Space. This Mars meteorite that tells us about the formation of the Earth

What secrets does she have? Scientists have recently identified the origin of a Mars meteorite, which they consider an “open book” about the first moments of the planet Mars. The object from the red planet is potentially rich in lessons about the formation of the Earth.

“Black Beauty”, NWA 7034 with its nickname, has fascinated geologists since its discovery in the Sahara in 2011.

The “oldest” Mars rock

This block, which is easily held in the hand and weighs a little over 300 grams before being cut, is “the oldest stone we have, whether it is on Mars, but also almost on Earth”, planetologist Sylvain Bouley explained to AFP, who co-signs the published study. Tuesday i Nature communication on this subject.

It contains zircons, a kind of mineral, dated to 4.48 billion years old. Or “about 80 million years after the beginning of the formation of the planets” in the solar system, continued Sylvain Bouley, professor at the Geosciences Laboratory at the University of Paris-Saclay.

NWA 7034 is thus an “open book about the first moments of Mars”, when its magma surface began to solidify. While we have “lost this primitive story of our Earth”, where most of the original lands have disappeared, in the great reworking of plate tectonics – a phenomenon that has largely spared Mars.

A crater located in the southern hemisphere of Mars

The team of scientists, led by planetary scientists from Australia’s Curtin University in Perth, with a strong contribution from French institutions, succeeded in determining the exact origin of the meteorite in a region that houses a very primitive crust from the red planet.

He had to identify a crater formed by the impact of a meteor coming from space with “sufficient force to push rocks out at very high speeds, more than 5 km / s, to escape the gravity of Mars”. , Anthony Lagain explains to AFP. scientist at Curtin University and first author of the study. Such craters must be at least 3 km in diameter. Problem, Mars has about 80,000 of at least this size.

Second clue, scientists knew that NWA 7034 had been thrown into space about five million years ago, thanks to the measurement of its exposure to cosmic rays. “So we were looking for a very young and large crater,” says AFP Anthony Lagain, whose doctoral dissertation focused in particular on the dating of Mars craters.

Another clue, the analysis of the composition of “Black Beauty” revealed that it had been brutally heated 1.5 billion years ago, probably by an asteroid impact. In other words, the stone was first pulled out of the surface before falling further, where another impact this time threw it into space, all the way to Earth.

Armed with this information, Anthony Lagain improved a crater detection algorithm developed at Curtin. Before he got him to paint with a supercomputer the mosaic of 90 million images of Mars craters, accumulated thanks to the camera from a NASA satellite.

The result narrowed the election to 19 pits and then only one, Karratha. This 10 km diameter crater is located in “a very ancient region of the southern hemisphere, rich in potassium and thorium, like Black Beauty”, says Anthony Lagain. Final argument, the meteorite is the only one of the Martians that is highly magnetized, but “the region where Karratha is located is the most magnetized on Mars”.

“Understand what happened in the beginning”

Spread across the Terra Cimmeria and Sirenum regions, this area is “probably a remnant of the oldest crust on Mars,” according to the study. Who requests to send a mission dedicated to the study of its geology.

Professor Bouley points to a kind of “bias” that focused the Mars missions on the search for traces of water and life, at the expense of past times that may have allowed their appearance. Moreover, NWA 7034 after its discovery had come on the front page due to the presence of water in it.

But to understand the formation of the first planetary crusts is to understand what happened in the very beginning, Anthony Lagain recalls, and “how we arrive at a planet as exceptional as the Earth in the universe”.

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