Comet particles shed light on solar system's birth spasms

Washington, Nov 18 : With the help of a few tiny particles from a comet, scientists are tracking the violent convulsions in the giant cloud of gas and dust that gave birth to the solar system 4.5 billion years ago.

These convulsions flung primordial material billions of miles from the hot, inner regions of the gas cloud that later collapsed to form the sun, out into the cold, nether regions of the solar system, where they became incorporated into an icy comet.

"If you take a gas of solar composition and let it cool down, the very first minerals to solidify are calcium and aluminum-rich," said Steven Simon, Senior Research Associate in Geophysical Sciences at the University of Chicago.

Comet Wild 2, which the scientists are studying, contain these and other minerals formed at high temperatures.

"That's an indication of transport from the inner solar system to the outer solar system, where comets are thought to have formed," said Simon.

Either turbulence within the nebula, or a phenomenon called bipolar outflow from the early sun could account for the long-distance transport of cometary material, according to Simon and his co-authors.

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.

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, Lawrence Grossman, Professor in Geophysical Sciences at the University of Chicago, and collaborators identified all three particles described in the 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.

The three particles were named Inti, Inti-B and Inti-C, after the Incan sun god.

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.

ANI