A Martian meteorite rich in lessons on the formation of the Earth

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A Martian meteorite rich in lessons on the formation of the Earth

The Martian meteorite NWA 7034, nicknamed “black beauty”, weighs 320 g. It was discovered in the Sahara Desert.

Scientists have identified the region of origin of a Martian meteorite, an “open book” on the first moments from the planet Mars, potentially rich in lessons on the formation of the Earth.

Beauté noire (Black Beauty), NWA 7034 of its small name, has fascinated geologists since its discovery in the Sahara in 2011. This block, easily held in the hand and weighing 320 grams, is the oldest rock we have, whether on Mars , but also almost on Earth, told AFP planetary scientist Sylvain Bouley, who co-signed the study published in Nature Communications.

It contains zircons, a kind of mineral, dated at 4.48 billion years old. That is about 80 million years after the start of the formation of the planets of the solar system, says Mr. Bouley, professor at the Geosciences laboratory of the University of Paris-Saclay.

NWA 7034 is thus an open book on the first moments of Mars, when its magma surface began to solidify. While we have lost this early history of our Earth, where the majority of original terrain has disappeared, in the great reworking of plate tectonics – a phenomenon that has largely spared Mars.

The team of researchers, led by planetary scientists from Australia's Curtin University in Perth, with a strong contribution from French institutions, succeeded in the feat of determining the precise origin of the meteorite, in a region hosting a crust very primitive from the red planet.

He had to identify a crater, formed by the impact of a bolide coming from space with enough force to eject the rocks at very high speed, more than 5 km/s, to escape the Martian gravity, explains to AFP Anthony Lagain, planetary scientist at Curtin University and first author of the study.

Such craters must be at least 3 km in diameter. Problem, Mars has some 80,000 at least this size.

Second clue, the researchers knew that NWA 7034 had been ejected into space about 5 million years ago. years, thanks to the measurement of its exposure to cosmic rays.

We were therefore looking for a very young and large crater, tells AFP Anthony Lagain, whose doctoral thesis focused in particular on the dating of Martian craters.

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

With this information, Anthony Lagain improved a crater detection algorithm developed at Curtin. Before making him grind with a supercomputer the mosaic of 90 million photos of Martian craters, accumulated thanks to the camera of a NASA satellite.

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

Extended over the regions of Terra Cimmeria and Sirenum , this area is likely a relic of Mars' oldest crust, according to the study, which argues for sending a dedicated mission to study its geology.

Professor Bouley points to a kind of bias, which focused the Martian missions on the search for traces of water and life, at the expense of previous times, which may have allowed their appearance. Moreover, after its discovery, NWA 7034 made headlines because of the presence of water in it.

However, understanding the formation of the first planetary crusts is understand what happened at the very beginning, recalls Mr. Lagain, and how we arrive at a planet as exceptional as the Earth in the Universe.

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