Why we shouldn’t send humans to Mars

Mars surface. Image courtesy of NASA.

The question isn’t really “Can we technically send Humans to Mars?” because sooner or later we’ll be able to — most likely thanks to Elon Musk’s hard work.

The real question is: “Is it desirable? Shall we go?”

And I believe that the answer is: no, we should not! There are two main reasons for this:

  • It would increase dramatically the risk of forward contamination of the Mars surface with our earthly microbes, which would ruin our unique chance to study a pristine Mars.
  • All the reasons advanced to vindicate the act of Humans traveling to Mars are either wrong or can be addressed in a way that spares Mars.

Here is the rationale:

We cannot rule out the existence of habitats where life can metabolize on an uncolonized, untouched Mars surface. And I do mean surface: many ideas of such surface habitats have been suggested (salty seeps, melt water under clear polar ice, ice fumaroles, dune bioreactors, among others).

If Humans go to Mars, they’ll have no choice but to bring with them their microbes — this is inevitable. For a start, there are more microbes in our body than even body cells — and we’re not even counting microbes in the air we’ll breathe in the ship and on the Mars base. These microbes are bound to find their way to the Mars surface at some point, whether it be after a crash (close to two-thirds of the 40+ missions to Mars have failed to this day), or because of air leaks from the habitat’s airlock, or from the spacesuits which are designed to leak some air at the joints to facilitate movement.

Some of our microbes will be able to resist for quite some time the harsh Martian environment — at least as spores. We call them ‘extremophiles’; Chroococcidiopsis, for instance, is a microbe that can withstand huge temperature swings as well as prolonged ionizing radiations.

Mars is a connected environment as it has an atmosphere—albeit a thin one—and has large dust storms that sweep across the whole planet. No matter where Earth microbes would be released, they would reach potential habitats in a matter of years, or decades at most. The iron oxide found in the dust would actually protect microbes from UV radiation. And while cosmic rays can penetrate meters of regolith, their level on Mars is similar to those in the ISS. Therefore, radioresistant terran extremophiles (there are many) could definitely survive them for thousand of years in complete dormancy — just as they would survive the occasional solar storms until they reach the safety of a possible Mars surface habitat where they can wake up.

Once in these habitats, if they exist, they could start again to metabolize and grow. It has been demonstrated that some cyanobacteria, when put in a chamber simulating Mars surface conditions (same air, temperature, pressure, UV, etc.) and partially in the shade, are able to show measurable activity and carry out photosynthesis, absorbing humidity from the atmosphere (relative humidity reaches 100% at night on Mars). Lichens, which are multi-cellular lifeforms, did the trick as well!

Our microbes could possibly then share genes with some potential Mars life (if they share a common ancestor), which would completely confuse our search. Their amino acids would get mixed up with current Mars life (if any), remains of past Mars life (if life ever arose there) or any pre-biotic chemistry on its way to life. That would again confuse our devices and ruin the whole study.

We cannot rule out a common ancestor for Earth life and possible present or past Mars life. Life could have originated on Earth and contaminated Mars through panspermia, or the other way around (as Mars had a liquid ocean before Earth did), or maybe life came from elsewhere and contaminated both planets. In such a scenario, any Mars life would probably be our Archaebacteria’s cousin.

We have so far identified—let alone DNA-sequenced—a very limited share of the Earth’s microbial world. Some microbiologists say there are probably thousands of billions of microbe species on Earth, 99.999% of which have not been identified! Only 10 million species have been documented, out of at least one thousand billions, out of which 100,000 have been DNA-sequenced, which is 0.00001% of the total! And even fewer, 10,000, have been grown in Petri dishes. So in case of a mix up with Earth and any potential Mars life, how are we supposed to tell one from another? Why again take such a huge risk to confuse the study? 

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Lastly, we cannot rule out either that our microbes will threaten potential Mars life, or its remains, whether directly or by accident. See the Legionnaires’ disease, caused by a microbe that evolved to feed on the Ameoba, but which happens to be able to target our white blood cells by pure coincidence and thus infect humans. Or Earth life could simply end up eating Mars life’s food and starve it. Any such harm would make the study of Mars (which had liquid oceans for a billion years) much harder, if not impossible. Mars would never be the same again—the irreversible move needs to be extensively debated before it is too late.

Potential Objections

There are 2 classical objections raised by Humans-to-Mars enthusiasts:

  • We have already sent our microbes to Mars with our rovers, so harm has already been done and it’s too late anyway.
  • Mars gets a lot of meteorites from Earth, and it’s possible that microbes could survive such a trip aboard a meteorite, so again any harm that could be done with Earth life has been done, so no need to fuss about that threat any more

These appealing objections do not stand up to close scrutiny. Here are some detailed rebuttals: Have we contaminated Mars already? and Does Earth Share Microbes With Mars Via Meteorites – Or Are They Interestingly Different For Life?

Others recognize these risks, but then argue that they are worth taking in light of what stands to be gained from sending humans to Mars.

Five mains reasons are put forward, with my rebuttals underneath:

  1. It will speed up our search for Mars life as humans will be more efficient than mere robots. This will more than compensate for the microbes we’ll bring with us. Rebuttal: That’s highly dubious, as robots actually let us do more using less money. Small robots can reach nooks and crannies that clumsy humans in spacesuits will never be able to. Robots will only get better and more autonomous thanks to AI. And we could also think of having people in the orbit of Mars remotely operating robots in real time on the surface — this NASA study says such a mission with six crew members in Mars orbit could achieve the same exploratory and scientific return as three conventional crewed missions to the Mars surface.
  2. It will be an engineering challenge that will capture the world’s imagination and generate a new wave of scientists, engineers and inventions we’ll all benefit from.
    Rebuttal: Not convincing, as there are so many other technical challenges we could, and have, set ourselves to overcome, like putting an end to climate change, or to hunger. Or what about building a base on the Moon, or a space orbital colony?
  3. To start a new civilization shaped by pragmatism and ingenuity, which will reinvigorate our current terran one.
    Rebuttal: One may argue that given the harsh realities of the Mars environment, communities and colonies there will be closer to the military style found in submarines than to what we think of as a libertarian utopia. In any case, such a goal would well be achieved at substantially lower costs here on Earth, and on our oceans to be more accurate, thanks to seasteaders!
  4. To ensure our species’ survival. We are supposedly threatened by life extinction events, man-made or otherwise, and we need to become a multi-planetary species as soon as possible. This is Elon Musk’s and Stephen Hawking’s thesis.
    Rebuttal: On close inspection, either these rare events would also annihilate any Mars settlement at the same time as Earth life, or they wouldn’t be life extinction events to start with. Meaning once event is over, there would be survivors, the Earth would remain the most habitable zone in the solar system for humans, and people the best positioned to repopulate it would be these survivors, and not far away Mars colonists. To read more detailed rebuttals, check out these articles: Why Resilient Humans Would Survive Giant Asteroid Impact – Even With Over 90% Of Species Extinct and Could Anything Make Humans Extinct In The Near Future?
  5. Because it would be fun, the most exciting adventure to watch, ever. Remember how the Moon landing got watched by 600 million people? That’s Elon Musk’s other reason to go: “it’s important to have a future that is inspiring and appealing. I just think there has to be reasons that you get up in the morning and you want to live” as he puts it.
    That would probably be the worst reason to jeopardize our unique chance to study a pristine Mars. And for the record, by the last moon landings, much of the public interest in them had petered out. Those who want to see humans land on Mars — so as to witness history — are probably the ones who will get bored the quickest after some time. Would it not be a pity to make such an irreversible move just for that one-time adrenaline rush?

But no harm building a Moon base! The Moon is actually much more interesting than most people assume. Learn about its advantages here.



  1. Excellent article and worthy of discussion and serious thought. I suspect that AI and robotic development will reach the point that by the time we can send and return a few people to Mars, we can send indestructible “human-like” robots that can accomplish the same things (and more) on a Mars mission that a real human could do, but without the life-sustaining needs and fragility of humans. It will cost far less and provide just as much information about Mars by sending artificial humans than the real things. It is great that we sent people safely to and from the moon, but now people have more computing power in their hands than the entire NASA space program in the moon flight years, so just imagine what IA and robotics will be like in 15-20 years. We need to put more effort and resources into satellites, ocean studies, climate studies, renewable energy, health, agriculture, etc. Science will improve life on earth just fine without sending humans to Mars. Sure Columbus succeeded in crossing the Atlantic ocean in primitive boats, but I’m sure he and his crew would have preferred modern jet travel, so let’s keep on developing scientific solutions for life on earth rather than rush to send a select few humans on a voyage that can be better done with future technology.

  2. Was a good read until you dripped the old “why don’t we focus on feeding the poor” argument. THIS has been thoughouly debunked.

    “Not convincing, as there are so many other technical challenges we could, and have, set ourselves to overcome, like putting an end to climate change, or to hunger. ”

    Anyone who uses this argument has zero understanding of how space exploration (and charity) is funded.

    Hint: Lockheed Martin aren’t involved in anti-hunger programs.

    Space money and food money don’t come from the same pot.

    In addition, there are countries without manned space programs that still have food shortages. The question of hynger has existed since the dawn of man.

    To think that throwing 100 billion dollars at the problem and having it magically disappear is deluded, to put it mildly.

    In fact, I’m pretty sure over the lifetime of this species, we have already spent that…. Yet we still have hunger. What a coincidence. And by the way, soace research actually contributes to feeding the planet. Yes, “precision farming” is a thing. And it’s being practiced in India right now, where space assets are helping to boost crop yields by 200% and more.

    Your myth just got BUSTED.

    And seriously…. How can you suggest that we would be better off “solving world hunger” and then end the article with “let’s build a Moon base”?

    How many must continue starving just so we can send an elite select few to the Moon?

    I jest of course. I favour the Moon base too. Im just highlighting the fact that the “global hunger” argument falls to pieces very easily.

  3. I’m no expert on any of this. This is just one simple minded man’s opinion. The potential advantages outweigh the definitive disadvantages. It’s that simple. We need more visionaries like Musk rather than naysayers. Why not a moon base and go to Mars? Why does it have to be one or the other?

  4. A) “Thousands of billions” and “one thousand billions” is not correct. It is correctly said as “trillions.”B)
    B) NASA has almost completely lost interest in the moon. When was the last time we sent anyone to the moon? 1972. Do we have enough time to win President Bush’s (I don’t remember which Bush) challenge to reach the moon again by 2020? Probably not.
    C) Maybe we could just wait for newer tech and then terraform Mars? How many books, movies, and TV shows have included terraformed planets in the future? A lot. Maybe we are an alien race that terraformed Earth and moved here. I’m just saying. I’m not asking for backlash from people that don’t believe in aliens.
    D) If we somehow manage to get time travel before setting foot on Mars, we could bring the time machine to Mars and use it to live in pre-historic Mars.

  5. im trying to do an argumentative essay about how we SHOULD go to mars. This messed up my thoughts and made me wonder. thanks.

  6. Why does it matter if there is life on Mars or not? If there is only microbial life sure it will be interesting, but at the end the day the supremecy of man should reign supreme. Understanding the origin of life wouldn´t help as many people as the technological innovation from a Martian colony would. Besides earth life if far superior to martian life (if it exists) we should just let natural selection take over on mars and maybe the planet would go green rather than red.


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