Meteorite violent origins
August 9, 2014

Violent History Of Bunburra Rockhole Meteorite

April Flowers for - Your Universe Online

Seven years ago, the Bunburra Rockhole Meteorite fell on the Western Australia (WA) side of Nullarbor Plain and was captured on camera. A new study, published in Geochimica and Cosmochimica Acta, indicates that the unique characteristics of the meteorite suggest it originates from a never-before-identified asteroid.

The research team — comprised of Curtain University's Associate Professor Fred Jourdan, Professor Phil Bland and Dr. Gretchen Benedix, all from the Department of Applied Geology - believe the meteorite carries evidence of a series of asteroid collisions that took place more than 3.4 billion years ago.

"This meteorite is definitely one-of-a-kind,” Dr Jourdan said.

“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.”

To gain a glimpse into the history of the meteorite, the team used argon-argon dating, a well-known method for dating impact crater events. Three series of ages were obtained with this method, indicating the meteorite recorded three impact events which happened 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,” Dr 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.”

The reason the impacts probably stopped 3.4 billion years ago, according to Jourdan, might be because the asteroid was too small in size to be a target for collisions, or it could have been protected by regolith — a thick blanket of cushiony powder usually found at the surface of asteroids.

According to the Western Australia Museum, the Bunburra Rockhole meteorite was an extraordinary find in many ways. The meteorite's fall was the first to ever be solely predicted on data from dedicated instruments. It is the first meteorite known to be from a near-Earth, or Aten-type, orbit.

It is also the first instrumentally observed meteorite fall in the Southern Hemisphere. The fall was captured on July 20, 2007, by two of the four cameras in the Autonomous All-Sky Desert Fireball Camera Network. These satellite monitored cameras are designed to calculate the orbits of the fireballs, and determine the meteorite fall position for later recovery.

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