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Updated: Fri, 21 Mar 2014 16:11:25 GMT | By CBC News, cbc.ca

Meteorite from Ontario fireball described as 'Rosetta stone'

Composite all-sky camera image of fireball as seen from Aylmer, Ontario. Western University, the Physics and Astronomy Department

Composite all-sky camera image of fireball as seen from Aylmer, Ontario. Western University, the Physics and Astronomy Department

Canadian and NASA researchers believe one or more fragments of a rare and valuable meteorite may have landed near St. Thomas, Ont., after a fireball streaked across the sky in southern Ontario Tuesday night.

"This is very exciting for us," said Western University meteor physicist Peter Brown at a news conference Friday, where he appealed to the public for help in finding the meteorite fragment or fragments.

Meteors are fragments of asteroids or comets that fall through the Earth's atmosphere, where they burn up, producing a bright light. Fireballs are meteors that appear brighter than the planet Venus, and are typically from larger space rocks.

Tuesday night's fireball first appeared in the sky at 10:45 p.m. about 75 kilometres above Port Dover, Ont., and headed almost due west before vanishing at an altitude of 32 kilometres between Aylmer and St. Thomas. It was widely seen in Toronto, Hamilton, London and other parts of southern Ontario, where skies were clear.

Golf ball- or baseball-sized fragments

Brown, director of Western's Centre for Planetary Science and Exploration, estimated the space rock was originally the size of a basketball. His colleague, Western University meteorite curator Phil McCausland, said one or more fragments "about the size of a golf ball or baseball" likely landed about five kilometres north or northwest of St. Thomas.

The meteorite from this event is particularly rare and valuable to science because the fireball was captured by seven all-sky cameras of Western's Southern Ontario Meteor Network, allowing researchers to calculate its orbit – something that has only been possible for about 20 other meteorites in the past.

"Each one of those is like a Rosetta stone," Brown said, referring to a famous Egyptian artifact that was a key to deciphering ancient Egyptian hieroglyphics.

Unusual orbit

Not only was there good data on the space rock's orbit, but that orbit itself was special. It turns out the rock has spent most of its recent past circling closer to the sun than the Earth, having left its original orbit in the asteroid belt between Mars and Jupiter long ago.

Bill Cooke, head of NASA's meteoroid environment office, said only one other meteorite known to have come from that kind of orbit has ever been recorded.

"This is not your run-of-the-mill meteor fall," he said at the news conference. "This is a very unusual orbit. We're really interested in knowing what type of object was in this … We won't know that until we find a piece of it."

Brown said the meteorite is a piece of the early solar system.

"This is like a poor man's space probe. It comes to us," he said. "It's going to tell us … what made the Earth, what made the other planets."

Brown is asking for the public to help look for the meteorite – described as a rock that looks like it was painted black – and contact the researchers if they find it.

The researchers are also interested in hearing accounts from anyone who may have heard a whistling sound "like artillery coming in" or a thud after witnessing the fireball, indicating that it may have landed within a few hundred metres. That may help narrow down the area for the search.

Brown noted that it's the first time in five years that such a meteor fall has taken place in southern Ontario. The last time researchers issued a callout like this, the meteorite was recovered days later by a member of the public near Grimsby, Ont., where it had crashed through the windshield of an SUV.

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