Western researchers help recover meteorites

By Chantall Van Raay
June 01, 2000

 
Meteor scientist Peter Brown and his research team at the Tagish Lake site in northwestern British Columbia where hundreds of meteor fragments have been discovered. Left to right: UWO earth sciences grad students Rob Carpenter and Philip McCausland; Brown, Department of Physics and Astronomy; earth sciences grad student Heather Gingerich and Jim Brook, the person who discovered the meteorites.
 
Hundreds of fragments called 'the find of a lifetime'
Western, with the University of Calgary and NASA, announced the recovery of the largest meteorite fall in Canadian history yesterday.

Mother Nature played a big part in the recovery of the carbonaceous chondrite, a rare, organically rich, charcoal-like class of meteorite that crashed in northwestern British Columbia earlier this year. More than 500 fragments of the meteor have been located, with 410 of these documented and more than 200 physically recovered, says Peter Brown, meteor scientist in Western's Department of Physics and Astronomy and co-leader of the meteorite recovery investigation.

Finding the meteor fragments might not have been possible if it weren't for a number of favorable circumstances, says Brown. Several hundred thousand fragments fell, but because the material breaks up easily, matter that fell on land likely crumbled, making it unrecoverable. A significant amount of the meteor fell on the frozen lake, however, and the highly volatile material was consequently encased in ice, explains Brown.

Another benefit was that on April 20, the meteor fragments were discovered by amateur astronomer Jim Brook, who took great care in collecting the black space rocks so as not to contaminate them. Brook's careful collection of the pristine meteorites is said to have opened brand new doors for meteorite researchers around the world. The find will assist planetary scientists around the world, including earth scientists at Western. "It will provide a whole host of insight into early chemistry in the solar system," Brown says.

The meteor fell to earth on the morning of Jan. 18 on the ice of Taku Arm in Tagish Lake, a remote area between Atlin, B.C. and Carcross, Yukon Territory. The lake has subsequently been designated the Tagish Lake Meteorite. Thousands of eye-witnesses and satellite data collected by the United States Department of Defense, made it possible to estimate the meteor fell at a velocity of 15- to 16-kilometres per second, from the mid- to outer-asteroid belt.

Brown and Alan Hildebrand, planetary scientist in the Department of Geology and Geophysics at the University of Calgary, collaborated over the phone about the meteor, coordinating the acquisition of the find and co-investing in the project. "This is certainly the find of a lifetime," says Brown. "The size of the initial object, the extreme rarity and organic-richness of the meteorites combined with the number we have uncovered makes this a truly unique event," he says, noting it is also some of the lightest rock that has ever been found.

"There have only been four previous meteorites for which accurate orbits are known and no orbits for a carbonaceous chondrite have ever been secured," he says. "The entire process of recovery of the material and determination of where it comes from makes this the scientific equivalent of an actual sample-return space mission - at a thousandth of the cost."

It represents only three per cent of all meteors which fall to earth, says Brown, adding the last two carbonaceous chondrite meteors of its class fell almost concurrently 30 years ago, one in Mexico and one in Australia.

"This is the largest documented fireball that has occurred over land and the largest object to hit the earth in the last two to three years," says Brown. The energy of the approximate 200-metric tonne fireball, which measured about six meters in diameter, was roughly half the energy of the atomic explosion over Hiroshima, Brown described. Only five C1 carbonaceous chondrite meteorites have ever been recovered.























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