"People described it as coming over the mountains, over their heads, and then disappearing over the horizon," says Dr. Peter Brown of the University of Western Ontario. "It was very long-lasting and unusual. We estimate that this object was about 7 meters across and 200 to 250 metric tons. This wasn't your average meteoroid -- it was basically a C-class asteroid detonating in the atmosphere over the Arctic!"
Above: Duane Hilton's rendition of a brilliant fireball streaking above a snowy Canadian landscape.
The first fragments of the object were discovered in January by a local resident near the spot where the meteorite hit.
Above: This sequence of pictures was captured by Ewald Lemke (Atlin Realty, Atlin, British Columbia) on January 18, 2000. It shows the expanding smoke train of the Yukon meteor over a 14-minute period. The first frame shows a smoky red vapor trail just 1 minute and 30 seconds after the initial flash.
In April, 2000, Brown and a team of scientists returned to the icy lake to look for more fragments that might have been uncovered as the snow began to melt with the coming of Spring.
C-class asteroid --these comprise about 75% of all objects in the asteroid belt. They are extremely dark and have chemical compositions similar to the Sun, minus hydrogen and helium (see also S-type and M-type asteroids).
carbonaceous chondrite -- a dark, crumbly carbon-rich meteorite, similar in appearance to a charcoal briquette.
"The outer layers were hot [due to friction with the atmosphere], but carbonaceous chondrites are very porous and don't conduct heat very well," he explained. The inside of the object was still frozen by the icy cold of space when the pieces reached the ground.
These are the only freshly fallen meteorite fragments ever recovered and transferred to a laboratory without thawing. Keeping the fragments continuously frozen minimized the potential loss of organic materials and other volatile compounds in the fragments.
"This is the first carbonaceous chondrite found just after landfall since the Murchison meteorite in 1969. This will be the first time ever that we can use modern techniques to study one of these. People are going to want to look for fullerenes and amino acids. This meteorite was 6% carbon, by weight; other carbonaceous chondrites are only 2%. It's very rich in carbon compounds."
Carbonaceous chondrites, which comprise only about 2 percent of meteorites known to have fallen to Earth, are typically difficult to recover because they easily break down during entry into Earth's atmosphere and during weathering on the ground.
"They are rare because they are so very fragile," continued Brown. "You need an incoming meteorite that's huge -- something that can afford to lose hundreds of metric tons as it blazes through the atmosphere and still deposit many kilograms on the ground."
The fragments -- lumps of crumbly rock with scorched, pitted surfaces -- resembled partly used charcoal briquettes: black, porous, fairly light -- about the same density as lightweight pumice.
Brown and colleagues are trying to compute an accurate orbit for the meteorite to discover where it came from.
Although the Yukon meteor was spectacular, Brown notes that it didn't add much to the amount of extraterrestrial material that falls to Earth every day.
"Daily the Earth is bombarded by 80 to 100 metric tons of microscopic space dust (in the form of 10-5 gm particles)," said Brown. "Thus, the Yukon meteorite was only 2 or 3 days worth of space dust."
Editor's note: The Nomenclature Committee of the Meteoritical Society has officially designated the name Tagish Lake Meteorite for the Yukon fall specimens.
Yukon Meteor Blast -January 25, 2000, Space Science News
Huge Fireball Dazzles Midwest -Thousands of people across the Eastern US saw a brilliant fireball streak across the night sky just 24 hours before the 1999 Leonids. (November 17, 1999)
Frequently Asked Questions about Fireballs -from the American Meteor Society
YUKON METEORITE MAY PROVIDE “NEW WINDOW INTO THE UNIVERSE” -- Johnson Space Center press release H00-41.