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One Comet's Torrid Tale

Irene Klotz, Discovery News

Photos

One Wild Ride

Jan. 4, 2008 -- Comet Wild 2, which was sampled by the Stardust science probe, may have formed and spent much of its life in the solar system's deep freezer, but about 10 percent of its body comes from particles forged in the hot cloud of gas and dust that surrounded the infant sun.

The finding is based on analysis of extracted gases from bits of comet particles that were returned to Earth two years ago. The dust apparently came from the solar nebula, where it was bombarded with heavily ionized helium and neon before being flung beyond Neptune's orbit and incorporated into the comet's body.

"The particles probably came from the first million years -- or even less -- of the solar system's existence," said Robert Pepin, a University of Minnesota physicist and lead author of a paper on the discovery in this week's issue of Science.

"That would be close to 4.6 billion years ago. If our middle-aged sun were 50 years old, then the particles were born in the first four days of its life," he added.

How the specks were transported hundreds of millions of miles from their birthplace is unknown. Scientists believe Wild 2 (pronounced "vilt" 2) formed in the Kuiper Belt region, a frozen domain that spans the far reaches of the solar system.

A 1974 encounter with Jupiter changed Wild 2's orbit, bringing it into the inner solar system, where it eventually caught the eye of scientists planning the Stardust sample return mission. The spacecraft flew within 150 miles of the comet's nucleus in 2004, trapping particles spewing off its body in a concoction of whipped air known as aerogel.