Pristine comet samples returned this
weekend by the Stardust spacecraft after a 2.9-billion-mile
(4.7-billion-km) journey wildly exceeded scientists' expectations,
project managers report.
A canister containing particles trapped after the Stardust
space probe's 2004 encounter with Comet Wild-2, pronounced
as "Vilt," landed on Earth on Sunday. The samples
were taken to the Johnson Space Center in Houston for inspections.
"This exceeded all of our grandest expectations," Donald
Brownlee, a University of Washington-based researcher and
the principal Stardust investigator, told a news conference.
The team was still giddy from the smooth landing of the
Stardust capsule in the moon-lit Utah desert, but that
turned out to be just the beginning.
When the sample canister inside the capsule was opened,
scientists could see with naked eyes small black rocks
and other particles that had been trapped in the probe's
gel-filled collection device.
"We were totally overwhelmed by the ability to actually
see this so quickly and so straight-forwardly," Brownlee
said.
The samples were trapped in a substance called aerogel,
which although it has the same ingredients as a glass window
is 99.9 percent air and has the lowest density of any solid
substance.
The Stardust spacecraft lifted off seven years ago and
aimed for a close encounter with Comet Wild-2, a relative
newcomer to the comparatively warmer region of space between
the orbits of Mars and Jupiter.
The comet is believed to come from the Kuiper Belt region
beyond Neptune, but had a close approach to Jupiter in
1974 which deflected the icy body into its new orbit. Because
Wild-2 has not been circling near the sun for long, the
comet is believed to contain most of its original materials.
Scientists say comets contain leftovers from the solar
system's creation.
"We've brought back an ancient cosmic treasure from
the very edge of the solar system," Brownlee said.
Researchers are eager to study the comet samples to help
answer questions about how the Earth and its sister planets
formed and what comprised the original disc of interstellar
dust that incubated and fed the early solar system.
Comets, for example, may have seeded Earth with the organic
materials and water that eventually led to life. The same
process may have happened on other planets, such as Mars,
and may be happening today in other solar systems.
The chunks of Stardust's aerogel contain "hundreds
and hundreds and hundreds of tracks" from comet particle
impacts, some of which may even end with a few atoms of
water ice, Brownlee said.
One hole, which ends with an embedded rock,is so large,
you can nearly poke a finger in, Brownlee said.
Scientists expect to get more than 1 million particles
larger than one-millionth of a meter in diameter.
Once the samples are cataloged, NASA will begin distributing
small amounts to researchers worldwide for analysis..
