Almost a year and a half after landing on Mars on February 18, 2021, in the Jezero crater, NASA’s Perseverance rover has already traveled more than 12 kilometers on the surface of the Red Planet, taken more than 300,000 images and launched a quantity of analyses. Some results have already been unveiled, such as the first Martian sounds or confirmation that Jezero had once hosted a lake as large as Lake Geneva, but we expected more. In particular on the geology of the region, supposed to have been conducive to a possible appearance of life, at the distant time when Mars was not the arid and cold star that it has become. This wait ended on August 25 with the simultaneous publication, in the journals Science and Science Advancesof four studies concerning the Martian subsoil.
“This is the first package of geological publications, summarizes Sylvestre Maurice, astrophysicist at the Institute for Research in Astrophysics and Planetology, whose team provided the SuperCam instrument for Perseverance, and co-author of two of these studies. The instruments together deliver their verdict. » And this verdict is above all that of a surprise. “Reading the results surprised us, continues the French researcher: Mars is imaginative, in the sense that Earth paradigms don’t necessarily work on this other planet. »
“It is the expression of a geology different from what is happening on our planet” Sylvestre Maurice, astrophysicist
In this bottom of the crater which was once (3.4 to 3.7 billion years ago) covered by a lake, planetologists expected to see sedimentary rocks. It was missed: Perseverance detected igneous rocks containing olivine, a mineral that, on Earth, is found in abundance in the mantle. On our planet, one would assume that these rocks formed at depth rose to the surface by taking advantage of plate tectonics. Easy. Boredom, emphasizes Sylvestre Maurice, “is that there is no plate tectonics on Mars”.
Geologists must therefore imagine other scenarios, over interminable periods, with significant phases of erosion stripping the surface layers and revealing the buried rocks. “It betrays a long and complicated history, explains Sylvestre Maurice, it is the expression of a geology different from what is happening on our planet. And it feels good to get out of this box that is Earth, to show us that there are other possibilities. »
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