is out on whether it did or not. It has to withstand the shock of ejection from Earth, burning of the crust as it leaves Earth’s atmosphere, the vacuum of space for a century, but probably more, solar storms, impact on Mars and then find a habitat there. This is especially hard for photosynthetic life, both less impact resistant, and it also tends to be near the surface of the rock so would be burnt off.

It might not have happened for billions of years. The best time was soon after the formation of the Moon during the Late Heavy Bombardment - but was early life back then robust enough to withstand the passage to Mars or vice versa? At the present all options are open - closely related life, distantly related life, and life that’s a second genesis. Astrobiologists designing instruments for Mars do not assume that any life there is going to be DNA based. We might well send DNA sequencers there to try to sequence it - but it would be even more interesting if those sequencers don’t find any DNA.

Carl Sagan estimated 54 rovers on the surface and 30 orbiters as his idea of what was needed for a biological survey of Mars. It was just figures he plucked from the air for a calculation. But nobody has come up with any better figure since then. He wrote that in the mid 1960s. His idea of a biological experiment on Mars was crude by modern standards of course. But he also assumed a much more hospitable Mars than we now understand it to be.

Perhaps it’s not a bad estimate even now for a first attempt at a biological survey of Mars. If you compare it with Earth’s continents, it’s like sending 7 - 8 rovers to each continent. If you think in terms of the Mars habitats, it’s enough to send a couple of rovers to each type of habitat of interest, past or present. If we can make the rovers mobile and semi-autonomous able to travel hundreds of kilometers a day, it would make a huge difference. If we have broadband communication back from Mars to Earth it would also make a huge difference. I don’t think many people have really taken that into account yet as we have no experience yet of exploring even the Moon with broadband communications - even the Apollo missions weren’t quite like that.

When we get a broadband connection to Mars in the 2020s, this will change things dramatically. With a bandwidth of hundreds of gigabytes a day, we will be able to download 3D landscapes from Mars dozens of times a day. These will be so detailed that anyone on Earth can study rocks close to the rover, not just in 3D, but with the ability to zoom right in to observe them in microscopic detail.

We have never had that capability before and I think it’s hard to know what a difference it will make. Same also for the ideas of microrovers. When we can send dozens, even hundreds of micro rovers in a single mission to Mars, what difference will that make? Even without humans in orbit to direct them?

Now, I don’t think that 54 microrovers in a single mission will let us do a complete biological survey of Mars, even a first try at one. We have to send them to all those different habitats, they have to be capable of drilling at least 2 meters and better, 10 meters for the search for past life and we need multiple detection methods for present day life to back each other up. 54 highly capable rovers dedicated to a biological survey maybe? We also can’t do it all in one mission because later ones will build up on earlier ones.

My conclusion to that section was:

“I wouldn't like to estimate how long such a vigorous program of exploration would take. But on the face of it, it seems more like years than decades. At a dozen rovers and half a dozen orbiters sent every two years, it would take about decade, based on that number of fifty four landers which we rather "plucked from the air" for illustrative purposes”

It needs a proper study but nobody has done one as far as I know. Nor do we have any attempts at a comparison study of robots controlled from Earth with telerobots and humans in terms of cost effectiveness - except the HERRO one - which was done by researchers keen on telerobotics, but with old data now, as telerobotics has moved on since then.

Anyway to find out more see my online and kindle book

OK to Touch Mars? Europa? Enceladus? Or a Tale of Missteps?

(It is still work in progress. I got caught up with other things but plan to return to it to finish it soon).

See also my wikipedia articles:

Modern Mars habitability - Wikipedia

Present day Mars habitability analogue environments on Earth - Wikipedia