If we send humans to Mars then we'll almost certainly introduce Earth life, if there are any habitats there suitable for Earth life. And we wouldn't necessarily be able to tell if it was from Earth or from Mars.
WOULD LIFE ON MARS BE RELATED TO EARTH
Robert Zubrin has said he thinks there is life on Mars and that it is related to Earth life. But that's just a view of one person, and not an astrobiologist either for that matter.
As so often in science, are many ideas about this.
Yes, it is now thought to be theoretically possible for Earth life to be transferred to Mars via meteorites and vice versa, this is just a theory, and has not been proved. We don't yet have a single example of a lifeform that got transferred between planets on a meteorite.
If this is possible, it was easiest in the early solar system when there was lots of debris exchanged between the planets.
The debris spends a minimum of a century in the harsh environment of space, and it then would land on a planet that though it may have habitats for life, is not the sea covered early Mars and harder for introduced life to gain a foothold.
We just don't know if Mars life will be related to Earth life or unrelated or a mixture of both.
TELLING LIFE APART IF IT IS BASED ON A DIFFERENT BIOCHEMISTRY
it's likely (not certain though) to be easy to tell - if it has no common ancestor - the chance it is the same is minute, probably. Could be mirror image life. Could have a different backbone, PNA, TNA, RNA only etc - and there are thousands of different molecules that could be use as alternate bases and on the face of it unlikely that alternatively evolved life uses exactly the same bases as DNA based life. Which would mean it can't even be DNA sequenced unless you know what bases it uses.
Some biologists have tried to argue that our DNA based life is so unique, so much better than any other option - that independently evolved life would have to follow the same pattern, there are many other options but would they be as good as DNA based life?
But I think many would say independently evolved life is likely to be different enough to be easy to distinguish.
TELLING IT APART IF IT HAS A COMMON ANCESTOR
But if it does have a common ancestor, that's when it gets really tricky. It could have a common ancestor at any point in evolutionary history, e.g. from before DNA (DNA is unlikely to have existed in the first lifeforms to evolve) perhaps RNA life only. Or from a few billion years ago, before development of the nucleus, or more modern life. The most likely time for the planets to share lifeforms is in the early solar system over three billion, maybe over four billion years ago.
And - the thing that complicates it most of all as I say in my answer is that first, most microbes are not DNA sequenced and entire phyla of archaea, because they can't be cultivated currently, are known only from a few fragments of DNA - that's just a few fragments representing an entire phylum with numerous species in it.
Also if it had a common origin even billions of years ago, then that means that gene transfer is possible. So after contamination with Earth life you end up with a mix of Earth and Mars DNA- some of the lifeforms would ber original Mars life, some Earth life, some Earth life that's taken up sequences from Mars life, and some Mars life that's taken up DNA sequences from Earth life. And that exchange can happen even with GTAs from dead microbes of either type.
So it's more tricky than you might think on first encounter with the question.
WOULD MARS LIFE SURVIVE AN ENCOUNTER WITH EARTH LIFE - OR VISE VERSA?
If Mars life has a radically different biochemistry, e.g. based on PNA or an early form of life with only RNA and no DNA, say, then yes, we'd be able to tell - that is if it survived the encounter with Earth life. It might not.
Some try to argue that Mars life would be better adapted than Earth life so would be sure to survive - but that's not true. For an example, rabbits are better adapted to Australia than many native marsupials.
SIMPLE EXAMPLE, EARLIER FORM OF LIFE ON MARS
An easy example there - it's quite possible that Mars only has early forms of life. Modern DNA based life just couldn't have evolved in a single jump from a chemical soup, with all its complex machinery. Particularly the Ribosome (which turns messenger RNA into proteins) and the complex DNA to RNA transcription machinery must have had simpler precursors. Also, the smallest size of cell all this could all fit into is about 200 nanometers across, coincidentally the size of the ultramicrobacteria the smallest lifeforms known, and coincidentally, also the diffraction limit for optical microscopy.
See Constraints on Size of a "Minimal Free-living Cell"
There is no way a functioning 200 nanometer diameter cell could spontaneously form from just a mix of non living chemicals, complete with Ribosome, gene transcription, DNA, messenger RNA, proteins, etc.
So must have been precursors. Perhaps about 40 nm across is one estimate, from that same workshop. And before that, non living but "almost alive" intermediaries, with one suggestion, an "RNA ocean" and another, autopoetic cells, where there is a kind of a metabolism inside a cell structure, but no exact replication yet, just approximate replication as the cell grows and then splits, or creates a daughter cell inside which escapes.
Mars has had less time for life to evolve than Earth, with its early sea drying up after a few hundred million years. That could mean that any lifeforms there are at an earlier stage in evolution. On the other hand it has had many episodes of freezing and melting, possibly with its much more elliptical orbit then at times the entire ocean froze over and melted again every two years - and much higher levels of cosmic radiation, and is different from Earth in many other ways - any of these could either accelerate evolution or slow it down. And life if evolved a second time on an Earth like world could either evolve more quickly or more slowly just by chance.
So there is no way of knowing if life on Mars is evolutionarily ahead or behind Earth life, or possibly followed a different direction.
If it is an early fragile form of life, the Earth life could just 'eat it up".
In this case it would be easy to tell it apart from Earth life, but by the time we are able to do a thorough investigation, there might not be any Mars life left.
CONTEST OF MORE ADVANCED LIFEFORMS - E.G. IF MARS OR EARTH LIFE IS BETTER AT PHOTOSYNTHESIS
Also, for more advanced life, there is no way of knowing in a contest between Earth and Mars life for the same habitat, which would win. For instance what if both planets have independently evolved photosynthetic lifeforms? That's well possible since Earth has at least three distinct main forms of photosynthesis, and one of them - the haloarchaea which use rhodopsin to convert light directly to energy without generating any byproducts such as oxygen or sulfur dioxide. The other one works by oxidising hydrogen sulfide or other reduced sulfur source. Anoxygenic photosynthesis
So what if Mars life has a fourth or fifth form of photosynthesis? It might be more efficient than Earth life, or it might be less so. Also Mars life might have a more or less efficient metabolism generally.
EFFECT OF MARS LIFE ON EARTH LIFE
This is mainly about the effect on Mars life - but since many say that Mars life couldn't possibly harm Earth life either - in the other direction, Mars life could also be harmful to Earth life too.
If related to Earth life - well legionnaires disease originated as a disease of amoeba - so it doesn't have to be a disease of humans or even animals to be harmful to us. Or to animals we depend on, or plants, or anything in our biosphere.
And if unrelated - it doesn't have to be biologically compatible to be harmful. Our bodies defend themselves by recognizing carbohydrates and peptides in the invading organisms. If they don't produce these chemicals because of some radically different biochemistry, our bodies won't know to defend against them. They could just grow in our lungs, sinuses, intestines etc, do whatever they do normally on Mars in these new environments, and our body would do nothing to stop them. And extremophiles often can also reproduce just fine in less harsh environments.
It's impossible to estimate a probability here. Most would say it is very low. But then on the other hand when scientists make new forms of artificial life in the laboratory, e.g. a recent experiment that proved inheritability of DNA with two extra bases added - they are very careful to make sure this new form of life can't reproduce in the wild. Because we don't know what would happen if some new microbes with 6 DNA bases instead of 4 were to start to spread in the wild. Most would assume that they would be harmuless and that the life with 4 bases would out compete them. But we don't want to do that experiment. It's the same with Mars life.
Or what if it is the Mars life that is more advanced biochemically than Earth life? More efficient metabolism say? We don't know what controls the speed of evolution and it might be that something about Mars conditions such as the extra radiation there, or the alternating wet then freezing conditions in early Mars accelerated the pace of evolution.
However for this question, we are more interested in whether the Earth life would make the Mars life extinct.
EARTH LIFE MAKING MARS LIFE EXTINCT
In a situation like the one with an earlier form of life on Mars, the Earth life could make Mars life extinct before we can study it thoroughly. Mars has a connected atmosphere, with global dust storms, and after a human landing, especially a crash landing, then the very hardy Earth spores, able to survive for millions of years on Earth will spread in the Mars dust, imbedded in dust grains so protected from UV light.
No matter where the crash happens, after a human hard landing, it seems likely that eventually some of those spores would reach the special regions where, on present understanding, Earth life compatible habitats are possible.
WHY WE CAN'T TELL WHETHER THE LIFE CAME FROM EARTH ON OUR PROBES VIA GENE SEQUENCING
Then - if Mars life is related to Earth life, then again it would be impossible for us to know if it came from human contamination or from Earth via meteorites. Most of Earth life is not sequenced, and entire phyla of archaea are only known by a few gene fragments. We'd recognize a gene sequence of a known Earth microbe, say Chroococcidiopsis , one of many Earth lifeforms likely to be able to survive on Mars. But we couldn't recognize microbial dark matter on Mars as of Earth origin by its gene sequence.
In any sample of microbes from an Earth environment, typically 99% of the microbial population have never been uncultivated in a laboratory, and even fewer are sequenced.
This is true even of the spacecraft assembly clean rooms, never mind human occupied spacecraft. Most of the microbes in those rooms, after they clean the spacecraft, are unknown to science. All we have are a few DNA fragments. That's not surprising as it is true of just about all habitats where you find life.
Current planetary protection is a matter of probabilities. Since we can't sterilize spacecraft 100% quite yet, we sterilize them as best we can to a point where we think there are so few microbes left that the probability they will contaminate Mars is minute. Carl Sagan's original target was a 1 in a thousand chance of contaminating Mars during the period of biological exploration - which we have barely started, haven't yet sent a single spacecraft to Mars since Viking capable of detecting past or present life because all the successful missions since then have focused mainly on habitability, including water and organics, not life detection. ExoMars in 2018 will be the first mission since Viking to have a possibility of unambiguous life detection on Mars - except of course for very obvious things like macro fossils.
UNKNOWN MICROBES TO BE EXPECTED ON A CONTAMINATED MARS
So if we found an unknown microbe from Mars, that would be expected, if it was contaminated by Earth life, as we find unknown microbes all the time in Earth habitats. Most of the microbes in any human occupied spacecraft would be unknown and unsequenced, especially the archaea. Basically unless it is in some way hazardous to humans, or beneficial to us, the chances are high that we have no idea of its gene sequence.
WHAT IF WE DO FIND RELATED LIFE - HOW CAN WE KNOW IT GOT THERE ON A HUMAN SPACECRAFT?
And then - what if we did spot a gene sequence for Chroococcidiopsis, say, on Mars? How do we know that it got there on a human spacecraft? It could have got there on a meteorite.
Last chance of that happening probably tens of millions of years ago as it needs a giant impact on Earth to send microbes to Mars. Most likely to happen in the early solar system billions of years ago. But that's an ancient stable lifeform on Earth.
And here also it has many subspecies, slight changes in its genes.
So if we find it on Mars, it might be similar, might be different, might be evolved in another direction.
ALMOST IDENTICAL LIFE OF GREAT INTEREST
If it is almost exactly the same, that would be a matter of great interest.
So - this doesn't mean it doesn't matter if you introduce the Earth variety of a microbe similar to one that is already on Mars.
We'd want to disentangle the two and find out if there are differences in the Mars variety and why, and how it has varied, and try to figure out when it last split off from the Earth variety. That would be much harder to do if the Mars populations become a mixture of individuals some from Earth and some native to Mars.
FINAL COMPLICATION - GENE TRANSFER AGENTS AND ORGANISMS SHARING GENES FROM BOTH MARS AND EARTH
And then a final complication. If Mars and Earth life is related, but perhaps split off from Earth life in the early solar system, three billion years ago or more - it may be closely enough related to share genes with Earth life. The mechanism of Gene transfer agents is an ancient one, and Earth microbes in totally unrelated phyla share DNA fragments readily and rapidly.
Even higher lifeforms do, including for instance an aphid which shares the genes for generation of carotene with a fungus, so at some point the gene fragment that creates carotene (the chemical that makes carrots red) got transferred from a fungus to the aphid - which it uses to turn its body red.
So after introducing Earth life to Mars, if the life is even remotely related, then you would end up not just with the Earth and Mars versions of the lifeforms - abut also with mixtures, in both directions, of gene sequences of the Earth and Mars microbes, especially of the archaea.
From time to time, you'd get higher lifeforms also incorporating Mars gene fragments as for the pea aphids. And the same also in the other direction if there are any Mars higher lifeforms at all - not totally ruled out, tiny multicellular plants, or even animal life as there are tiny Earth multicellular animals that are able to live their entire life cycle without access to oxygen (recent discovery a few years ago). They also could end up incorporating fragments of Earth DNA in them.
SENSITIVE SEARCHES FOR LIFE ON MARS ABLE TO DETECT A SINGLE AMINO ACID
And as well as that - our early searches for life would involve very sensitive searches for amino acids and other biosignatures. Some of these proposed instruments are so sensitive, they can detect a single molecule in a sample.
If you introduce Earth life, then searches for biosignatures are useless as they would only tell you that there is some form of life there, not whether it is Mars or Earth life.
SUMMARY - IN SHORT HUMANS CRASH LANDING ON MARS SERIOUSLY COMPROMISE THE SCIENCE WE CAN DO THERE
In short, if humans crash land on Mars, then that would seriously compromise the search for present day life on Mars. It would also cause problems for searches for past life too.
HUMANS IN MARS ORBIT OR ON PHOBOS OR DEIMOS - SAFEST APPROACH WITH BALLISTIC TRANSFER OR FLYBY
If we want to send humans to Mars, I think we should send them to Mars orbit or to the Mars moons of Phobos or Deimos - and do it in such a way as to make sure there is no chance of a hard landing. That is possible using a method called "ballistic transfer" where the spacecraft ends up in a distant orbit around Mars and then slowly spirals down perhaps using ion thrusters. There is no insertion burn needed at all.
The insertion burn is the riskiest part of any Mars capture scenario - because you need a precise length of burn to get into Mars capture orbit, and usually done close to Mars as it is more efficient deep in its gravity well. If it lasts just a bit too long, you could crash into Mars far from your intended location. So I think human missions to Mars should avoid insertion burns, both for safety of the crew, and for planetary protection reasons.
The ballistic transfer orbit is promising here, and NASA do plan to explore it in future Mars missions. It doesn't save much by way of fuel - is much less fuel to get into the distant orbit - but you then have to spiral down, and if you want to get as close, say, as the Mars moons, then there isn't much in it by way of fuel saving. But you can use the more efficient ion thrusters, and it is much safer.
Another good approach is to do a flyby of Mars. Because again there is no insertion burn. And you have all of the approach to Mars to do fine adjustment of trajectory - and can use trajectory biasing where the spacecraft is not directly aimed to hit Mars at launch, but to one side, then slowly nudge it into the right orbit. This is very safe - our spacecraft like Cassini are able to do extremely precise flybys using this approach.
ROBERT ZUBRIN'S DOUBLE ATHENA
One especially interesting idea here is Robert Zubrin's "Double Athena" which does one flyby of Mars to get into an orbit that almost parallels Mars, then after a year of study, another flyby takes you back to Earth. And it's a "free return" trajectory - once committed to it, you will come back to the vicinity of Earth even if you never make any more engine burns. So it's also very safe for human astronauts.
If we can sort out the many challenges to send humans away from Earth without resupply for the 700 days of the double Athena safely, I think it is a natural first human mission to Mars. And you'd do study of Mars via telepresence when close to the planet. Then you could use sun precessing Molniya type orbits for longer term study of Mars, and then after studying its moons remotely first to know more about them than we do now, could land humans there first.
BEFORE LANDING ON MARS MOONS - WHAT IMPACT DOES A HUMAN SETTLEMENT HAVE BY WAY OF TRASH AND HUMAN WASTES?
Though especially as they are tiny moons, need to have an idea of how much impact humans have on a place if they set up base there. By then we probably know about that from the Moon - do they inevitably surround their base with tons of trash and human wastes? If so maybe we should avoid sending human missions to those tiny moons quite yet.
WHY I CAN'T SEE COSPAR APPROVING A HUMAN LANDING ON MARS
I'm pretty sure that a human mission to the Mars surface would get surrounded by trash and human wastes if done with present day technology - even burying it wouldn't help. It would be too much to expect for them to keep all their trash and human wastes inside the habitats, and recycle the air without ever venting it if it goes bad.
And anyway the air would be vented every time they go out of the spaceship. We are nowhere near the level of technology needed to land a biohazard laboratory on Mars with the microbes in the human habitat as the hazard to be contained and kept away from Mars and the Mars duststorms.
But you don't need to think about that, since most are agreed there is a reasonably high chance of a crash landing in the early stages of an attempt ot send humans to Mars, and that is an immediate planetary protection fail.
For this reason, I can't see COSPAR approving a human mission to the Mars surface unless we first decide there is no longer any interest in the search for independently evolved life on Mars, or decide that present day habitats for life on Mars are impossible.
Some scientists seem optimistic that somehow a human mission to the Mars surface can be done consistent with planetary protection. But many others have said this is impossible. COSPAR workshops on this topic generally end with the conclusion that further research is needed.
I can't see how they can approve a human mission to the surface without relaxing planetary protection requirements, and don't see how there can be any scientific justification on present knowledge for doing that. If there was a human mission to Mars surface, then at some point a team of experts, exobiologists and so on, would need to decide that it is safe under the Outer Space Treaty and not in conflict with the science interests such as the search for life on Mars. I just can't see that happening any time soon.
HUMAN MISSION TO MARS ORBIT LIKE ISS ABOVE EARTH - ICE CAPS, CLOUDS ETC
And a human mission to Mars orbit or a flyby or perhaps to its Moons would be a very exciting mission thath would also engage the public. And better psychologically I think also, able to look out of their windows at another planet, not Earth, similar perspective to the ISS looking down on Earth but looking down on Mars, its ice caps, dust storms, thin wispy clouds that come and go, volcanoes etc.
EXPERIENCE SURFACE VIA TELEPRESENCE - EVEN BLUE SKY ON MARS IF YOU LIKE
Then using the likes of the Occulus Rift, perhaps even something like the Virtuix Omni to "walk" around on the surface, you could explore via telepresence with binocular vision and haptic feedback, for that matter you could also use binaural recording to hear sounds in 3D too - and all that with enhanced vision, sound, etc, e.g. digitally enhanced so the surface looks as if illuminated by bright Earth sunlight.
Even a blue sky if you prefer it that way :). That's just a matter of white balance, if exploring via telepresence, to make the Mars sky blue instead of a dingy muddy gray brown which I think would have psychological impact long term.
We are making lots of progress with telepresence. And remember that astronauts would use the very clumsy pressurized spacesuits, with hands especially so stiff that it's described like having your fingers in a garden hose. They are exhausting to wear and simple movements get tricky as you see for the ISS space walks. Also via telepresence you'd be able to control rovers anywhere over the surface of Mars whenever your spacecraft is overhead. Which you can arrange to happen, for instance, twice a day on opposite sides of Mars each time when the surface is fully illuminated, and with several hours of close up time each time - that's the HERRO sun precessing Molniya orbit scenario.
WHY THE SEARCH FOR LIFE MATTERS
Because of what we could learn for biology. We have only one example of life and it is amazingly intricate and complex. Just one other example would like adding an extra dimension to biology - also to nanotechnology. See also Will We Meet ET Microbes On Mars? Why We Should Care Deeply About Them - Like Tigers
About the Author
