Tagish Lake Meteorite Analysis Provides Glimpse of Early Solar System
On the morning of 18 January 2000, a small asteroid slammed into the Earth’s atmosphere over northwestern North America. Hundreds of thousands of people witnessed its last moments – as did American military satellites. When correlated together, these observations made it easy to pinpoint a debris zone.
As the object approached the Earth’s surface the shock of entering the atmosphere caused it to shatter into many pieces. A sizeable portion of the meteorite’s fragments landed on an ice-covered lake in British Columbia – Lake Tagish – and were quickly encased in ice.
Despite a rather clear idea where pieces would have hit the Earth, it was several months before fragments were located and identified. Eventually, more than 500 fragments were recovered – many from the ice covering Lake Tagish. Not only was the entrapment in ice fortuitous for meteorite hunters who would arrive to locate the pieces months later, it was also a boon to those who would later study the fragments. A dedicated amateur had the foresight to exercise extreme care in collecting the meteorite samples – including keeping them encased in the ice within which they had come to rest. His actions were to allow others to open a door into an early portion of our solar system’s history.
The Lake Tagish meteorite, as it was later to be named, is a carbonaceous chondrite, a comparatively rare type of meteorite rich in organic compounds. By virtue of having been encased in ice almost instantly upon arrival on Earth, the chance of terrestrial contamination was dramatically reduced. Moreover, despite its blazing descent into our atmosphere, some of the materials within the meteorite may never have been appreciably warmed from their long term refrigeration in interplanetary space. As such, their potentially pristine condition held out the promise of an unusual glimpse into the structure of its parent body – and that of the early solar system.
After months of study in laboratories around the world, many of the hopes pinned on the examination of this unusual specimen have come to fruition.
Scientists at Purdue University have presented a paper at the Meteoritical Society’s annual meeting in Chicago last week detailing the results of their analysis of fragments of the Lake Tagish meteorite.
For starters, the meteorite is 4.5 billion years old – dating from the time when the Earth was forming. While it was readily categorized as a carbonaceous chondrites, detailed analysis shows it to have unusual chemical properties – properties that suggest that it originated in a portion of our solar system heretofore unexamined.
According to a Purdue University press release Purdue Chemistry Professor Michael Lipschutz says “this meteorite is unique, and represents a new kind of planetary material. From the chemical composition, it’s reasonable to
assume it came from parts of the solar system different than the ones that produced other carbonaceous chondrites previously studied.” Lipschutz says the oxygen isotopes in the sample place the Tagish Lake meteorite somewhere between the subtypes called CI and thermally metamorphosed CM, putting the sample in a class by itself. “Thermally metamorphosed meteorites came from parts of their parent bodies that went through some type of major heating experience that caused some volatile elements to vaporize,” he says. “The fact that it’s not thermally metamorphosed means that this meteorite is much more closely related to the CI meteorites than to any other kind of meteorite.”
According to Lipschutz “CI meteorites are considered a “measuring stick” of sorts in cosmochemistry because they contain a chemical composition similar to the outside surface of the Sun. The Tagish Lake meteorite is, in fact, a sample of the pre-solar nebula, out of which the planets formed. We have never before had a sample of this material.”
Related Links
° Primordial Meteorite in a Class by Itself, press release, Purdue University, 1 September 2000
° Largest meteorite find in Canadian history, University of Calgary press release, 31 May 2000
° DOD 20-001 Fireball Detection (over Canada), 19 January 2000
° Yukon Meteorite May Provide “New Window Into the Universe”, NASA Press release, 16 March 2000
° Tagish Lake Description, Meteoritical Bulletin
Background Information
° Meteorite Found to Contain Water From Our Solar System’s Infancy, SpaceRef
° Meteorites, SpaceRef Directory
° Meteorite and Impacts Advisory Committee to the Canadian Space Agency, University of Quebec.
° Catalog of Canadian Meteorites. University of Calgary
