SAN FRANCISCO (AP) - Detailed observations from the first comet samples returned to Earth are debunking some of science's long-held beliefs on how the icy, celestial bodies form.

Scientists expected the minute grains retrieved from a comet Wild 2 to be made up mostly of interstellar dust - tiny particles that flow through the solar system thought to be from ancient stars that exploded and died.

Instead, they found an unusual mix of primordial material as if the solar system had turned itself inside out. Hot particles from the inner solar system migrated out to the cold, outer fringes beyond Pluto where they intermingled and congealed to form a comet.

"People imagine that comets form in total isolation, which is definitely not true," said Don Brownlee, a University of Washington astronomer who is the principal scientist for the $212 million Stardust mission.

Brownlee estimated that up to 10 percent of materials in comets may come from the inner solar system.

A series of papers detailing the first scientific results from the Stardust mission were to be published Friday in the journal Science and presented at an American Geophysical Union meeting Thursday.

A capsule carrying thousands of minuscule samples from comet Wild 2 returned to Earth last January after looping around the sun to capture the interstellar and comet debris and swooping past Wild 2 to scoop up dust...