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.
The measurements were made using five different extraction and analytical methods. The findings were compared with other materials of extraterrestrial origin, such as micrometeorites and interplanetary dust grains.
"One of the surprises in samples collected from an icy object forming, and, for much of its lifetime, residing in the cold outer reaches of the solar system, was the discovery that many of its constituent particles are igneous, refractory 'rocklets' processed at very high temperatures, presumably close to the sun before transport to the outer nebula and incorporation into Wild 2," Pepin and colleagues wrote in their paper.
Scientists are keenly interested in understanding what comets are made of, since they are believed to be the supplier of organic molecules and other materials to planets.
"We want to establish what the solar system looked like in the very early stages," Pepin said. "If we establish the starting conditions, we can tell what happened in between then and now."
Related Links:
our sites
video
mobile
shop
stay connected
corporate
