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

Farhang Nabiei,Cécile Hébert,Jean-Alix Barrat,Teresa Dennenwaldt,James Badro,Philippe Gillet,Ahmed El Goresy,Marco Cantoni,Emad Oveisi

doi:10.1038/s41467-018-03808-6

Abstract

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.

Highlights

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
Ureilite fragments are coarse grained rocks mainly consisting of olivine and pyroxene, originating from the mantle of the ureilite parent body (UPB)[3] that has been disrupted following an impact in the first 10 Myr of the solar system[3]
We investigated the Almahata Sitta MS-170 section using transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS)

Summary

Introduction

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. The formation of such large single-crystal diamond grains along with δ15N sector zoning observed in diamond segments[7] is impossible during a dynamic event[8,9] due to its short duration (up to a few seconds10), and even more so by CVD mechanisms[11], leaving static high-pressure growth as the only possibility for the origin of the single-crystal diamonds Owing to their stability, mechanical strength and melting temperature, diamonds very often encapsulate and trap minerals and melts present in their formation environment, in the form of inclusions. The composition and mineralogy of these inclusions points to pressures in excess of 20 GPa inside the UPB, which in turn implies a planetary body ranging in size between Mercury and Mars

Methods

Results

Conclusion