Slowly but surely, Mars reveals its intimacy. 943 “soils” (or Martian days) after its spectacular landing on November 26, 2018 in the heart of the Elysium Planitia plain, NASA’s InSight mission, devoted to Martian seismology, announces a breakthrough in the knowledge of the sub- ground of the red planet.
In three articles published Thursday, July 22 in the journal Science, the team of the French seismometer SEIS (for Seismic Experiment for Interior Structures), manufactured with the help of Switzerland, explains how it used the seismic signals produced by a dozen Martian earthquakes to probe the inner layers of the star. Core, mantle, crust… Mars turns out to have an internal structure quite different from that of Earth.
The depths of a planet are a reflection of its origin and its evolution. Its inner layers can deliver information on its formation conditions in the early solar system as well as on its geomagnetic and geological activity, past and present. At least when we manage to characterize them with precision. What, for the moment, has been achieved only for the cases of the Earth and the Moon by studying, thanks to networks of seismometers, the way in which the seismic waves propagate and are reflected in the subsoil at the time earthquakes.
Hence the interest of the InSight mission. This consisted in placing on the ground of Mars a geophysical station equipped with a seismometer. Then to try to detect using this unique instrument – designed by the Institut de physique du globe de Paris (IPGP) under a CNES project management, in collaboration with several French, British, German and French laboratories and industrialists. Swiss – earthquakes in order to access better estimates of the internal composition of Mars. A real challenge because if, on this planet devoid of plate tectonics, earthquakes are relatively frequent, they are of low intensity. And in practice, only a handful of them are able to generate the right signals.
This is the feat that the SEIS team achieved by analyzing the seismic waves produced directly or indirectly by around ten of these events. The result ? He shows that while being close to that of Earth, the internal structure of Mars presents peculiarities that could be used to explain its disastrous evolution towards a dry, cold, devoid of atmosphere and geologically moribund world.
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