Since the discovery of the toxic perchlorate being globally distributed in the martian soil the chances for microscopic life there are thought to be greatly reduced..
Even in the RSL's, once thought to be avoided for fear of contamination by the Curiosity rover, signs of perchlorates were spotted.
Over 40 diverse microorganisms capable of growth via perchlorate reduction have been isolated. They use 2 types of enzymes that collectively take perchlorate into harmless chloride, while free oxygen is generated.

In a protected environment, like a greenhouse, those microbes could be used to clean up soil and dust that would then be suitable for agriculture and would also help in creating a breathable atmosphere.
Outside that protected environment the microbes would barely have a chance to survive the harsh martian conditions so contamination seems out of the question.

Although planetary protection rules forbid biological contamination of Mars, could not nevertheless perchlorate consuming bacteria be introduced there, at least for controlled tests ?
Because the introduced microbe would be well examined, it could always be well distinguished from whatever martian microbe would appear.

And how could a toxic consuming species, producing only harmless chloride and oxygen escaping in the atmosphere, be a threat for potential life forms native to Mars?

  • 8
    $\begingroup$ Oxygen isn't harmless. The Great Oxygenation Event may have caused the extinction of most of the life on Earth 2.5 billion years ago, and if current Martian life exists (admittedly a big if), it already has mechanisms to deal with or avoid the pervasive perchlorates, and the lack of molecular oxygen in the atmosphere. $\endgroup$
    – notovny
    Commented Sep 30, 2019 at 18:49
  • 3
    $\begingroup$ Before testing a microbe on Mars, tests under simulated marsian conditions should be done on Earth. Microbes that don't survive simulated environments need not to be sent to Mars. $\endgroup$
    – Uwe
    Commented Oct 3, 2019 at 14:41
  • 2
    $\begingroup$ While there are microorganisms that can survive a shorter or longer period in Mars conditions in endospore form (dormant), AFAIK nothing approaches actively living (gathering nutrients, reproduction, growth) there. $\endgroup$
    – SF.
    Commented Jul 26, 2021 at 10:20
  • 3
    $\begingroup$ The perchlorate-eating microbes can survive in Mars soil, but not in mars atmospheric pressure or humidity levels or (mostly) temperatures. If released in "the wild" they will almost instantaneously expire. So your answer is "not at all, absolute zero. At worst they would contaminate biological detection markers when we seek for original Mars life" $\endgroup$ Commented Jul 26, 2021 at 11:08
  • 3
    $\begingroup$ @PcMan where did you get that idea? Perchlorate salts tend to be very highly soluble, calcium perchlorate is actually deliquescent. Some plants accumulate perchlorate, but it is generally not particularly toxic to them. In mammals, sodium perchlorate is a little more toxic than table salt and the perchlorate ions are excreted rapidly with a biological half life of 6-8 hours, the main hazard being long-term exposure with it interfering with iodine uptake by the thyroid. $\endgroup$ Commented Jul 26, 2021 at 17:14

1 Answer 1


There are a number of issues that I can envisage.

Chemical reaction rates can be temperature dependent: the colder the temperature the slower the rate of reactions. This applies to life forms.

The cold temperatures on Mars could result in microbes having a slower "metabolism" and the rate of perchlorate consumption could be slower than envisaged.

Like all known life forms, microbes require water (moisture) to survive. The two things that Mars currently lacks is warm and moisture and microbes depend on both to flourish. For your plan to succeed it would need a mixture of perchlorate "rich" regolith, moisture, microbes and warmth.

You may need to undergo a process of doublethink for what comes next.

The second issue is any microbes introduced to Mars could be an exotic species. The history of exotic species on Earth is they are rarely, if ever contained, and usually become problematic. They can out compete native species and become dominant, to the detriment of native species. The same could happen on Mars. I place little faith in anyone's abilities to force the containment of microbes, or any other introduced species on Mars.

The other thing about exotic species, is in their natural habitat they usually have predators, even microbes. Place them in an environment without predators and they can become invasive, to the detriment of native species.

The other problem I envisage is, assuming everything works as planned, the chloride products produced by the microbes would be another problem as most agricultural plants have a low tolerance for salt and other chlorides.

  • 1
    $\begingroup$ Only some fruits are shown fot low tolerance of chlorides. And from what I could find,, on Mars it's mostly calcium perchlorate, so no problem with too much sodium. $\endgroup$
    – Cornelis
    Commented Jul 27, 2021 at 17:56
  • 3
    $\begingroup$ It seems highly unlikely that any introduced Earth species would be capable of out competing the local inhabitants that would have adapted to the environment over a very extended period of time. This is especially true given the great difference in environment such as no moisture, no oxygen, near vacuum, intense UV light and very low temperatures. Much more likely the Earth based microbes would loose out to the competition in much the same way that Martian microbes would here. $\endgroup$
    – Slarty
    Commented Jul 27, 2021 at 21:49
  • 1
    $\begingroup$ And CaCl2 is used as a food additive ! ;) $\endgroup$
    – Cornelis
    Commented Jul 27, 2021 at 21:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.