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Tagish Lake
A 159 gram fragment of the Tagish Lake meteorite
Type	Chondrite
Class	Carbonaceous chondrite
Group	C2 ungrouped
Shock stage	S1
Country	Canada
Region	British Columbia
Coordinates	59°42′16″N 134°12′5″W / 59.70444°N 134.20139°W / 59.70444; -134.20139Coordinates: 59°42′16″N 134°12′5″W / 59.70444°N 134.20139°W / 59.70444; -134.20139[1]
Observed fall	Yes
Fall date	January 18, 2000 08:43:42 pst
Total Known Weight	10 kg

The Tagish Lake meteorite fell at 16:43 p.m. on 18 January 2000 in the Tagish Lake area in Yukon, Canada.

History

Tagish Lake in the Yukon, the impact site of the "Tagish Lake" meteorite

Fragments of the Tagish Lake^[1] meteorite impacted upon the Earth on January 18, 2000 at 16:43 UT after a large meteoroid exploded in the upper atmosphere at an estimated altitude of 30 to 50 km with an estimated total energy release of about 1.7 kilotons. Following the reported sighting of a fireball in the Tagish Lake area in the Yukon Territory and northern British Columbia, Canada, more than 500 fragments of the meteorite were collected from the lake's frozen surface. Post-event atmospheric photographs of the trail left by the associated fireball and U.S. Department of Defense satellite information yielded the meteor trajectory ^[2]. Most of the stony, carbonaceous fragments landed on the Taku Arm of the lake, becoming encased in ice after landing on the lake's frozen surface. The passage of the fireball and the high-altitude explosion set off a wide array of satellite sensors as well as seismographs.

Meteoroid

The Tagish Lake meteoroid is estimated to have been 4 metres in diameter and 56 tonnes in weight before it entered the Earth's atmosphere. However, it is estimated that only 1.3 tonnes remained after ablation in the upper atmosphere and several fragmentation events, meaning that around 97% of the meteorite had vaporised. Of these 1.3 tonnes of fragmented rock, only 0.1% was found and collected.

Specimens

Tagish Lake is classified as a carbonaceous chondrite, type C2 ungrouped. The pieces of the Tagish Lake meteorite are dark grey to almost black in color with small light-colored inclusions, and a maximum size of ~2.3 kg.^[2] Except for a greyish fusion crust, the meteorites have the visual appearance of a charcoal briquette.^[3] The fragments were transported in their frozen state to research facilities after they were pried or sawn from the lake's icy top layer. They were collected by researchers from the University of Calgary and University of Western Ontario and were studied in collaboration with researchers from NASA. The meteorite is currently held in the collection at the Royal Ontario Museum and the University of Alberta.

Analysis and classification

Analyses have shown that Tagish Lake fragments are of a primitive age, containing unchanged stellar dust granules that may have been part of the cloud of material that created our solar system and Sun. This meteorite shows some similarities to the two most primitive carbonaceous chondrite types, the CI and CM chondrites; it is nevertheless quite distinct from either of them. Tagish Lake has a much lower density than any other type of chondrite and is actually composed of two somewhat different rock types. The major difference between the two lithologies is in the abundance of carbonate minerals; one is poor in carbonates and the other is rich in them.^[4]

A portion of the carbon in the Tagish Lake meteorite is contained in what are called nanodiamonds -- very tiny diamond grains at most only a few micrometers in size. In fact, Tagish Lake contains more of the nanodiamonds than any other meteorite.^[5]

Origin

Based on eyewitness accounts of the fireball caused by the incoming meteorite and on the photographs of the track which it had left behind and which was visible for about half an hour, scientists have managed to calculate the orbit it followed before it impacted with Earth. Unfortunately, none of the photographs captured the fireball directly. Although both eyewitness evidence and photographs of the track are usually not very accurate, it was found that the Tagish Lake meteorite had a pre-entry orbit that brought it from the outer reaches of the asteroid belt. Currently, there are only six meteorite falls with accurately determined pre-entry orbits, based on photographs or video recordings of the fireballs themselves taken from two or more different angles.

Further study of the reflectance spectrum of the meteorite indicate that it most likely originated from 773 Irmintraud, a D-type asteroid.

See also

• 773 Irmintraud, the asteroid that the Tagish Lake meteorite most likely came from.

References

• Universe: The Definitive Visual Dictionary, Robert Dinwiddie, DK Adult Publishing, (2005), pg. 222.
• Mittlefehldt, D.W., (2002), Geochemistry of the ungrouped carbonaceous chondrite Tagish Lake, the anomalous CM chondrite Bells, and comparison with CI and CM chondrites, Meteoritics and Planetary Science 37: 703-712. See summary of the article.

External links

• Tagish Lake meteorite may have held early forms of life, believe scientists
• Ancient rock star finds a home at the University of Alberta
• Researchers' website
• The Geological Society; Article/Analysis
• Brief Abstract
• Tagish Lake meteorite specimen pictures