Scientists who observe the planet Mars received a remarkable Christmas present last year.
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On December 24, 2021, a meteorite hit its surface, causing tremors of magnitude 4.
These were detected by the Insight probe and its seismometer, which landed on Mars almost four years ago, some 3,500 kilometers from the site of the impact.
But the origin of this Martian tremor was only confirmed in a second time, by the spacecraft called Mars Reconnaissance Orbiter (MRO). In orbit around the planet, it took pictures of the newly formed crater within 24 hours of the event.
The image is impressive: blocks of ice were thrown on the surface, and a crater about 150 meters in diameter and 20 meters deep was dug – the largest ever observed since the commissioning of the MRO orbiter, 16 years ago.
Even though meteorite impacts on Mars are not uncommon, “we never thought we would see something this big,” Ingrid Daubar, who works on the Insight and MRO missions, told a news conference on Thursday. .
The researchers estimate that the meteorite itself must have been around 12 meters, which on Earth would have led to it disintegrating in the atmosphere.
“It is quite simply the biggest impact of a meteorite on the ground that has been listened to since we have been doing science with seismographs or seismometers”, explained to AFP Philippe Lognonné, professor of planetology who participated in two studies from these observations, published Thursday in the journal Science.
An audio recording of the quake, obtained by accelerating the vibrations collected by the seismometer to make them audible, was released by NASA.
“Useful” ice cream
The valuable information collected should make it possible to refine our knowledge of the interior of Mars and the history of its formation.
The presence of ice, in particular, is “surprising”, underlined Ingrid Daubar, also co-author of the two studies. “It’s the hottest spot on Mars, closest to the equator, where we’ve seen ice.”
In addition to the scientific interest of this discovery for the study of the Martian climate, the presence of water at this latitude could prove “very useful” for future explorers, said Lori Glaze, director of planetary sciences at NASA.
“We would like to land astronauts as close to the equator as possible,” she said, due to warmer temperatures. However, the ice present on site could then be transformed into water or oxygen.
The impact of the meteorite was powerful enough to generate both body waves (propagating to the core) and surface waves (crossing the planet’s crust horizontally), thus making it possible to study in detail the internal structure of Mars.
The crust on which Insight is located was thus found to be less dense than that traversed from the site of the collision.
In addition, the current models “on the deep structure of the mantle of Mars will deserve to be reanalyzed a little” in the light of these data, explained Philippe Lognonné, of the Institute of Physics of the Globe in Paris.
As expected, the Insight probe is now operating in slow motion due to dust that has accumulated on its solar panels. Contact will likely be lost within “about four to eight weeks,” said Bruce Banerdt of NASA’s Jet Propulsion Laboratory on Thursday, who said he was “sad” but welcomed the mission’s success.
Insight has detected more than 1,300 “Marsquakes” in total – including some caused by smaller meteorites – and the data collected will be used by scientists around the world for years to come.
