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

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

UPGRADE DAY

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

“Black Beauty”, NWA 7034 of its nickname, has fascinated geologists since its discovery in the Sahara in 2011. This block, easily held in the hand and weighing just over 300 grams before cutting, is “the the oldest rock we have, whether on Mars but also almost on Earth,” planetary scientist Sylvain Bouley, who co-authored the study published in Nature Communications, told AFP.

It contains zircons, a kind of mineral, dated at 4.48 billion years old. Or “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 the original lands have disappeared, in the great reworking of plate tectonics – a phenomenon that has largely spared Mars.

The team of researchers, led by planetary scientists from the Australian 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 very primitive crust of the red planet.

He had to identify a crater, formed by the impact of a fireball from space with “sufficient force to eject the rocks at very high speed, more than 5 km/s, to escape 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 five million years ago, thanks to measuring its exposure to cosmic rays.

90 million photos of craters

“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, probably 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.

Fitted 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 just 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 “probably a relic of the oldest crust on Mars,” according to the study. Who pleads for the sending of a mission dedicated to the study of its geology.

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

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