Aug 08, 2014 |
Violent solar system history uncovered by Australian meteorite
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(Nanowerk News) Captured on camera seven years ago falling on the WA side of the Nullarbor Plain, the Bunburra Rockhole Meterorite has unique characteristics that suggest it came from a large asteroid that has never before been identified.
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Associate Professor Fred Jourdan, along with colleagues Professor Phil Bland and Dr Gretchen Benedix from Curtin’s Department of Applied Geology, believe the meteorite is evidence that a series of collisions of asteroids occurred more than 3.4 billion years ago ("40Ar/39Ar impact ages and time–temperature argon diffusion history of the Bunburra Rockhole anomalous basaltic achondrite").
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“This meteorite is definitely one-of-a-kind,” Dr Jourdan said.
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“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.”
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The research team dated the meteorite with the argon-argon technique, a well-known method for dating impact crater events, to offer a glimpse of the asteroid’s impact history.
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They obtained three series of ages indicating that the meteorite recorded three impact events between 3.6 billion and 3.4 billion years ago.
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“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,” Dr Jourdan said.
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“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.
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“The same impact history has also been observed from meteorites originating from Vesta with any impact activity stopping after 3.4 billion years ago.
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“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.”
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Dr Jourdan said the reason for impacts stopping after 3.4 billion years ago could have been from the asteroids being too small in size to be a target for collisions, or protected by regolith, a thick blanket of cushiony powder usually found at the surface of asteroids.
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