It Came from Outer Space

A decade ago today, a rock that probably contains the stardust that created our Sun landed on a quiet lake in the Yukon

Over 60 miles long, a little over a mile wide and situated in a pristine wilderness of vast spruce forests in Canada's sub-arctic Yukon territory, Tagish Lake endures long, dry winters. Lake trout, jackfish and arctic grayling ply its chilly waters.

But this placidity was broken at 4:43 PM on January 18, 2000, when a massive fireball streaked across the sky and crashed into Tagish's frozen surface.

It was a meteoroid, a piece of cosmic debris.

Meteoroids range in size anywhere from a tiny speck of dust to a massive boulder. The one that exploded in the upper atmosphere on that particular Tuesday a decade ago -- somewhere between 20 and 30 miles above the surface of the Earth -- was a big one.

The Tagish Lake meteoroid is estimated to have been about 13 feet in diameter and weighed about 56 tons before it entered our atmosphere.

The explosion created 1.7 kilotons of energy -- about a tenth as powerful as the atomic bomb that was dropped on Hiroshima. Though 97% of it vaporized during entry, the meteoroid produced countless fragments, about 500 of which have been recovered.

The resulting Tagish Lake meteorites (those remnants of the meteoroid that survived the fiery entry into the Earth's atmosphere), are carbonaceous chondrites, a rare group of meteorites that represent less than 5% of all known meteorite falls and include the most primitive ones ever found.

The Tagish Lake meteoroid was most likely a piece of 773 Irmintraud, a D-type asteroid or "minor planet" that orbits the Sun between the orbital paths of Jupiter and Mars.

It contains primitive and unchanged stellar dust that most likely was a part of the stellar cloud that created our Sun and solar system.

A 2006 NASA study of globules from the meteorite found that they "resemble cometary carbon, hydrogen, oxygen, and nitrogen (CHON) particles, suggesting that such grains were important constituents of the solar system starting materials."

Tagish Lake is famous for being a part of the Alaska-Yukon corridor that gave passage to some 40,000 frenzied fortune hunters on their way to the gold fields near Dawson City during the Klondike Gold Rush of 1897.

While the Tagish Lake meteorite wouldn't fetch a dime for a gold trader, it might fare well on the diamond market: It has more nanodiamonds than any other meteorite ever found.

But its real value is its ability to give us a look into the birth of our particular corner of the universe.

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image: a piece of the Tagish Lake meteorite, recovered from the ice in British Columbia (credit: Mike Zolensky, NASA JSC)