Specks of diamond inside a meteor that fell from space into the Nubian Desert of northern Sudan were formed inside a long-lost planet in the early years of the solar system, according to a new scientific report.

The surprisingly large size of these extraterrestrial gemstones is the first compelling and direct evidence for the mysterious planet that has since disappeared from the solar system, either by colliding and being absorbed into another planet, or being incinerated in the sun, or cast off into outer space.

At least some of it stuck around, however, in the form of a small asteroid, perhaps four metres across, that spent millions of years in some kind of local orbit until one special night in 2008, when astronomer Richard Kowalski noticed a blip on a screen at the Mount Lemmon telescope in Arizona.

The Almahata Sitta asteroid, as it has come to be known, is special for more than just its diamonds. It was the first such object ever to be tracked from space all the way to impact on Earth.

“A few hours after Kowalski spotted it, the meteor entered the Earth’s atmosphere over the Nubian desert in northern Sudan, exploding in a massive fireball that was visible to a passing passenger jet whose pilots had been warned to watch for it. Then the search began, helpfully guided by NASA’s tracking expertise. Because it landed in a desert, this was comparatively easy, and about 10 kg of it has been recovered, in hundreds of pieces.”