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Rare meteorite points to volcanism in early solar system

Solar system evolution Volcanic activity was present on small asteroids in the first few million years after the solar system's birth, according to a new study.

The results, reported in the journal PNAS, are based on an analysis of one of the most unique meteorites ever found.

"We found rocks were being produced by volcanism on small asteroids just six-and-a-half million years after the formation of the first solid material in the solar system," says Professor Addi Bischoffa of the University of Munster in Germany.

"I would have thought that these kinds of rocks could only have formed much later, on larger bodies like Earth.

"But to have this happening on asteroids so early is fantastic."

Bischoffa and colleagues examined samples of the Almahata Sitta meteorite, found in Sudan in 2008.

Using optical and electron microscopy, Bischoffa and colleagues found the meteorite contained silica-rich minerals that can only be produced by rapidly crystallised volcanic rock.

"Rapid crystallisation can be caused by an explosion or when lavas come out of the Earth and experience rapid cooling, and this must have happened on the parent body of this meteorite," says Bischoffa.

Formed from a unique asteroid

The Almahata Sitta meteorite is a collection of 600 samples that originated from asteroid 2008 TC3, which was the first asteroid to be tracked in space before it exploded above the Nubian Desert.

It belongs to a rare class of meteorites known as ureiltes, which contain a mixture of minerals usually found on a variety of different asteroids.

"Almahata Sitta is like the whole meteorite classification system in the one meteorite," says Bischoffa.

"It was a very strange meteorite and this tells us something about how these asteroids formed and reformed in the early solar system."

The early solar system was a violent place with rocks and asteroids constantly crashing into each other.

Depending of the speed of these impacts, the asteroids would either meld together to form larger asteroids, or be smashed to pieces.

According to Bischoffa, the original parent bodies of the Almahata Sitta meteorite were destroyed in collisions with other asteroids about six-and-a-half million years after the solar system's first solids condensed out of the solar nebula.

The authors believe at least one of these collisions occurred while the asteroid was still partly molten, between 1200 and 1300°C.

The debris left over from the collisions later reformed into a new asteroid in another part of the solar system. This new asteroid was the parent body for the Almahata Sitta meteorite.

"There must have been lots of destruction of parent bodies with the debris moving to different parts of the solar system where they formed a new parent body," says Bischoffa.

"Some of these are completely different rocks, the mixture of different minerals in the one meteorite is fantastic.

"We finally found a piece with all the characteristics people have been looking for."