A giant planetary embryo revealed by inclusions in meteorite diamonds

According to current scientific models, the telluric planets in our solar system formed by accretion, following giant energetic impacts of dozens of planetary embryos, between the size of Mercury and Mars. However, traces of these large proto-planets had not yet been found.

Researchers at the Ecole Polytechnique Fédérale de Lausanne (EPFL), in partnership with the Institut de Physique du Globe de Paris (IPGP), the Bavarian Research Institute of Experimental Geochemistry and Geophysics (BGI – University of Bayreuth) and the Institut Universitaire Européen de la Mer (IUEM – University of Western Brittany), have studied diamond samples found in a meteorite that exploded in the Earth’s atmosphere over the Nubian Desert in Sudan in 2008. This Almahata Sitta meteorite (named after the collection of fragments found) is a ureilite, one of the main families of achondritic meteorites whose parent body underwent major impacts during the first ten million years of the solar system. Transmission electron microscopy of these diamonds has revealed inclusions of chromite, phosphate and above all iron and nickel sulphides, whose composition and morphology can only be explained by a formation pressure of over 20 GPa. This level of internal pressure implies that the original body was a planetary embryo of a size between those of Mercury and Mars, providing evidence for the existence of ancient planetary bodies destroyed by accretion.