[meteorite-list] Comet's Dust Seen As Key To Life; Stardust Will Carry Sample To Earth

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Jun 25 12:23:36 2004
Message-ID: <200406251623.JAA18054_at_zagami.jpl.nasa.gov>

http://www.kentucky.com/mld/kentucky/news/nation/8975443.htm

Comet's dust seen as key to life; probe will carry samples to Earth

BY ANDREAS VON BUBNOFF
Chicago Tribune
June 21, 2004

CHICAGO - (KRT) - Organic chemicals found on a comet may support the
idea that ancient cosmic collisions helped spur the origins of life on
Earth, scientists said as they presented data from a probe that passed
within 147 miles of comet Wild 2 earlier this year.

The probe, called Stardust, is bringing back to Earth the first dust
samples ever returned from a comet. But recent data and pictures also
give detailed clues about the comet's anatomy that indicate it is
surprisingly different from comets studied before.

Comets offer unique insights into the formation of the solar system
because they contain material that has changed little since the sun and
planets formed more than 4 billion years ago. They are essentially dirty
snowballs, composed mostly of frozen water and dust, and they are
visible only when their orbits take them near the sun. The sun's heat
causes jets of dust and water vapor to burst from the comet's surface -
forming the comet's tail.

Because the young Earth was too hot for many organic molecules to last
for long, some experts have proposed that impacts by comets in a later
period may have seeded the planet with some of life's chemical building
blocks.

"We don't expect that life came from comets," said Donald Brownlee, the
leading scientist of the Stardust mission. "But we do expect that the
molecules used by life probably came from comets and asteroids."

That theory gained support from Stardust data analyzed by a German team
led by Jochen Kissel. Their findings appear in Friday's edition of the
journal Science along with three other papers on the comet probe,
including one by University of Chicago scientists.

Kissel's group used instruments on the probe to analyze dust near Wild 2
and found an organic compound called PQQ that had never been detected in
a comet. Researchers believe PQQ plays a key role in cell growth.

"PQQ is found in (almost) every cell of every living entity on earth,"
Kissel said.

In addition to its chemical findings, Stardust obtained the highest
resolution photos ever taken of the solid part of a comet, called the
core. The comet was riddled with craters, which scientists said
indicates that Wild 2's original surface has not been burned away by the
sun.

Named after the Swiss scientist who discovered it, Wild 2 (pronounced
"vilt two") entered the inner realm of the solar system only recently,
in 1974, after a close encounter with Jupiter changed its orbit. Only
then did the comet's ancient core start losing material to the heat of
the sun.

"We were expecting craters," Brownlee said. "Craters mean that some of
(Wild 2's) surface is really old."

Yet the craters and structures were unlike anything seen before on the
surface of comets, the researchers said.

"We were totally stunned by what we saw," Brownlee said, describing
craters with almost vertical walls. "The vertical walls are amazing
because if the comet were made of a powdery material, you couldn't
support vertical surfaces."

Many scientists had thought of comet cores as fragile, said Claudia
Alexander, project scientist at NASA's Jet Propulsion Laboratory in
California. Other comets seemed so tenuous that they fell apart easily,
as when comet Shoemaker-Levy 9 broke up as it approached Jupiter in
1994. But Wild 2's craters suggest its composition is more solid.

Scientists were also surprised to see that the comet had about 20 jets
coming from its surface.

"We thought that there would be maybe one jet," said Benton Clark, chief
scientist of space exploration systems at Lockheed Martin.
Received on Fri 25 Jun 2004 12:23:22 PM PDT