Pieces of a
comet returned to Earth by NASA's Stardust
spacecraft apparently formed near the Sun or around another star altogether before
being flung to the outer edges of the Solar System, mission scientists said
Monday.
Researchers
studying samples of Comet
Wild 2 (pronounced "Vilt 2") embedded in Stardust's gel-filled collector found
that the minerals formed under extremely high temperatures - such as those near
a star - and not in the frigid cold expected at the Solar System's edge, where
most short-term comets originate.
"In the
coldest part of the solar system we've found samples that formed at extremely
high temperatures," said Donald Brownlee, Stardust's principal investigator at
the University of Washington in Seattle, during a Monday press conference. "When
these minerals formed they were either red hot or white hot grains, and yet
they were collected in a comet, the Siberia of the Solar System."
The finding
- announced on the 20th anniversary of the European probe Giotto's rendezvous
with Comet
Halley in 1986 - perplexed Stardust researchers and added a new wrinkle in
astronomers' understanding of how comets, and possibly the Solar System,
formed.
Particle
science
NASA's
Stardust sample return capsule landed
in the Utah desert on Jan. 15, 2006 after a nearly seven-year mission to
retrieve comet and interstellar dust particles in an aerogel
collector. The probe swung
past the 4.5 billion-year-old Comet Wild 2 on Jan. 2, 2004.
Astronomers
aren't sure whether the minerals found in Stardust's comet samples formed near
the Sun or around another star, though isotope scans are expected determine
that for sure in upcoming tests, Brownlee said. Olivine, a mix of iron and
magnesium that appears green on some Earth beaches, is one of the several
surprising compounds found in the Wild 2 samples, he added.
Michael
Zolensky, Stardust curator and a mission co-investigator at NASA's Johnson
Space Center (JSC), said astronomers believed that a sort of material "zoning"
occurred during the Solar System's formation.
According
to the model, substances formed under hotter temperatures closer to the Sun,
while colder materials - such as the gases that make up the giant planets -
took root further out, he added.
But if
Stardust's comet samples are found to be local to the Solar System, and not
from some distant start, they'd suggest a sort of transportation system to
fling particles formed near the Sun out past the orbit of Pluto
and into the comet realm, researchers said.
"If this
mixing is occurring, as suggested by these results, than how do you preserve
any kind of zoning in the solar system," Zolenksy said. "It raises more
mysteries."
Awash in
samples
Thanks to
the Stardust mission, astronomers have a wealth of comet and dust samples at
their disposal, at least 45 of which large enough to be seen with the naked
eye. But the number of actual samples could range in the millions, researchers
said.
"We're just
learning how to handle the samples, how make the best use of them," Zolensky
said. "Once we understand that then we'll open them up for widespread analysis.
And that will go on for the rest of our lives."
Stardust
researchers said that all of the probe's 132 sample cells contain comet
particles ranging in size between 15 micrometers - less than the width of a
human hair - down to about one micrometer, though the interstellar dust samples
are much smaller. The largest of those dust samples can reach one micrometer,
they added.
"With every
day that goes by, we're able to handle smaller particles, so hopefully a year
from now we'll be able to handle things down to a half a micrometer," Zolensky
said.
Mission scientists
expect to scan Stardust's sample cells and release them to the Stardust@home
project, an effort that allows the public to search for comet and dust samples
using their personal computers, in a few weeks.
Researchers
also hope to pin down the origin of Comet Wild 2's high-temperature forming
minerals in the next few weeks as well.
"It's a
really exciting mystery story," Brownlee said of the new Stardust findings. "So
stay tuned."
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