A large planetary body inferred from diamond inclusions in a ureilite meteorite

Farhang Nabiei (1) , James Badro (1, 2) , Teresa Dennenwaldt (1) , Emad Oveisi (1) , Marco Cantoni (1) , Cécile Hébert (1) , Ahmed El Goresy (3) , Jean-Alix J-A Barrat (4) , Philippe Gillet (1)

1 EPFL - Ecole Polytechnique Fédérale de Lausanne
2 IPGP - Institut de Physique du Globe de Paris
3 BGI - Bayerisches Geoinstitut
4 IUEM - Institut Universitaire Européen de la Mer

Planetary formation models show that terrestrial planets are formed by the accretion of tens of Moon-to Mars-sized planetary embryos through energetic giant impacts. However, relics of these large proto-planets are yet to be found. Ureilites are one of the main families of achondritic meteorites and their parent body is believed to have been catastrophically disrupted by an impact during the first 10 million years of the solar system. Here we studied a section of the Almahata Sitta ureilite using transmission electron microscopy, where large diamonds were formed at high pressure inside the parent body. We discovered chromite, phosphate, and (Fe,Ni)-sulfide inclusions embedded in diamond. The composition and morphology of the inclusions can only be explained if the formation pressure was higher than 20 GPa. Such pressures suggest that the ureilite parent body was a Mercury-to Mars-sized planetary embryo.

Domaines: Planétologie et astrophysique de la terre [astro-ph.EP]

Farhang Nabiei, James Badro, Teresa Dennenwaldt, Emad Oveisi, Marco Cantoni, et al.. A large planetary body inferred from diamond inclusions in a ureilite meteorite. Nature Communications, 2018, 9, pp.1327. ⟨10.1038/s41467-018-03808-6⟩. ⟨insu-02135380⟩