HOUSTON: Particles from an icy comet that were collected and returned to Earth aboard a NASA science satellite show dozens of minerals that form only in extreme heat a finding that complicates theories about how the solar system formed, scientists said on Monday.

Prevailing theories about the solar system's formation cannot explain how this high-temperature material ended up in the frigid regions beyond Neptune's orbit, the so-called Kuiper Belt where comets formed.

"Remarkably enough, we have found fire and ice," said Stardust principal investigator Donald Brownlee, with the University of Washington. "We've found samples from the coldest part of the solar system that have mineral grains formed under extremely high temperatures."

The grains include an exotic titanium-vanadium-nitrogen blend that forms in temperatures higher than 1,100 degrees C.

The discovery leads scientists to two possible conclusions: Either the minerals formed in the hottest, innermost region of the nebula that eventually became our solar system, or they came from another star.

"If it was formed in our solar system, then it had to be transported from the hottest regions to the coolest," Brownlee said.

Scientists estimate the minerals would have had to be closer to the Sun than Mercury to form and they would have had to be flung more than 45 times the distance of Earth to the Sun to reach the Kuiper Belt region where the comets were born.

Researchers plan extensive studies to determine the chemical histories of the sample particles, which eventually will reveal whether the grains were heated by the Sun or another star.

"We will know soon," Brownlee said at the annual Lunar Planetary Institute's science conference, which opened on Monday in Houston.

The Stardust science spacecraft was launched in February 1999 and flew by Comet Wild-2 on January 2, 2004, on a mission to retrieve samples for analysis. A capsule containing the comet samples parachuted to Earth two months ago.

In addition to learning about how the solar system formed, scientists hope the Stardust samples will shed light on a theory that comets supplied primitive Earth with the organic materials needed for life.

NASA astrophysicist Scott Sandford, with the Ames Research Center in Moffett Field, California, said it is excruciatingly difficult to sort out cosmic organic matter from terrestrial elements, but at least one sample from the Stardust collection seems to contain indigenous carbon and hydrogen.

Chemical analysis of the sample shows high ratios of deuterium, a hydrogen isotope that is double the mass of ordinary hydrogen due to a neutron in the nucleus. "We take this as a pretty promising sign, but we need more work," Sandford said.

Agencies

(China Daily 03/15/2006 page1)