mardi 17 avril 2018

Diamonds tell a vanished planet

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April 17, 2018

EPFL scientists have examined a slice of a meteorite containing diamonds formed under high pressure.

Image above: The fragment in question could be studied. Image Credits: EPFL/Hillary Sanctuary.

The study of EPFL researchers shows that the body of origin was a planetary embryo of a size between that of Mercury and that of Mars. On October 7, 2008, an asteroid a little over four meters in diameter entered the Earth's atmosphere and exploded 37 kilometers above the Nubian Desert in Sudan. During his explosion, he threw multiple fragments on the surface of the desert.

Only fifty fragments, of a size of 1 to 10 centimeters, were collected, for a total mass of 4.5 kilos. It is mainly ureilites, a rare type of stony meteorite that often contains small clusters of nanometer-sized diamonds, said Tuesday the Federal Institute of Technology Lausanne (EPFL) in a statement.

The prevailing view is that these tiny diamonds can form in three ways: shock waves of enormous pressure from high-energy collisions between the original meteorite and other objects in space, a deposition by chemical vapors or the "normal" static pressure inside the original body, as for most diamonds on Earth.

Planet Embryo

EPFL scientists, along with colleagues in France and Germany, studied diamonds with a diameter of 100 microns in some of these meteorites. The analysis showed that the diamonds contained chromite, phosphate and iron-nickel sulphides, which scientists call "inclusions".

It has long been known that they exist in terrestrial diamonds, but they are described for the first time in an extraterrestrial body. The particular composition and morphology of these materials can only be explained if the pressure under which the diamonds were formed was greater than 20 GPa (giga-pascals).

Image above: Artist’s conception of the dust and gas surrounding a newly formed planetary system. Image Credit: NASA.

And this level of internal pressure can be explained only if the body of origin was a planetary "embryo" of a size between those of Mercury and Mars, according to the layer in which the diamonds were formed.

Lost planets

Many models have predicted that these planetary embryos existed during the first million years of our Solar System, and the study provides irrefutable proof of their existence. Many planetary embryos had the size of Mars, like the one that struck the Earth to give birth to the Moon.

According to the authors, "this study provides compelling evidence that the original body of this meteorite was one of those 'lost' great planets destroyed by collisions 4.5 billion years ago." . The discovery is published in Nature Communications.

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Images (mentioned), Text, Credits: ATS/ Aerospace/Roland Berga.

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