51³Ô¹ÏºÚÁÏ

Contrary to a popular scientific notion, there was enough mixing in the early solar system to transport material from the sun's sizzling neighborhood and deposit it in icy deep-space comets. First results from the Stardust mission, which brought samples of comet dust back to Earth, show that material near the sun traveled to the edge of the solar system, beyond Pluto, as the planets were born.

"As the solar system formed 4.6 billion years ago, material moved from the innermost part to the outermost part. I think of it as the solar system partially turning itself inside out," said Donald Brownlee, the University of Washington astronomer who is principal investigator for Stardust. The results are published Dec. 15 in a series of papers in Science.

Nigel Browning, professor of chemical engineering and materials science at 51³Ô¹ÏºÚÁÏ Davis and at the Lawrence Livermore National Laboratory, and graduate student Miaofang Chi are among the 183 authors on the primary paper. With John Bradley at the Livermore laboratory, they were able to use some of the most powerful electron microscopes in the world to study the structures and composition of particles retrieved by Stardust.

Among the biggest surprises was finding that as much as 10 percent of the material must have come from the hottest part of the solar system, Brownlee said. Scientists had expected that comets were made mostly of interstellar dust and ice. But the particles included all kinds of different mineral structures, such as silicates and nitrides, which need high-temperature gradients to form, said Browning.

NASA's Stardust mission was launched in February 1999 and met Comet Wild 2 beyond the orbit of Mars in January 2004. Stardust caught comet particles in a very light, spongy material called an aerogel. After a 2.88 billion-mile journey, Stardust returned to Earth last January with a payload of comet dust.

The work was also presented Dec. 14 at the fall meeting of the American Geophysical Union in San Francisco.