[meteorite-list] Stardust Findings Override Some Commonly Held Astronomy Beliefs

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 15 Dec 2006 09:32:12 -0800 (PST)
Message-ID: <200612151732.JAA21595_at_zagami.jpl.nasa.gov>

http://uwnews.washington.edu/ni/article.asp?articleID=28836

Stardust findings override some commonly held astronomy beliefs
University of Washington
December 14, 2006

CONTACT: Vince Stricherz (vinces at u.washington.edu)
206-543-2580

Contrary to a popular scientific notion, there was enough mixing in the
early solar system to transport material from the sun's sizzling
neighborhood and deposit it in icy deep-space comets. It might have been
like a gentle eddy in a stream or more like an artillery blast, but
evidence from the Stardust mission shows that material from the sun's
vicinity traveled to the edge of the solar system, beyond Pluto, as the
planets were born.

"Many people imagined that comets formed in total isolation from the
rest of the solar system. We have shown that's not true," said Donald
Brownlee, the University of Washington astronomer who is principal
investigator, or lead scientist, for Stardust.

"As the solar system formed 4.6 billion years ago, material moved from
the innermost part to the outermost part. I think of it as the solar
system partially turning itself inside out," said Brownlee, the lead
author among 183 on the primary paper detailing the first research
results from the Stardust mission, published in the Dec. 15 edition of
the journal Science.

Brownlee is a coauthor of the other six papers on Stardust results being
published in Science, which also are the subject of a news conference
and scientific presentations at the fall meeting of the American
Geophysical Union in San Francisco.

The National Aeronautics and Space Administration's Stardust mission was
launched in February 1999 and met comet Wild 2 (pronounced Vilt) beyond
the orbit of Mars in January 2004. The comet formed more than 4.5
billion years ago and had remained preserved in the frozen reaches of
the outer solar system until 1974 when a close encounter with Jupiter
shifted the comet's orbit to a path between Mars and Jupiter. After a
2.88 billion-mile journey, Stardust returned to Earth last January with
a payload of thousands of tiny particles from Wild 2.

Among the biggest surprises, Brownlee said, was finding material that
formed in the hottest part of the solar system.

"If those materials had gotten any hotter they would have vaporized," he
said. "The most extreme particle was the second one we worked on in my
lab. These types of particles are among the oldest things in the solar
system."

That particle was a calcium-aluminum inclusion, a rare material seen in
some meteorites and the very type of matter that scientists used as an
argument for flying Stardust to less than 150 miles from Wild 2. At that
close range, the fast-moving particles could have seriously damaged the
spacecraft, but Brownlee and others felt it was necessary to take that
risk if they were to have a chance to determine an upper limit of
material that formed near the sun that ended up at the farthest fringes
of the solar system.

"Truthfully, we really didn't expect to find anything from the inner
solar system. Instead, it showed up in the second particle we looked
at," he said. The scientists also found magnesium olivine, a primary
component of the green sand found on some Hawaiian beaches and, like a
calcium-aluminum inclusion, one of the first things to form in the
cooling solar nebula.

Brownlee estimates that as much as 10 percent of the material in comets
came from the inner solar system. "That's a real surprise because the
common expectation was that comets would be made of interstellar dust
and ice."

But interstellar dust has a glassy characteristic, he said, while the
particles that formed around stars and are found in comets are partially
crystalline. It was suggested previously that interstellar dust had been
mildly heated to transform its glassy substance into the crystalline
comet contents.

"What we've seen, I believe, is totally incompatible with that
interpretation," Brownlee said. "The particles we've seen have been
heavily heated. Astronomical interpretations will be affected by that."

Wild 2's characteristics seem to be different from those of comet Tempel
1, which was closely examined in a mission called Deep Impact. In that
case, a probe crashed into the comet surface and the properties of the
resulting dust were analyzed using the infrared part of the spectrum.
But Brownlee notes that while Tempel 1 was examined remotely from a
distance, Stardust returned actual samples for scientists to study.

"The comets may be different from each other, or different observations
could simply be a result of the different techniques used to examine
them. It is a challenge for us to understand how they are different and
why," he said.

Besides the UW, other major partners for the $212 million Stardust
project are NASA's Jet Propulsion Laboratory, Lockheed Martin Space
Systems, The Boeing Co., Germany's Max-Planck Institute for
Extraterrestrial Physics, NASA Ames Research Center, the University of
Chicago, The Open University in England and NASA's Johnson Space Center.

Brownlee has noted the irony that the tiny specks of comet dust are
being examined by some of the largest investigative tools, such as the
2-mile-long Stanford Linear Accelerator. But with more than 150
scientists studying dust from Wild 2, Stardust also is driving the
advance of new technology, including development of the world's
highest-resolution microscope at the Lawrence Livermore National
Laboratory.

"We're doing things no one ever imagined we could do, even at the time
we launched the mission," Brownlee said. "We've taken a pinch of comet
dust and are learning incredible things."

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Received on Fri 15 Dec 2006 12:32:12 PM PST