http://www.cnn.com/2001/TECH/space/08/23/meteorite.origin/index.html
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Source of oldest, rarest meteorite found

                 August 24, 2001 Posted: 7:45 AM EDT (1145 GMT)

                                              By Richard Stenger
                                              CNN 

                                              (CNN) -- A mysterious space rock
                                              that defies conventional
                                              classification contains material that
                                              predates the solar system, and
                                              likely came from the outer edge of
                                              the asteroid belt, scientists said
                                              Thursday. 

                                              The alien boulder stunned onlookers
                                              last year when it streaked over Canada,
                                              exploded into a giant fireball and
                                              slammed into a frozen lake in the
                                              Yukon. 

                                              The landing site helped keep preserve
                                              the fragile remnants of the space rock,
                                              including frozen volatile gases that
                 otherwise might have evaporated. 

                 "This meteorite turned out to be the most primitive meteorite we know," said
                 Brown University planetary geologist Takahiro Hiroi, lead author of a report in
                 the August 24 edition of the journal Science. 

                 The Tagish Lake meteorite resembles space rocks known as carbonaceous
                 chondrites, but contains much more carbon and pre-solar grains, which predate
                 the solar system. 

                 "It contains more pre-solar grains than any other meteorites," Hiroi said. 

                 Pre-solar grains, which predate the birth of the solar system 4.6 billion years
                 ago, were produced in the fiery death of an ancient star. The explosion provided
                 the raw materials for our sun and planets, according to scientists. 

                 Most of the building blocks of our solar system vaporized and reformed, but
                 pre-solar grains never melted. 

                 The Tagish Lake rock fragments match
                 nothing found on Earth. But Hiroi and
                 colleagues at Brown and NASA
                 analyzed their chemical fingerprint and
                 determined that the meteorite came
                 from a particular class of space
                 boulders, the oldest known, in the
                 asteroid belt between Mars and Jupiter. 

                 Hiroi is hardly surprised that such
                 meteorites have not been recovered
                 before. Few of the D-type asteroids
                 reside in areas where space rocks
                 collide and produce fragments that
                 might drift to Earth. And the rare D-type meteorites that reach our atmosphere
                 likely burn up completely because they are so fragile. 

                 "This particular meteorit e was so big and had a soft landing on ice and snow.
                 That may be why it survived," he said. 

                 On January 18, 2000, the 250-ton Tagish Lake monster stunned British
                 Columbia onlookers when it ignited into a giant fireball and produced the
                 explosive equivalent of 5 to 10 tons of TNT, according to Purdue University
                 researchers.