Dec. 14, 2006 — Comets may live most of their lives in the solar system's
deep-freeze, but it wasn't always that way.
The results from the first mission to return a comet sample show that
mixed in with the ice and interstellar dust grains that many
scientists expected to find are particles forged in the
nuclear fires of the inner solar nebula.
"We found that the comet is a real grab-bag of stuff that must have
formed in many different environments, including very close to the
sun," said Michael Zolensky, a NASA scientist at the Johnson Space
Center in Houston and a co-author in a series of papers about the
Stardust mission that appear in this week's Science.
NASA dispatched a probe in 2004 that, two years later, flew by
Comet Wild-2 to trap samples popping off the comet's core. The return
capsule parachuted to Earth in January.
The Stardust science team invited experts from around the world to
participate in the analysis, resulting in an early
and thorough first look at what the comet samples contain.
The prevailing theory had been that comets were made of particles
found in the outer regions of the solar system: ices, cold minerals,
bits of matter from exploded stars.
Instead the searchers found particles that formed throughout the
solar nebula, including the super-heated regions near
the sun.
Stardust lead scientist Donald Brownlee, with the University of
Washington, estimates about 10 percent of Comet Wild-2 contains
material forged in the hottest parts of the solar system.
