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Source of oldest, rarest meteorite found

Artist's impression of a giant meteor.
Artist's impression of a giant meteor.  


By Richard Stenger
CNN

(CNN) -- A mysterious space rock that defies conventional classification contains material that predates the solar system, and likely came from the outer edge of the asteroid belt, scientists said Thursday.

The alien boulder stunned onlookers last year when it streaked over Canada, exploded into a giant fireball and slammed into a frozen lake in the Yukon.

The landing site helped keep preserve the fragile remnants of the space rock, including frozen volatile gases that otherwise might have evaporated.

"This meteorite turned out to be the most primitive meteorite we know," said Brown University planetary geologist Takahiro Hiroi, lead author of a report in the August 24 edition of the journal Science.

The Tagish Lake meteorite resembles space rocks known as carbonaceous chondrites, but contains much more carbon and pre-solar grains, which predate the solar system.

"It contains more pre-solar grains than any other meteorites," Hiroi said.

Pre-solar grains, which predate the birth of the solar system 4.6 billion years ago, were produced in the fiery death of an ancient star. The explosion provided the raw materials for our sun and planets, according to scientists.

Most of the building blocks of our solar system vaporized and reformed, but pre-solar grains never melted.

A 250-ton space boulder left this smoky trail over British Columbia in January 2000.
A 250-ton space boulder left this smoky trail over British Columbia in January 2000.  

The Tagish Lake rock fragments match nothing found on Earth. But Hiroi and colleagues at Brown and NASA analyzed their chemical fingerprint and determined that the meteorite came from a particular class of space boulders, the oldest known, in the asteroid belt between Mars and Jupiter.

Hiroi is hardly surprised that such meteorites have not been recovered before. Few of the D-type asteroids reside in areas where space rocks collide and produce fragments that might drift to Earth. And the rare D-type meteorites that reach our atmosphere likely burn up completely because they are so fragile.

"This particular meteorite was so big and had a soft landing on ice and snow. That may be why it survived," he said.

On January 18, 2000, the 250-ton Tagish Lake monster stunned British Columbia onlookers when it ignited into a giant fireball and produced the explosive equivalent of 5 to 10 tons of TNT, according to Purdue University researchers.






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RELATED SITES:
• Brown University
• NASA Home Page
• Science Magazine Home

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