'Lost planet' dropped diamonds from the sky billions of years ago

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Their first line of evidence that the space rock was a chunk of what was originally a large planetesimal came from the size of the diamonds themselves.

Specifically, the diamonds must have formed at 20 gigapascals, which is the kind of pressure found deep within a planet the size of Mars or Mercury - but the meteorites come from neither of these planets or any other planet that we know of for that matter.

The Almahata Sitta meteorite was named after where in northern Sudan the space rock exploded in 2008.

In the study, a research team found that the Almahata Sitta meteorite once belonged to a protoplanet, one of tens of early worlds that experienced impacts and buildups to ultimately create the rocky planets in our solar system. Hence this indicates that diamonds were formed at the center of a very large system that provided the required pressure and volume for diamond formation.

A chemical map shows sulfur (red) and iron (yellow) inside the inclusions in the diamond matrix. The diamonds with the Almahata Sitta meteorite formed during a transition era in the solar system, when the dust and gas that swirled around the sun coalesced into planetary embryos, then grew into planets.

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Therefore, the Almahata Sitta meteorites finally confirm the existence of large proto-planetary bodies, which had only been speculated until now.

Photo A transmission electron microscopy image of one of the diamonds recovered from the meteorite. Scientists say that under the meteorites' thick carbonized exterior hid diamonds which enclosed remnants of a long-lost planet or planetary embryo during the insane days of the early solar system. This study backs that theory and "provides convincing evidence that the ureilite parent body was one such large "lost" planet before it was destroyed by collisions some 4.5 billion years ago", the authors of the study noted.

Next, the researchers turned their attention to what are known as chemical inclusions inside the diamonds. It turned out to be a rare type of meteorite called ureilite, which has an unusual composition compared to other stony meteorites - it contains a lot of carbon in the form of nanodiamonds.

This wonderful finding could help us figure out one of the most enduring questions of astronomy, that of the formation of planets. But further evidence of sustained high pressure would be expected to be found in the minerals surrounding the diamonds, he said. They could only have formed under incredible pressure - the equivalent of diving 600 kilometers into Earth's interior or attempting to hold up 100,000 tons with your bare hands.

Many planetary and lunar scientists believe that it was a collision between Earth and a Mars-sized planet that led to the formation of our moon.