Science. Black Beauty, the teachings of a venerable Martian

Discovered in the Moroccan desert in 2011, the meteorite, named Northwest Africa 7034 or NWA 7034, quickly became known as Black Beauty, “black beauty” in English, because its color makes it a meteorite of a kind totally unique.

Its chemical composition confirms its Martian origin: like nearly 300 of its congeners preserved in museums, it was thrown into space when an asteroid struck the red planet, and it traveled for millions of years before fall to Earth.

Zircon dated at 4.48 billion years old

But, in 2015, American researchers discovered that it was not a pebble of volcanic origin, like all those that had fallen on Earth until then, but a piece of the crust of the planet Mars. .

More specifically, Black Beauty is what specialists call an impact breccia, that is, it is an accumulation of fragments of other older rocks. And among the latter, some contain zircon dated at 4.48 billion years. The Solar System was formed 4.56 billion years ago.

With one calculation – a simple subtraction – we understand that certain rocks in Black Beauty were formed only 80 million years after the birth of the Solar System. This meteorite therefore contains the mysteries of an extremely distant past.

The “paradox of the weak young Sun”

Thus, in 2020, the analysis of Black Beauty enabled an international team, whose work was detailed in the journal “Science Advances”, to solve the “paradox of the weak young Sun”. While there is evidence that water flowed on Mars more than 3.7 billion years ago, scientists couldn’t understand how this was possible since the Sun was not shining at the time. enough to hold water in it in a liquid state.

Analysis of the chemical composition of Black Beauty revealed how the Martian atmosphere had warmed by a few tens of degrees. The very numerous impacts of asteroids have caused specific reactions on the crust, which, thanks to the release of a greenhouse gas, have made the climate warm, conducive to maintaining liquid water.

More than 90 million craters

Another discovery: last July, the journal “Nature Communications” revealed that an international team led by French researcher Anthony Lagain, from Curtin University in Australia, had managed to determine the ejection site of Black Beauty, thanks to to a crater detection algorithm. Analysis of images of the surface of Mars has identified more than 90 million of them up to 50 meters in diameter.

Then, by refining the selection criteria, the researchers managed to isolate 19 and then a single crater from which the meteorite was thrown. This is the Karratha crater, named for the occasion, located in a region corresponding to 10% of the Martian surface.

Unexplored until now, this particular zone of the Martian crust could be a site of choice for future explorations in order to better understand the processes of formation of the continental crusts of the planets.

“It does not resemble any other known rock”

How do you study a meteorite?

The meteorite is cut and the minerals are precisely observed under a scanning electron microscope. Different elements such as iron or manganese are measured in order to establish the meteorite’s chemical identity card. As for the proportion of the different forms, or isotopes, of the oxygen atom, it makes it possible to know from which planetary body the rock comes. Black Beauty is a meteorite unlike any other known Martian rock. It is also the oldest, which is why we particularly wanted to know which area of ​​Mars it came from.

Can this new method which made it possible to determine the ejection site of the Black Beauty meteorite be used for other meteorites?

Thanks to the method developed by Anthony Lagain, we now know where Black Beauty comes from. It’s as if we had picked it up. Another similar method had already made it possible to locate the origin of another type of Martian meteorite with success, which had given rise to a scientific article last year. It’s very exciting to have this possibility of retracing the history of a pebble, nevertheless bringing back samples that we would choose on the spot is always a Holy Grail. In ten years, the American space agency’s Mars Sample Return mission should make it possible to recover the samples collected by the Perseverance rover, which is currently exploring the red planet.

How does studying Black Beauty help us learn more about the formation of the earth’s crust?

The processes of crust formation are thought to be similar on all planets in our solar system. We can clearly see that the rocks that come to us from Mars are the same as on Earth, which is quite logical, since these are neighboring planets that were formed at the same time. The chemical processes are the same: the denser liquids form the cores of the planets and the less dense the mantle and the crust.

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