Illustration de Perseverance sur Mars. © Tryfonov, Adobe Stock

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

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[EN VIDÉO] Perseverance, in search of life on Mars
Perseverance, this is how NASA has decided to name the rover that it will send to Mars in the summer of 2020. A rover that researchers expect a lot from. He will be the first to collect rock samples to bring back to Earth. Objective: find traces of microbial life.

Is one of main missions of the Perseverance rover : find traces of life in the rocks of the Martian soil or at least try. Because they are not fossils…” data-image=” ” data- url =”” data-more=”Read more”>fossils organizations you are looking for Perseverancebut the so-called single covalent bond…” data-image=”” data-url= ” https: //” data-more=”Read more”>molecules, more or less complex, which would have been synthesized by biological processes. The Wanderer Curiosity 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 had experienced the beginnings of even very rudimentary organic life. Quite an exciting prospect!

The problem of ultraviolet radiation

This target is also one of the next rover to join Mars: Rosalind Franklin. this new rover of the ExoMars program of ESA and Roscosmos It will carry on board a suite of instruments to perform Raman spectroscopic measurements. the Raman spectroscopy is a chemical analysis method that identifies the structure of 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 to get more complicated on Mars.

Because there is a big difference between Mars and Earth: theatmosphere. If Mars does have one, however, it is much thinner than Earth’s. However, the Earth’s atmosphere plays an essential role in preserving life: it stops much of the radiation from ultraviolet (UVR), which are harmful in high doses to living organisms.

Is this method of analysis the most suitable for Perseverance?

Could biomolecules remain stable under fire from solar radiation hitting 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 nonetheless had the ability to protect certain biomolecules. Considering this hypothesis, however, there is another problem, this time linked to the method of analysis. In fact, if the scientists showed that the biomolecules could remain detectable despite the atmospheric conditions on Mars, these tests had not been done using Raman spectroscopy to perform the analyses.

For this reason, a team of researchers has come to question the analytical capacity of this type of instrument in Martian conditions. Thus, a series of experiments (Biomex) have been carried out on board the International Space Station (ISS), the only orbital station in service, representing a great step for…” data-image=”https:/ /cdn” data-url=” space-international-2571/” data-more=”Read more”>international Space Station. Seven different types of biomolecules were exposed to off-season solar radiation for 469 days. They were mixed with analogues of the Martian regolith to better simulate the environmental conditions prevailing on the Red Planet. The samples were then analyzed with Raman spectroscopy.

The signal from the regolith overlaps that of the biomolecules.

The researchers then realized that, during analyzes of samples most exposed to UVR (simulating those on the Martian surface), the signal associated with minerals the regolith partially covered or even totally masked the signal associated with the biomolecules. For example, the particularly strong signal from hematite, a mineral very present on Mars, falls in exactly the same range of values ​​as that of the chlorophyll, a polysaccharide made up of numerous glucose molecules linked by b-1,4-glycosidic bonds. It is a dietary fiber that is part of the structure of plants. It is not digested in the…” data-image=”” data-url=” https: / /” data-more=”Read more”>cellulose or other biomolecules, preventing their detection. Samples containing many particles
It is a particle whose size is less than 4 micrometers, whatever its mineralogical nature.
Clay is a mineral (more accurately a family…” data-image=” – 20.jpg” data-url=”” data-more=”Read more”>clay turned out to be 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 Progress of science, shows the difficulty of analyzing samples containing mineral phases using Raman spectroscopy, in the presence of high UVR exposure. On the other hand, samples located in depth and therefore more protected from UV radiation, could continue to be correctly detectable with this method.

Perseverance, which can only analyze surface samples, could miss a biosignature entirely, even if the biomolecules were actually present in the analyzed sample!

Deep drilling, Rosalind Franklin’s solution

Therefore, all hopes are directed to the Rosalind Franklin rover, which will have the ability to drill up to 2 meters deep to recover samples protected against UV rays.

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 potential mission to Mars. In the meantime, a new data processing approach could, however, make it possible to extract some information from the samples analyzed by Perseverance. Otherwise, you will have to wait. the return of the samples to Earthscheduled for 2033.

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