The first analysis of data from NASA's Stardust probe has shown that comet Wild-2 is not a loose ball of icy rubble, as scientists had expected, but a solid body, pockmarked by craters and venting patchy jets of gas and dust.
The analyses, reported in the journal Science, reveal a hard but very brittle surface covered with remarkably debris-free craters, 300-foot-high mesas and pinnacles, as well as an unexpectedly large number of narrow jets spewing into space.
The results have forced scientists to revise their notions that comets are conglomerations of space debris.
"We were totally stunned by what we saw," said Donald Brownlee of the University of Washington in Seattle, the principal investigator for the National Aeronautics and Space Administration's mission.
Launched in 1999, the Stardust probe passed within 150 miles of the comet in January, sending back data on the gas and dust in the tail, as well as the most detailed pictures of a comet's surface to date.
Scientists have been anxiously awaiting the analysis because comets are some of the oldest members of the solar system. Understanding their makeup could change the understanding of the solar system's formation and possibly the beginnings of life on Earth.
The researchers were "astonished and intrigued" by the unexpected terrain of Wild-2, Brownlee said.
Unlike craters on the moon, those on Wild-2's surface are sharply defined, many having nearly vertical cliff-like walls and lacking much dust or debris. Some appear to have gouges down the walls, apparently from falling rocks, but the rocks that should be at the bottom are gone, possibly because the comet does not have enough gravity to keep material on its surface, Brownlee said.
Stardust caught thousands of particles from the comet's tail, a few hundredths of an inch across or smaller, and is bringing them back to Earth for analysis. They will parachute into the Utah desert in January 2006.
The Los Angeles Times is a Tribune Publishing newspaper.