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Comet's Dust Resembles Asteroid's

Irene Klotz, Discovery News

Photos

Captured in Lab, Not From Comet

Jan. 24, 2008 -- When scientists planned a mission to bring back samples of a comet to Earth, they expected to find bits of materials from the original building blocks of the solar system.

Instead, the samples from Comet Wild-2 (pronounced "vilt-2") returned by the Stardust science probe in 2006 contain matter that more closely resembles what is found in asteroids, concludes a team of researchers.

Wild-2 is a relative newbie to the inner solar system, bumped from its probable birthplace in the Kuiper Belt region beyond Neptune by a chance encounter with Jupiter in 1974.

With just five orbits around the sun's inner neighborhood, scientists believed the comet is relatively unaltered and is a pristine chamber filled with primordial remains.

"Wild- 2 has been widely anticipated to be a reservoir of pre-solar material, including stardust cryogenically preserved since the accretion of the planets," said Hope Ishii with the Institute of Geophysics and Planetary Physics at the Lawrence Livermore National Laboratory in California.

The Stardust team looked for two specific materials to test their theory: a silicate known as GEMS (glass with embedded metal and sulfides) and crystalline silicate enstatite. Both materials have been found in samples from Earth's upper atmosphere, which scientists believe came from comets.

But the only GEMS found in the Stardust samples were made as the comet bits crashed into the probe's aerogel-filled collection plates at 13,700 m.p.h., generating temperatures far greater than anticipated.

"Temperatures on impact were expected to reach several hundred Kelvin but exceeded 2000 K locally," Ishii and colleagues wrote in a paper about their findings in this week's Science.