Pieces of a comet returned to Earth by NASA's Stardust spacecraft apparently formed near the Sun or around another star before being flung to the outer edges of the solar system, mission scientists said March 13.

Researchers found that the mineral samples of Comet Wild 2 embedded in Stardust's gel-filled collector formed under extremely high temperatures -- such as those near a star -- and not in the frigid cold expected at the solar system's edge, where most short-term comets originate.

"In the coldest part of the solar system we've found samples that formed at extremely high temperatures," said Donald Brownlee, Stardust's principal investigator at the University of Washington in Seattle, during a March 13 press conference. "When these minerals formed they were either red-hot or white-hot grains, and yet they were collected in a comet, the Siberia of the solar system."

The finding, which was announced on the 20th anniversary of the European probe Giotto's rendezvous with Comet Halley in 1986, perplexed Stardust researchers and added a new wrinkle in astronomers' understanding of how comets -- and possibly the solar system -- formed.