Looking for Life on Mars: Beware of False Fossils!

Thanks to the latest explorations on Mars, we now know that the planet must have been habitable some 4 billion years ago when it was covered by a vast ocean of liquid water. And since March 2020, the Perserverance rover has been on the lookout for more recent signs of life that can be found thanks to samples from Martian rocks.

That’s why it’s important to be able to definitively identify what a fossil is, then translate that to evidence of life, what it looks like but isn’t. A team of scientists from the University of Edinburgh observed this in a study published in the journal Science on November 16, 2021. Journal of the Geological Society, By listing the actual biosignatures and the processes that may have led to their imitation, they have thus listed a large amount of criteria for identifying a true fossil, and distinguishing it from something that resembles it. .

“At some point, a Martian rover will be found very probably Something that resembles a fossil is therefore essential to being able to confidently distinguish them from structures and substances created by chemical reactions. For every type of fossil, there is at least one non-biological process that creates very similar things, so there is a real need to improve our understanding of their formation”. Notes Dr. Sean McMahon, the study’s first author and researcher in Astrobiology at the University of Edinburgh.

How to distinguish truth from falsehood?

Unlike tests for COVID-19, the researchers emphasized the low chance of false negatives, rather than worrying about false positives. As they explain in their study, the processes that “Copy” are mostly”Kinetic processes far from thermodynamic equilibrium, often in the presence of liquid water and organic matter, conditions that could actually give rise to and promote life.”

According to him, not only can abiotic processes (without the presence of life) mimic the morphological biosignature, i.e. they may have the same external appearance, but they may also have the same chemical, molecular, mineral, isotopic characteristics or even real There may also be a texture compared to a fossil. , What has misled them! Thus, whatever criteria are used to identify proof of life will not in itself be the determining factor and many of them will have to be compiled.

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In particular, a key element of life, water, can generate several false biosignatures: the team focused on the interaction between the large amounts of water present on the Red Planet and basalt lava. Thus many false evidences have been identified, such as “hard crystalline (Micro Crystals, Editor’s Note), Weathering texture, Production of mineral ‘seed’ from chemical gardens (The mineral composition is reminiscent of plant forms, editor’s note) and production of silica-rich alkaline fluids that can generate biomorphs (which look like living forms, editor’s note)”, As the study suggests.

Places where life is at its best can be full of pitfalls

In addition to identifying the various materials and chemical processes that lead to false evidence of life, the researchers asked themselves the question of the place: where should we prioritize looking for life? In their study, they emphasize that there will be abiotic material that mimics fossils.produced by energy dissipation, in systems characterized by strong thermodynamic or chemical gradients, and Through presence of liquid water. , Thus, environments conducive to the origin and maintenance of life may also, by their very nature, be conducive to the formation of false biosignatures.

The researchers then concluded that a potential biological material that is unlikely to support life, for example a cold desert, would be more likely to be true evidence of life than the same material found in an area where life is more abundant. is or is likely to exist. Therefore he argues that “IThe search for evidence of life should not be focused solely on the environments where life is most likely to arise because this is where the evidence will be most ambiguous.”

The search for life on Mars has begun

The study concludes that “Inorganic organic matter may have changed on Mars Located on the way of life, but without Never reach this destination”Hence the high amount of false evidence of life. But the Persistence rover hasn’t said its last word, and continues its journey to Mars. There are other projects underway to join them, and support the search for traces of life on the Red Planet, and after this study, may be better informed.

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In particular, the future Rosalind Franklin rover, which should fly in the fall of 2022 as part of the “ExoMars” mission, will carry with it a drill capable of extracting samples 2 meters below the surface, where organic molecules are preserved. can go. Oxidation or radiation damage. The Persistence rover is not capable of such a feat, but it is nonetheless capable of storing a good amount of promising geological samples and sealing them for keeping until they are returned to Earth. So both will be complementary.

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