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 The Stardust robotic spacecraft was launched in 1999 to fly by a
comet and collect samples from Comet Wild 2 (pronounced "Vilt 2")
and parachute them back to Earth in 2006. Before reaching the comet,
the spacecraft also twice opened a collection tray to fish for
particles that may have come into the solar system from interstellar
space.
Now, after a Herculean effort involving thousands of volunteer
researchers, scientists say they have what they believe are the
first seven specks of freshly plucked dust hailing from exploded
stars and other cosmic phenomena beyond the solar system.
The grains, described in a paper in this week's edition of the
journal, Science, are unexpectedly diverse in shape, size and
content, indicating that interstellar dust likely has a more complex
and varied evolution than originally thought, said lead author
Andrew Westphal, a physicist with the University of California
Berkeley's Space Science Laboratory.
Two of the particles are bigger than the rest, though that is a very
relative term when speaking of specks that are about 4 microns, or
one-16,000th of an inch (0.0004 cm) across.
These two dust grains, which appear fluffy, like snowflakes, contain
a magnesium-iron-silicate mineral called olivine, a hint that they
may have come from disks around other stars before being altered by
interstellar travel, Westphal said.
Some of the interstellar grains also may have organics, added space
scientist Michael Zolensky, who oversees NASA's collection of
extraterrestrial samples at the Johnson Space Center in Houston.
Scientists hope to tease out more information from the dust motes,
but not quite yet. They say more sophisticated equipment and
processes are needed to analyze the tiny samples without destroying
them.
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"The prudent thing is just to put these away for a while and then
wait until better techniques come along to make the analysis,"
Zolensky said.
In the meantime, the volunteer effort to find other potential
interstellar grains in Stardust's collection trays continues. The
particles were trapped in a smoke-like substance called aerogel, but
their telltale impact tracks are so tiny that scientists had no
choice but to recruit volunteers to assist in the search.
"This takes real effort," Westphal said. "You're not just launching
your computer off on a project. You're having to do it yourself."
So far, about 30,700 self-described "dusters" have collectively done
more than 100 million searches for interstellar dust particles by
scanning digitized images of Stardust's translucent aerogel
collectors.
The next phase of the Stardust@home project starts on Friday.
(Reporting by Irene Klotz; Editing by Sandra Maler)
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