Has Mars ever supported life? If the answer to this question is still hidden in the red soil of the planet, a team of researchers has nevertheless made an interesting discovery. 3.6 billion years ago, the Martian climate alternated between dry and wet seasons. A feature that turns out to be quite favorable for the synthesis of complex organic molecules!
The more time passes, the more evidence accumulates for the past existence of seas, lakes and rivers on the surface of Mars. These environments have indeed left many traces in the Martian landscape: channels, sedimentary deposits or erosion surfaces are all witnesses that tell us that the Red Planet once presented favorable conditions for habitation with the presence of water. liquidliquid On the surface, in which life could potentially develop.
Organic Molecules: The Difficult Question of Biological or Abiotic Origin
yet irrefutable evidence ofEvolutionEvolution A form of life, even extremely primitive, is still pending, although the clues are slowly accumulating. CuriosityCuriosity at PerseverancePerseveranceBoth RoversRovers In present-day activity on the planet’s surface as well, the two have thus detected signatures of organic molecules in some Martian rocks. The discoveries are promising and encouraging, but not enough to confirm that life could have existed on Mars several billion years ago. because if moleculesmolecules Organisms can be signatures of some past biological activity, they can also be completely abioticabiotici.e. is formed by chemical reactions between mineralsminerals Without interference from any form of life, within a hydrated medium.
While waiting for observations that would make it possible to definitively dispel doubts on the origin of these molecules, research continues, especially on the characterization of the past atmosphere of Mars. Because the formation of complex organic molecules, the precursors of life, requires certain environmental conditions. Of course liquid water, but is it sufficient to initiate and promote the spontaneous arrangement of these types of molecules? presence of season’sseason’s And a certain periodicity in the hydrological cycle also seems to be an important parameter. However, these points were still poorly constrained… until now.
Hexagonal pattern that says a lot about Mars’ hydrologic cycle
Because the Curiosity rover brings particularly interesting new observations made at Gale Crater. This is by studying a 3.8 to 3.6 billion year old sulfate rich sedimentary unit that NASANASA Made this amazing discovery. photographsphotographs In fact a floor consisting of a hexagonal pattern is revealed.
Everyone on Earth has certainly already seen very geometric structures of this type called desiccation cracks (or polygons), which form sedimentsediment The soils of the smaller basins are subject to drying seasonally. For the team of researchers led by William Rapin, the observations made by Curiosity would be nothing more than evidence of someone’s past existence. climateclimate Mars is characterized by a cyclical, regular alternation of dry and wet seasons. The index of this cyclicity will be given by the size of the junctions between the polygons. While drying cracks initially form T-junctions, repeated drying will mature polygons, whose junctions will then arrange themselves into Y-junctions. And this is what has been observed on Mars. Laboratory experiments further indicate that a minimum of 10 drying cycles are required to achieve this drying polygonal shape.
Favorable cyclization for the synthesis of prebiotic molecules
published in the journal NatureTherefore, the discovery of this periodicity in the hydrological cycle of Mars is particularly important, and this is for several reasons. The first is that it invalidates the hypothesis that the crater’s fluvio-lacustrine activity would be associated only with the impact ofasteroidasteroid Or for a specific and time bound volcanic event. On the contrary, it suggests more stable and permanent hydrological processes, similar to those observed on Earth. Second, the frequent alternation of dry and wet seasons appears to be a necessary element to consider in chemical evolution. prebioticprebiotic, Indeed, during the events of DryDryEvaporation of the water will concentrate the soluble elements in the residual liquid, increasing the rate of chemical reactions and therefore increasing the likelihood of obtaining complex organic molecules nucleotidenucleotide, In particular, it has been demonstrated in the laboratory that the reactions of polymerizationpolymerization needed to build molecules arnarn Or d nd n for the passage of nucleotides from, oramino acidsamino acids To proteinproteinessential steps of dehydrationdehydration, Conditions are favorable in terms of cyclicity of dry and wet periods. Finally, chemical analysis performed by the ChemCam instrument shows that the sediments in question are rich in sulfates, salts that form crystals when water evaporates and have the ability to trap organic material and preserve it over geological time.
Favorable environment later than expected?
Everything therefore suggests that Gale Crater may have presented optimal conditions for the synthesis of prebiotic molecules necessary for the evolution of primitive life forms around 3.6 billion years ago. These results indicate, as the authors of the article point out, that the most favorable period for the emergence of life would have been around the Noachian–Hesperian transition. Until now the older and wetter period of the Noachian was preferred.
Beyond the issue of possible life on Mars, these results allow us to better understand the conditions for life to appear on Earth. because unlike Mars, whose surface porteporte There are still geological traces several billion years old, the tectonics of terrestrial plates have completely erased these witnesses of the beginning of life on our planet.
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