Scientists have proposed a new understanding of the origin of diamonds in ureilites, which belong to the group of stony meteorites. The results of the study, led by Prof. Fabrizio Nestola and Dr. Kirena Goodrich, are published in the journal Proceedings of the National Academy of Sciences. The Association for Space Research of Universities reports.
The diamonds found in stony meteorites most likely formed as a result of the rapid impact transformation of graphite during one or more major collisions with the parent asteroid ureilite in the early solar system.
Previously, researchers suggested that diamonds in ureilites formed in the same way as on Earth – deep in the planet’s mantle, 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 samples of ureilite using electron microscopy, X-ray microscopy, 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.
We have discovered the largest single-crystal diamond ever observed 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 important 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 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 not only point to the shock origin of diamonds in ureilites, but they also refute the arguments advanced in favor of the large parent body hypothesis. Scientific debate and hypothesis testing are integral to the progress of science, ”concludes Dr. Goodrich.