now this is cool.
http://www.nytimes.com/2006/12/15/science/space/15comet.html?_r=1&ref=us&oref=sloginWASHINGTON, Dec. 14 — Comets are not all made of interstellar dust and ice, but instead may contain material shot from the heart of the solar system during its tumultuous birth, scientists reported Thursday after examining pristine particles of a comet that were brought back by the Stardust spacecraft.
The evidence suggests that comets did not form in isolation in the outer parts of the solar system as it coalesced from a swirling mass of primal material, the researchers said. Instead, they said, some of the hot material that formed planets around the Sun seems to have spewed off into distant areas and become a component of distant comets.
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“Comet dust seems to be a real zoo of things; we see all kinds of particles that are clearly formed at different places, possibly at different times and certainly under different conditions,” said Scott Sandford of the NASA Ames Research Center in California, who was the lead author of one of the papers.
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Material from comet Wild 2 has mineral characteristics that appear to be different from those observed in comet Tempel 1. In that case, involving a spacecraft called Deep Impact, a probe crashed into Tempel 1’s surface in July 2005, and the properties of the resulting dust were analyzed by the spacecraft and distant telescope observations. Dr. Brownlee noted that whereas Tempel 1 had been examined from a distance, Stardust had returned actual samples for scientists to study.