Comet particles provide glimpse of solar system's birth spasms

Bipolar outflow results when the rotating disks that surround developing new stars jet gas from their polar regions, which astronomers have observed telescopically. "That's part of the so-called X-wind model, which is somewhat controversial," Simon said.

The controversial aspect of the X-wind model is the claim that the process would produce the kind of granules that Simon and his colleagues have now identified in comet Wild 2. Another less likely possibility: The cometary material in question may have formed around another star of composition similar to the sun, then drifted into the outer reaches of the solar system. There it became incorporated into comet Wild 2.

The extraterrestrial dust particles that Simon and his colleagues examined were among thousands that NASA's Stardust spacecraft collected from comet Wild 2 in January 2004. Two years later, Stardust became the first mission to return samples of a comet to Earth.

Simon, Grossman and collaborators identified all three particles described in the Meteoritics study as pieces of a shattered refractory inclusion, one of the most unusual and informative materials discovered in early analyses of the Wild 2 samples. Such inclusions, found in some meteorites, formed by condensation from the gas in the solar nebula at temperatures of more than 2,500 degrees Fahrenheit early in the history of the solar system.

Microscopically magnified image of track 25, created by a particle from comet Wild 2 during its capture in aerogel, more informally known as "solid smoke. " Four cometary particles are circled,... Click here for more information.

The three particles were named Inti, Inti-B and Inti-C, after the Incan sun god. The original, unbroken particle would have measured no more than 30 microns across, much narrower than a human hair.

As Simon, Grossman and a team of colleagues reported in 2006, Inti contains a suite of minerals that likely were forged in fiery conditions found deep inside the cloud of gas and dust that formed the sun, Earth and the planets. And yet comets probably formed in the outer reaches of the solar system, far beyond Neptune.