Diamonds found in the Almahata Sitta meteorite originated from a lost planet from the early Solar System, according to a study published in Nature Communications this week. These findings provide evidence for the existence of large proto-planets that were the building blocks of the terrestrial planets in our solar system today.

In the early solar system it has been hypothesised that tens of Moon-to-Mars sized proto-planets formed the terrestrial planets (such as Earth and Mars) that exist today via impacts and accretion. A type of meteorite, called ureilite, is thought to be a potential remnant of these proto-planets. However, no evidence from previously examined ureilites could demonstrate that these were in fact from a proto-planet.

Farhang Nabiei and colleagues examined the Almahata Sitta ureilite meteorite, which fell to Earth in 2008 in the Nubian Desert in Sudan. The team analysed tiny crystal inclusions embedded within diamonds in the meteorite. By using transmission electron microscopy they discovered that the diamonds must have formed at pressures above 20 gigapascals. The high pressures indicate that these diamonds originally formed in a Mercury-to-Mars-sized proto-planet in the first ten million years of the early Solar System, and that these types of meteorite are the last remaining remnants of this lost planet.