After the Tagish Lake meteorite crashed to earth in northern British Columbia in January 2000, it was hailed as the most primitive and pristine material from anywhere in the solar system examined so far. Now two reports published online by the journal Science shed more light on its origins and composition.
Sandra Pizzarello of Arizona State University at Tempe and her colleagues analyzed the organic compounds sealed within the carbon-rich space rock. They found many of the same compounds seen in similar meteorites, a class known as carbonaceous chondrites, but in a different distribution. The most striking difference, the researchers say, was a near absence of amino acids, which have been found in previous meteorites. "Some people have been disappointed that we found virtually no amino acids, but scientifically this is very exciting," Pizzarello says. "This meteorite shows the complexity of the history of organic compounds in spaceit seems to have had a distinct evolution."
In the second study, Takahiro Hiroi and Carle Pieters of Brown University, together with Michael Zolensky of NASAs Johnson Space Center, suggest an origin for the Tagish Lake meteorite. Most meteorites are believed to come from asteroids or extinct comets, the researchers say, but there are several asteroids for which meteoritic counterparts have not been found. They counted D-type asteroids among this group until now. The reflectance spectrums of two chips from the Tagish Lake meteorite, the scientists say, suggest it is derived from a D-type asteroid. Found in the outer solar system beyond the main asteroid belt, D-type asteroids contain some of the oldest raw materials of our solar system.
Indeed, the team lead by Pizzarello also found fullerenesenclosed spheres made up of 60 carbon atomscontaining helium and argon in a ratio indicative of the early history of the solar system. "Overall," she says, "Tagish Lake represents a simpler, more unaltered stage than we have seen before."