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In Depth: Tracking Rogue Rocks From Outer Space

 Ancient Space Rock Holds New Clues

Philip Downey,
Discovery.com News

Oct. 12, 2000 — A meteorite that plummeted to Earth in northern Canada earlier this year may be the most primitive and pristine fragment of the solar system scientists have ever examined.
Researchers say it should aid them in determining the composition of our solar system in its earliest days.
 

Meteorite Fragment

The meteorite landed in the far north of Canada on the icy surface of Tagish Lake, providing the scientists with a dash of serendipity — the cold temperature may have better preserved gases and structures inside the rock fragments and also stopped the bits from sinking to the lake bottom.

The first man on the scene, Jim Brooks, bagged and froze the pieces he found to reduce contamination from the surrounding environment.

"It's a rare kind of meteorite," said Peter Brown, the University of Western Ontario astronomer who led the analysis. The meteorite belongs to a class known as carbonaceous chondrites, which compose only 2 percent of the meteorites in our solar system. Even so, "It doesn't fit the categories of previous carbonaceous chondrites."

He and a team of astronomers and mineralogists, reported their findings in this week's issue of Science.

Brown his colleagues believe their meteorite is more primitive than the other carbonaceous chondrites, based on an analysis of the different elements it contains, and the mineral structures found within.

"It may be much less altered than other chondrites, which would be very exciting," said Jeff Grossmann, of the U.S. Geological Survey.

Carbonaceous chondrites, generally deemed to be the most primitive of all asteroids, have had their mineral structures changed by water and heat. Further analysis of these grains may reveal the original chemical buildings blocks of our solar system, and by extension, life on Earth.

The meteorite came down on Jan. 18. The heat generated by its impact with the atmosphere was the largest ever recorded by satellites. It was also photographed, videotaped and seen by many people living in the province of Alberta before it exploded and crashed to the ground, spraying pieces over the surface of Tagish Lake and nearby forests in the Yukon territory.

With all these records of the meteorite's path, "it's the first recovered meteorite for which an accurate orbit exists," said Brown.

The biggest of the 500 meteor fragments weighs about half a pound. The complete meteorite probably weighed around 200 metric tons, "or about twice as much as the space shuttle," said Brown.