Microbes could have changed the climate of Mars 4 billion years ago

According to a modeling study published in Nature Astronomy, it is highly likely that the subsurface of the planet Mars was habitable for microorganisms that feed on hydrogen and produce methane. The predicted biomass production may have been comparable to that of Earth’s early ocean. This large biosphere may have had an overall cooling effect on Mars’ early climate, possibly ending the planet’s habitability.

The potential habitability of the planet Mars more than 3.7 billion years ago has been the subject of much debate. Evidence suggests that the Red Planet hosted, at least for part of its history, conditions potentially favorable for the development of life. However, the likelihood of such a scenario has rarely been established quantitatively.

A scientific team – led by Régis Ferrière (IBENS and head of the “iGLOBES” international laboratory of the CNRS and ENS-PSL at the University of Arizona) and Stephane Mazevet (OCA) and which brings together researchers from the ENS -PSL and LESIA (CNRS, Observatoire de Paris-PSL) – modeled the interaction between the primitive environment of Mars and an ecosystem of methanogenic hydrogenotrophs (microorganisms that survive by consuming hydrogen and producing methane) which are considered to be among the first forms of life on Earth. The authors’ simulations predict that the Martian crust was a viable place for this ecosystem – provided the surface was not entirely covered in ice – and could have accommodated biomass production similar to that of Earth’s early ocean. The team predicts that this ecosystem would have triggered a mutual feedback with the climate, causing a global cooling of 40 degrees and creating less habitable conditions closer to the surface. This would have forced these primitive metabolisms to sink deeper and deeper into the crust, perhaps causing their own demise if no other internal energy source was accessible to them. Looking ahead, the authors identify three sites, Hellas Planitia, Isidis Planitia and Jezero Crater, as the best places to look for signs of this early methanogenic life near the surface of Mars.

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