Four years ago, NASA's Stardust spacecraft chased down a comet and collected grains of dust blowing off its nucleus. When the spacecraft Comet Wild-2 returned, comet dust was shipped to scientists all over the world, including University of Minnesota physics professor Bob Pepin. After testing helium and neon trapped in the dust specks, Pepin and his colleagues report that while the comet formed in the icy fringes of the solar system, the dust appears to have been born close to the infant sun and bombarded by intense radiation from these and other gases before being flung out beyond Neptune and trapped in the comet. The research appears in the Jan. 4 issue of the journal Science.