for National Geographic News
The first ever analyses of comet dust are in, and they stand to revolutionize our understanding of the early solar system, scientists say.
The particles were collected by Stardust, a NASA probe that passed within 150 miles (240 kilometers) of comet Wild 2 (pronounced Vilt 2) to scoop up escaping debris.
(Watch a video overview of the Stardust mission.)
The probe encountered the comet between the orbits of Mars and Jupiter in January 2004 and returned to Earth two years later.
It netted approximately 10,000 dust grains—the first such samples ever retrieved from a distance beyond the moon.
One of the most interesting findings is that 10 percent of the dust appears to have originated near the sun, according to scientists.
Conventional theory has held that comets form from dust grains that had never been close to the sun.
But many of the grains brought back by Stardust contain minerals that only crystallize under extreme heat, scientists said yesterday.
"They formed in the hottest possible places in the solar system," the project's lead scientist, David Brownlee of the University of Washington, said at a meeting of the American Geophysical Union in San Francisco, California.
"It was quite stunning to find this in a body that formed in the coldest place in the solar system."
Brownlee's colleague, Michael Zolensky of NASA Johnson Space Center in Houston, Texas, likened the comet to "a big vacuum cleaner" that swept up dust from all over the solar system as it formed far beyond the orbit of Pluto.
How the inner-system dust got so far from the sun, however, is still a mystery.
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