[meteorite-list] Comet Dust Sparks Scientific Intrigue

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Feb 21 11:08:29 2006
Message-ID: <200602211602.k1LG2jN17386_at_zagami.jpl.nasa.gov>


Comet dust sparks scientific intrigue

Samples hint at ancient origins, with tentative signs of organic

By Alan Boyle
February 20, 2006

ST. LOUIS - Giving a sneak peek of results to come, a top mission
scientist said flecks of material collected during the Stardust
spacecraft's seven-year journey bear the unmistakable signature of an
ancient comet, including sulfides, crystalline silicates and probably
organic compounds as well.

"We're seeing a variety of things that we know absolutely come from a
comet," University of Washington astronomer Donald Brownlee, Stardust's
principal investigator, told reporters here Monday at the annual meeting
of the American Association for the Advancement of Science.

Brownlee heads an international team of about 150 scientists who are
getting their first looks at the specks captured by NASA's Stardust
spacecraft as it flew close to Comet Wild 2 back in 2004. At the end of
a 2.9-billion-mile (4.6-billion-kilometer) round trip, the spacecraft
successfully delivered a capsule containing the samples back to Earth on
Jan. 15.

The flecks of dust and grit are contained within 132 ice-cube-sized
tiles of aerogel, an ultra-light, porous material that has been compared
to "solid smoke." As the bits entered the tiles, they carved
carrot-shaped or turnip-shaped tracks in the transparent aerogel.

Brownlee said six of aerogel blocks have been pulled out for inspection
so far. "All of the tiles are in good shape ??? which is amazing," he said.

Meeting expectations

What's even more amazing is how well the first round of analysis is
matching expectations. Brownlee and other Stardust scientists are
holding back their first formal reports for a scientific meeting in
Texas next month - but during Monday's news conference, Brownlee said
the samples studied so far contain iron sulfides and glassy material
such as crystalline silicates. Those ingredients are found in meteorites
as well.

Later, Brownlee told MSNBC.com that there were preliminary indications
of organic compounds, based on telltale infrared readings. He cautioned
that the initial indications were tentative and could still be traced to
contaminants. "The spacecraft is made of plastic, for example," he said.
But Brownlee also said it wouldn't be surprising to find organics in
comet dust.

"I would suspect that somewhere around 10 percent would be organic
particles," he said.

Scientists have known for a long time that organic compounds exist in
space, and the term shouldn't be understood to refer to a biological
source for the compounds. However, some scientists suggest organics
could have arrived on Earth from space to serve as the
building blocks for primitive life.

Checking the compounds

A co-investigator for the Stardust mission, Scott Sandford of NASA's
Ames Research Center, agreed that organic readings could be due to
contamination. "Just because we detect a compound doesn't mean it's a
cometary compound," he told MSNBC.com. But so far, he said, "it looks
like we brought back a pretty clean capsule."

Sandford said researchers are finding "little facts here and there, but
it's not falling all together," simply because it's too early to get a
comprehensive sense of the composition of the cometary dust.

Nevertheless, he said, "everybody on the team is really pleased - things
could have been a lot more complicated."

In the weeks and months ahead, Sandford and his team will be analyzing
the types of carbon found in the samples - not only to trace the
organics, but also to determine whether such compounds predated the
formation of the solar system.

Scientists say comets represent the cold leftovers from the solar
system's beginnings, 4.5 billion years ago. The Stardust samples confirm
that the material thrown off by Comet Wild 2 has not undergone chemical
change for billions of years, Brownlee said: "It's never been hot."

So far, the Stardust team has not seen firm evidence that the cometary
samples contained water - and that ingredient should be abundant in
comets, which are popularly called "dirty snowballs." Brownlee
emphasized that the water could not be detected directly. Rather,
scientists would look for the presence of hydrated minerals created by
interaction with water. "We do not see hydrated silicates, at least so
far," Brownlee said.

Solving the puzzles

Scientists at the AAAS meeting said that Stardust could eventually shed
light on many of the puzzles surrounding comets and the solar system's
formation. "Dust, lowly dust, plays a very important role in the birth
of solar systems and the death of solar systems," said Lee Anne Willson,
an Iowa State University astronomer who studies dust conditions around
dying stars.

Joe Nuth of NASA's Goddard Space Flight Center said that "Stardust
represents a very great challenge for us," and that the mission's
findings will likely rule in or rule out a variety of theories about the
nature of comets and the genesis of the solar system.

That won't all happen at once, however. Ernst Zinner, an astrophysicist
at Washington University of St. Louis, said his team was just beginning
the work of analyzing the Stardust samples for the presence of
interstellar dust. Brownlee, meanwhile, cautioned reporters that the
full findings from the $212 million Stardust mission won't sink in for a
long time.

"It will be years and years before a reasonable understanding of this
comes out," he said.
Received on Tue 21 Feb 2006 11:02:43 AM PST

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