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Current Affairs

Origin of diamonds in meteorites

Date: 30 September 2020 Tags: Miscellaneous

Issue

Scientists have offered new insights into the origin of diamonds in a group of stony meteorites called ureilites.

 

Background

These diamonds most likely formed by rapid shock transformation from graphite during one or more major impacts into the ureilite parent asteroid in the early solar system.

 

Details

  • 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 a diamond, are created by the weight of the 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.

  • The team investigated diamonds in three ureilite samples using electron microscopy, micro X-ray diffraction, and Raman laser spectroscopy.

  • Their investigations revealed both large and small grains of diamond, along with metallic iron and graphite, in the carbon-rich regions located among the silicate mineral grains in these samples.

  • The origin of diamonds in ureilites has important implications for models of planetary formation in the early solar system.

  • Present day asteroids, from which most meteorites originate, are very small compared to the planets.

  • However, planetary formation models predict that planets formed as a result of the accumulation of Moon- to Mars-sized planetary embryos (protoplanets).

  • Previously it was thought that micrometer-sized diamonds were too large to have formed in the short time periods during which peak pressures are maintained in impact events.

  • However, researchers calculated that peak shock pressures could last for 4-5 seconds during a major impact such as that inferred for the ureilite parent body.

  • This is sufficient for the formation of 100 micrometer-sized diamonds when catalyzed by the presence of metal, a process commonly used in the production of diamonds in the industry.