Perseverance failed to detect biosignatures on the surface of Mars, the study found

Illustration de Perseverance sur Mars. © Tryfonov, Adobe Stock

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[EN VIDÉO] Perseverance, in search of life on Mars Perseverance, this is how NASA has decided to name the rover it will send to Mars in the summer of 2020. A rover from which researchers expect a lot. It will be the first to collect rock samples to return to Earth. Objective: Find traces of microbial life. This is one of the main missions of the Perseverance rover: to find traces of life in the rocks of the Martian soil, or at least try to. Because it is not fossils of organisms that Perseverance is looking for, but molecules, more or less complex, that would have been synthesized by biological processes. The Curiosity rover would have taken the first step by confirming the presence of organic molecules (compounds of methane and carbon) on Mars. If Perseverance managed to find more complex biomolecules, it could mean that the planet would have experienced the beginnings of even very rudimentary organic life. A rather exciting prospect! The problem of UV radiation This target is also one of the next rover that should reach Mars: Rosalind Franklin. This new rover from the ExoMars program of ESA and Roscosmos will carry a set of instruments on board with the aim of performing Raman spectroscopic measurements. Raman spectroscopy is a method of chemical analysis that identifies the structure of the molecules present in a sample. This type of instrument already equips the Perseverance rover. If this method is effective on Earth, and widely used to detect biomolecules, things seem complicated on Mars, because there is a big difference between Mars and Earth: the atmosphere. Yes, Mars has one, but it is much thinner than Earth’s. However, the Earth’s atmosphere plays an essential role in the preservation of life: it stops a large part of ultraviolet radiation (UVR), which is harmful in high doses to living organisms. Is this method of analysis the most suitable for perseverance? do biomolecules remain stable under the fire of solar radiation impacting the Martian soil? Some pre-mission studies have shown that, while the rate of degradation is certainly very high in the first few centimeters of the surface, the regolith nevertheless had the ability to protect certain biomolecules. Considering this hypothesis, however, there is another problem, linked this time to the method of analysis. In fact, if the scientists showed that biomolecules could remain detectable despite the atmospheric conditions of Mars, these tests had not been done using Raman spectroscopy to make the analyses, which is why a team of researchers has come to question the analysis ability of this type. instrument in Martian conditions. Thus, a series of experiments (Biomex) were carried out on board the International Space Station. Seven different types of biomolecules were exposed to solar radiation outside the station for 469 days. They were mixed with analogues of the Martian regolith in order to better simulate the environmental conditions prevailing on the red planet. The samples were then analyzed with Raman spectroscopy. The regolith signal overlaps with that of biomolecules. , the signal associated with regolith minerals partially cover or even completely mask the signal associated with biomolecules. For example, the particularly strong signal of hematite, a mineral very present on Mars, falls exactly in the same range of values ​​as that of chlorophyll, cellulose or other biomolecules, preventing their detection. Samples containing a lot of clay proved even more difficult to analyze. However, this mineral is considered to be the matrix most likely to have preserved organic molecules on Mars. This study, published in Science Advances, shows the difficulty of analyzing samples containing mineral phases using Raman spectroscopy, in the presence of high exposure to UV radiation. On the other hand, samples located in depth and therefore more protected from UV radiation could remain correctly detectable with this method. Perseverance, which can only analyze surface samples, could therefore completely miss a biosignal, until and all if there were biomolecules really present in those analyzed. show! Drilling deep, Rosalind Franklin’s solution. All hopes therefore turn to the Rosalind Franklin rover, which will have the ability to drill up to 2 meters deep to recover UV-protected samples. A modification of the Raman spectroscopy analysis technique also shows good results on Earth. , but the equipment still needs to be miniaturized before it can be integrated into a possible mission to Mars. Meanwhile, a new approach to data processing could nevertheless allow some information to be extracted from the samples analyzed by Perseverance. Otherwise, we’ll have to wait for the samples to return to Earth, scheduled for 2033. Interested in what you just read?
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