Paris (AFP)

In fifteen months of presence on Mars, the InSight robot and its seismograph have already detected nearly 500 quivers from the bowels of the red planet, an abundant harvest that provides a portrait of a "living planet", shaken by numerous earthquakes.

"It is always moving to imagine this instrument on Mars which sends us these data", confides to AFP Philippe Lognonné, researcher of the Institute of Physics of the Globe of Paris and father of SEIS, the French seismograph embarked by InSight .

After 6 and a half months of space travel and 480 million kilometers traveled, the NASA probe had landed with great fanfare in the Martian plain of Elysium, in November 2018, allowing humanity for the first time to stick his ear to the ground of the planet.

And since then, the planet has been rather talkative: "As of September 30, 2019, InSight has detected 174 seismic events, of which 24 are relatively large (with a magnitude between 3 and 4)", say the authors of six published studies Monday in Nature Geoscience and Nature Communication, international work involving more than one hundred and fifty researchers.

For Charles Yana, SEIS project manager at the French space agency Cnes, "the number of these detections is quite surprising because the models did not estimate as much".

"And since September, it continues," notes Philippe Lognonné. The seismograph now displays on the counter no less than 460 detected events of which forty are most likely due to earthquakes, "earthquakes associated with playing faults", as the geophysicist describes them.

Two of them come from a volcanic region, located 1,600 km from where InSight landed, called "Cerberus Fossae" and made up of canyons more than a thousand kilometers long in which lava flowed. "In this area, things are moving in depth!" Enthuses Charles Yana.

NASA had put online in October the sound files of these two tremors (dating from May 22 and July 25), "slightly" processed and accelerated to become audible to Earthlings.

- Pending a bigger earthquake -

The origin of the 420 other quivers is less clear: small very superficial earthquakes, micro-landslides, landslides of cliffs ... Difficult to decide. "And" certain signals are complicated to understand because it is the first time that we see them, "notes Philippe Lognonné.

Anyway "these results (...) reveal a living planet", welcomes the Cnes, prime contractor of SEIS, in a press release.

The data from the InSight mission allows us to learn a little more about the composition of the red planet. Seismic waves, varying according to the materials they pass through, offer a picture of the bowels of the planet.

Scientists were able to determine that the first 10 kilometers of the Martian crust, the result of very old lava flows, "have been altered by several billion years of geological activity, impact, or by ancient circulation processes. of water ", notes Philippe Lognonné.

But researchers are still waiting for the Grail, an earthquake of magnitude equal to or greater than 4. The waves would then propagate more deeply and could give much more information on the internal structure of the planet (lower mantle and nucleus). "This is the tastiest part," says Bruce Banerdt, InSight scientist at Nasa's JPL laboratory in Pasadena, California.

Knowing the composition of the red planet will indeed help to understand how it formed and why the water of its lakes and rivers evaporated about 3.5 billion years ago.

"We are a bit hungry," admits Philippe Lognonné. "But it's not over!" If the mission was initially budgeted by NASA for only two years, Charles Yana is hopeful that it will be extended in view of the "good results" already collected.

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