A meteorite reveals how planet Mars initially evolved

Although the exploration missions sent to the red planet have not yet allowed to bring samples of Martian rock, some have already reached us in the form of meteorites, that is, fragments of Mars expelled towards the space and that arrived on the earth.

The origin of these 400 kg of rocks collected worldwide was mainly determined thanks to the “rare gases that were trapped in some of these Martian rocks at the time they were expelled to space”, Explains Brigitte Zanda, a meteoritic specialist at the French Natural History Museum (MNHN).

These rare gases correspond to the “measured in the atmosphere of Mars,” recalls the researcher, co -author of the study published Friday in Nature Geosciences.

In 2012, A French meteor merchant brought him samples found in Western Sahara.

The meteorito NWA7533, nicknamed “Black Beauty”, had a “very complex” and “totally different” texture to that of other Martian meteor, she says.

The interior, dark and full of light and whitish pink grains, consisted of rocky fragments and powders that consolidated after one or several impacts on very old terrain in the southern hemisphere of Mars.

Presence of water

All Martian meteorites found so far were “related to basalts,” recalls Zanda.

These dense rocks, which form the oceanic cortex on Earth, come from rapid cooling of the Magma Ocean on the surface of a planet during its formation.

For a long time it was thought that, on Mars, the process stopped there and that the red planet did not have an equivalent to the terrestrial continents. The latter are formed by rich rocks in silica, less dense than the basalt, and that “float” on the oceanic crust.

This idea was reviewed in the last decade by the discovery, by the Robot Curiosity explorer, with more rich Martian rocks than the basaltos.

This rethinking of the first years of Mars is now confirmed by the study of Nature Geosciences.

Some of the rock fragments of “Black Beauty” turned out to be a granite, which contains a mineral composed of pure silica: quartz.

“It seems clear that they formed protocontinent in Mars and that this is related to impacts that melted a considerable thickness of the Martian cortex, and the liquids thus formed evolved towards more rich compositions in silica”Zanda suggests.

This discovery is also a clear indication of the ancient presence of water on the surface of Mars, since these phenomena are facilitated by the incorporation of water in the magma.

But since Mars is much smaller than the earth and stored less heat at the beginning, “her cortex stopped renewing very soon,” explains the researcher.

These Martian granites of 4.4 billion also shed light on the early geological evolution of our planet, since “we have no access to such old rocks on earth,” Zanda emphasizes.

The oldest rocks on our planet have been destroyed by the combined effect of erosion and plaque tectonics: those rigid plaques that move along the surface of the earth by modifying the disposition of the continents and oceans.

The only witnesses of the extremely ancient existence of the earth are zircon grains that date from 4.3 billion years ago.

But “Physical models indicate that Mars and Earth probably had very similar climatic conditions and that the geological processes that occurred in both were similar. Therefore, it is allowed to think that the processes that gave rise to the first terrestrial continents are similar to those that formed the first Martian granites”, According to the researcher.