Starship Asterisk*

Photomicrograph of a carbon area in the NWA 7983 ureilite meteorite. Reflected light image overlain with a false-color map from Raman spectroscopy showing distribution of diamond (red) and graphite (blue). Credit: Ryan Jakubek and Cyrena Goodrich

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Scientists have offered new insights into the origin of diamonds in ureilites (a group of stony meteorites). These diamonds most likely formed by rapid shock transformation from graphite (the common low-pressure form of pure carbon) during one or more major impacts into the ureilite parent asteroid in the early solar system.

Previously, researchers have proposed that diamonds in ureilites formed like those on Earth — deep in the mantle of the planet, where the high pressures needed to form diamond (a very dense, hard form of pure carbon), are created by the weight of overlying rock. If diamonds in ureilites formed this way, then the original parent body on which they formed must have been a large protoplanet – at least the size of Mars or Mercury.

However, new research ... show there is no evidence requiring formation under the high static pressures and long growth time conditions of a planet’s deep interior. ...

• Proceedings of the NAS (online 28 Sep 2020) DOI: 10.1073/pnas.1919067117