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Violent Solar System History Uncovered by WA Meteorite

Curtin University scientists have shed some light on the bombardment history of our solar system by studying a unique volcanic meteorite recovered in Western Australia.

Captured on camera 7 years ago falling on the Nullarbor Plain, the Bunburra Rockhole Meteorite has unique characteristics that suggest it came from a large asteroid that has never before been identified.

A/Prof Fred Jourdan says the meteorite is evidence for a series of asteroid collisions more than 3.4 billion years ago. “Nearly all meteorites we locate come from Vesta, the second largest asteroid in the solar system. But after studying the meteorite’s composition and orbit, it appears it derived from a large unidentified asteroid that was split apart during the collisions.”

When Jourdan and colleagues dated the meteorite they found evidence for three impact events between 3.6 billion and 3.4 billion years ago. “These ages are pretty old by terrestrial standards, but quite young for a meteorite since most are dated at 4.57 billion years old, when the solar system began,” Jourdan said.

“Interestingly, the results also showed that not a single impact occurred on this meteorite after 3.4 billion years ago until it fell to Earth in 2007. The same impact history has also been observed from meteorites originating from Vesta, with any impact activity stopping after 3.4 billion years ago. Obtaining similar information from two large yet distinct asteroids is an exciting discovery as it confirms some of the bombardment history of our solar system.”

Jourdan said the impacts may have stopped 3.4 billion years ago because the asteroids were too small to be a target for collisions or were protected by regolith, a thick blanket of cushiony powder usually found at the surface of asteroids.

The research has been published in Geochimica and Cosmochimica Acta.