An alien rock has been dug up in a limestone quarry in Sweden, where it had lain deeply buried for about 470m years. The biscuit-sized remains are unlike any other meteorite found on Earth to date, and may shed light on the history and formation of our solar system. Named Oest 65, it is thought to be a splinter of a potato-shaped rock 20-30km (12-19 miles) wide, which had smashed into another much larger body, sprinkling our adolescent planet with debris.

Previously, remnants of only one of the two rocks had been found, in the form of meteorites called chondrites. But now scientists believe they have unearthed a piece of the second space orb, boosting the theory of a major smash-up between two galactic travellers. It is thought that the breakup of the bigger chondrite body, about 100-150km across, had yielded a major cluster of rocky debris in the asteroid belt between Mars and Jupiter.

The resultant flux of extraterrestrial material, some of which rained down on Earth, coincided with a massive expansion of invertebrate ocean life at a time our planet’s landmass was largely fused together into a supercontinent called Gondwana. Along with about 100 chondrite pieces discovered to date, the new alien fragment had sunk to the floor of an ocean covering parts of what today is a limestone quarry in southern Sweden.

The team measured telltale signs of cosmic radiation in the meteorite to determine how long it had flown around in space before crashing to Earth. The extraterrestrial lander may be the first documented example of an “extinct meteorite”, so called because its parent body had been entirely consumed by space collisions, meaning no more fragments can fall to Earth today. Chondrites still drop to our planet every now and then. The findings mean that today’s meteorites – on which scientists base much of their assumptions about our solar system’s formation – are not fully representative of what is, and once was, out there.