[meteorite-list] Stanford Examines Comet Particles

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Feb 6 14:24:32 2006
Message-ID: <200602061922.k16JMqW23014_at_zagami.jpl.nasa.gov>

http://daily.stanford.edu/tempo?page=content&id=19254&repository=0001_article

Stanford examines comet
By Kat Lewin
The Stanford Daily
February 6, 2006

Scientists at Stanford have been feeling a little spacey lately. On Jan.
15, NASA's Stardust mission touched down after a seven-year excursion
through space, bearing precious interstellar dust. The particles brought
back are now being evaluated at approximately two-dozen universities,
including Stanford as part of project Stardust_at_home.

The stardust was collected from the tail of comet WILD-2 (pronounced
"vilt"). According to Sean Brennan, a physicist at the Stanford
Synchrotron Radiation Laboratory (SSRL) physicist, this collection was
especially significant because the comet has only passed by the sun five
times.

"This is the first time we have brought back extraterrestrial materials
since Apollo, and it's the first time we've had access to pristine
meteoric material," Brennan said. "Prior to '74, WILD-2 was in orbit
outside of Jupiter, far from the sun. We were worried that everything
we'd been looking at had been processed by the sun. What you really want
to do is fly out past Jupiter and grab one of those rocks."

The limited exposure to the sun differentiates the particles from
meteorites that have been studied in the past, explained third-year
chemistry graduate student Maegan Spencer, who will also be studying the
space dust.

"When a meteorite falls to Earth it's so hot it forms a fusion crust,"
Spencer said. "The rock melts and preserves everything in it."

Spencer and Brennan are both part of collaborative preliminary
examination team comprised of about 150 scientists all over the world,
Spencer explained. This team will have exclusive access to the particles
until September 2006, according to Brennan, and will analyze aspects of
the dust ranging from bulk chemistry to isotopes to amino acids and
organic compounds. Among the first institutions to have access to these
particles are a BayPac consortium of approximately 15 to 20 scientists
from the Stanford Linear Accelerator Center (SLAC), UC-Berkeley and the
Lawrence Livermore National Laboratory. The team's results will be
published collectively until the end of this time period, after which
the particles will be made available to other members of the scientific
community.

"In science there's this unfortunate reputation of competition," Brennan
said. "People may ask: Why did Berkeley get the samples before us? But
in the end, we're trying to get the best science out there."

To this end, scientists have been developing methods to retrieve and
examine the particles since the project's launch. A major obstacle
confronted by the mission, according to Spencer, was figuring out how to
collect the samples slowly enough that they were not damaged. To
accomplish this, the collection plate on the shuttle was fitted out with
130 panels of a substance called aerogel.

Aerogel is a silica structure, like glass, that is 99.9 percent air,
making it the lowest density solid known to man, Spencer said. Due to
this, it has been dubbed "solid smoke." The low density of the aerogel
allowed the particles to be slowly captured by the shuttle.

"The comet moves at six times the speed of a rifle bullet," Spencer
said. "Usually you can't see the particles with the naked eye, so
scientists study the tracks and trails the dust leaves in aerogel. When
particles go through aerogel, they leave fragmentary debris."

Spencer will analyze this debris through two-step laser mass
spectrometry in order to find polycyclic aromatic hydrocarbons. She is
part of a team of scientists studying the organics of the particles
based on these fragments left in aerogel.

"We can get information out of stuff that would be trash to other
people," she said.

Brennan and his research partners, Konstantin Ignatyev, Katharina
Luening and Piero Pinanetta will map the elemental composition of the
particles using an X-ray microprobe at SLAC. According to Brennan, this
will help scientists begin to evaluate the process of star formation.

"This is a piece of unaltered pre-solar material," Brennan said. "Our
solar system coalesced out of pre-solar nebula 4.6 billion years ago.
Think about it: you have all this dust, and the lion's share becomes the
sun, the next biggest portion forms Jupiter, and the rest is left for
the other planets - but there's still some floating around, and it makes
comets. WILD-2 is one of those comets. This is an extremely important
step forward in potentially improving our understanding of how the solar
system was formed."

Brennan's team is slated to start research at the end of February;
analysis of the particles has already begun for some members of the
BayPac consortium.

"We are not going to have completely studied these particles by the end
of our allotted time," Brennan said. "We will be examining them for five
years minimum before we run of out tests to do on them. This is going to
be a treasure trove for years to come."
Received on Mon 06 Feb 2006 02:22:51 PM PST