Solar system history falls from the heavens

By Stefanie Achkewich

Fire in the sky. Such was the scene witnessed by residents of northern British Columbia and the Yukon the evening of Jan. 18, 2000. At approximately 8:43 p.m., a meteorite blazed through the heavens and found a final resting place in the ice of Taku Arm in Tagish Lake.

"This may be the crown jewel of meteorite finds," said Peter Brown, a professor of physics and astronomy at the University of Western Ontario. "This discovery will aid scientists in the reconstruction of the early solar system."

Brown, working alongside Alan Hildebrand, a professor in the Department of Geology and Geophysics at the University of Calgary, are the lead authors of the report featured on the cover of the Oct. 13, 2000 issue of the international journal Science.

"The standard composition of the solar system is partly defined by the most primitive meteorite in existence," explained Dr. Neil McRae, an earth sciences professor at Western and a co-author on the Science paper. "If our results are proven correct, this new discovery will ultimately change that definition."

As the largest meteorite fall in Canadian history, it has attracted research teams from around the world including the U of C, UWO, the United States and the United Kingdom.

"There are things to learn we don’t expect," says Hildebrand. "For example, we may learn about nebular chemistry. We may learn things we don’t fully appreciate."

Jim Brook, a resident of the Tagish Lake area, was the first person to retrieve pieces from the crash site. Recovery of the meteorite involved the work of 11 people over a period of 18 days. To date, 500 fragments have been found while over a tonne of ice containing fragments is in storage for future study.

Tagish Lake Meteorite–named after the town it was discovered near–is a new type of carbonaceous chondrite, a rare, organically rich, charcoal-like class of meteorites. Carbonaceous chondrite meteorites make up about three percent of meteorite finds in the world. The chemical class most closely resembling this meteorite constitutes less than 0.1 per cent of all meteorites recovered to date. The Science report suggests the Tagish Lake Meteorite to be even more primitive and therefore may represent a new class.

Hildebrand emphasized the great fortune of the Tagish Lake Meteorite as he explains the nature and fate of a meteorite as it passes through the atmosphere.

"[Tagish Lake] is extremely porous and not well cemented. The average [meteorite] density is 2.7, Tagish Lake has a density of 1.5. From a 200 tonne meteorite less than one 1/1000 made it to the ground."

"The most significant and exciting things to be discovered in this meteorite may not yet be known," added Hildebrand. "We, together with Jim Brook, are supplying material to dozens of researchers located around the world for their studies. It is a delightful and somewhat rare situation for scientists when we can’t predict what may be learned."

Hildebrand is very optimistic because of the possibilities the meteorite opens to the U of C.

"The [U of C] has set a policy of getting involved in planetary science," says Hildebrand. "Such early success is very encouraging. We need to study whole solar systems not just the planet. Students can now pursue studies oriented in this direction."

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