The diamonds found in stone meteorites are most likely formed by a rapid impact
Previously, researchers assumed that diamonds inureilites formed in the same way as on Earth - deep in the mantle of the planet, where the high pressure required to form a diamond (a very dense, solid form of pure carbon) is created by the weight of the overlying strata. If diamonds in ureilites appeared in the same 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 demonstrates that there is no evidence that diamonds require high pressure and time to grow deep in the depths of the planet.
The team examined diamonds in three samplesureilitis using electron microscopy, microradiography and Raman (laser) spectroscopy. Scientists have found both large (up to 100 micrometres) and small (nanometer-sized) grains of diamond, as well as metallic iron and graphite in carbon-rich regions located among the grains of silicate minerals in these samples.
The micrograph of ureilite NWA 7983 shows areas of diamond and graphite surrounded by silicate minerals Mg-Fe-Ca. Credit: Fabrizio Nestola and Oliver Christ
“We have found the largest single crystalthe diamond ever seen in ureilite, ”explains Dr. Cyrena Goodrich. “It is important to note that all of the ureilites that we examined were severely shocked based on the data obtained from their silicate minerals. This suggests that both large and small diamonds in these rocks were formed from the original graphite as a result of shock processes. "
The origin of diamonds in ureilites is importantsignificance for models of planetary formation in the early solar system. Modern asteroids, from which most meteorites originate, are very small compared to planets. However, planetary formation models predict that the planets were formed by clusters of planetary embryos (protoplanets) ranging in size from the Moon to Mars. Supporters of the high static pressure hypothesis explaining the origin of the ureilite diamonds argue that the asteroid's mother body was one of these embryos. However, scientists are demonstrating that the presence of diamonds in ureilites does not require a Mars-sized parent body.
“Our results are important because they are not onlypoint to the shock origin of diamonds in ureilites, but also refute the arguments put forward in favor of the hypothesis of a large parent body. Scientific debate and hypothesis testing are integral to the progress of science, ”concludes Dr. Goodrich.
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