Arrived on Mars on November 26, 2018, NASA's InSight lander had given itself the main objective of auscultating the Red Planet. Its main instrument is indeed the SEIS seismometer (provided by France, thanks to the National Center for Space Studies), whose mission is to record Martian seismic waves in order to deduce the internal structure of the planet. But just as, with his stethoscope, a doctor does not just listen to the beating of the heart of his patients, the scientists hoped to detect these other cosmic events that are the falls of meteoroids. And they were not disappointed: in a study, published Monday, September 19 in Nature Geoscience, they announce that they have "heard" falling from the celestial rocks. Three exactly, in 2021.
Professor at the Higher Institute of Aeronautics and Space (ISAE-Supaéro, Toulouse) and first author of this article, Raphaël Garcia explains that SEIS is so sensitive that it has not only perceived the seismic waves linked to collisions , but also the acoustic waves produced by the arrival of meteoroids in the tenuous Martian atmosphere: “In one of the three events, we have the whole film. First, the entry of the meteoroid into the atmosphere, at several kilometers per second, creates a shock wave. Then, as it rubs a lot in the air and it heats up, the meteoroid breaks up between 13 and 16 kilometers in altitude, in a kind of explosion which releases a lot of energy. Finally, we have the pieces of rock that crash to the ground. » The device was even able to record echoes reflected off mountains or craters.
Brand new small craters
Armed with this data, the researchers calculated the probable place where these large stones of a few tens of kilograms had fallen and they asked the team of another NASA machine, the MRO orbiter, which revolves around Mars since 2006, to verify it by pointing its cameras at the areas in question. And bingo! Comparing them to old photographs taken by MRO, the new images showed the presence of small, brand new craters, only a few meters in diameter, surrounded by dark sheets - in reality dust and ground matter kicked up by the impact. A fourth event had been recorded, but, despite an extensive search, no crater was identified, likely because the meteoroid had disintegrated before reaching the ground.
This result is of interest to astronomers in more ways than one. First of all because it is the first time that, on another planet, the fall of meteoroids has been located using a seismometer. On our Earth, yet covered with these devices, this only happened once, in 2007, in Peru. In addition, having determined the exact location of the craters with MRO and their size allows to refine the models of the interior of Mars.
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