ST. LOUIS, Missouri (AP) —— Scientists said Monday they have begun slicing and dicing¹ the first of hundreds of microscopic² specks³ of comet dust, virtually unchanged since the birth of the solar system, that a NASA spacecraft successfully returned to Earth in late January.

　　Preliminary analysis shows the dust, captured when the robotic Stardust spacecraft flew past the comet Wild 2 in January 2004, is unmistakably cometary in origin, said Don Brownlee, a University of Washington astronomer⁴ who is the principal scientist for the $212 million mission.

　　As such, the grains represent pristine⁵ samples of the primitive⁶ material that came together to form the sun, the nine planets and everything else in the solar system, including human beings.

　　"We believe materials coming out of comets now is the same material that went into comets 4.5 billion years ago," Brownlee told reporters at the annual meeting of the American Association for the Advancement⁷ of Science here.

　　The initial work on the samples shows they contain glassy materials, crystals like olivine and various trace elements, Brownlee said.

　　Each tiny grain is being sliced, sometimes into hundreds of sections, for detailed⁸ analysis. Some grains are just four microns in diameter, meaning it would take 25 of them to equal the width of a human hair.

　　Eventually, each grain should tell scientists something about its birth billions of years ago in the wake of dying stars, as well as how they came together to form new stars.

　　"Dust, lowly dust, plays a very important role in both the birth of solar systems and the death of solar systems," said Lee Anne Willson, an Iowa State University astronomer.

　　The Stardust samples represent the first time a space mission has returned solid bits of extraterrestrial material since the manned Apollo 17 mission to the moon in 1972.

　　Direct study of the samples should allow astronomers⁹, who can only peer on stars from afar, and astrophysicists, who are limited in what stellar processes they can recreate in the laboratory, to confirm hypotheses they've made about how things in the universe come together and fall apart, scientists said.

　　"Stardust is going to challenge the very guesses we've made," said Joe Nuth, an astrochemist at NASA's Goddard Space Flight Center.

　　Stardust captured the comet samples in a material called aerogel, a silicon-based material that is 99.8 percent empty space. (Learn more about aerogel)

　　The particles left telltale tracks —— some shaped like carrots, others like turnips¹⁰ —— in the icecube-sized chunks¹¹ of aerogel when they struck. Each particle can take hours to remove, including through the use of a computer-controlled needle that cuts around each track, Brownlee said.

　　"It's like taking a plug out of a watermelon," he said.

　　The first major science results from the Stardust mission are expected to be presented March 13-17 at the Lunar and Planetary Science Conference outside Houston.

　　The Stardust mission is managed by NASA's Jet Propulsion Laboratory in Pasadena, California.