[meteorite-list] Scientists Begin Intense Study of Stardust Particles
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Feb 1 15:38:11 2006
Scientists Begin Intense Study of Stardust Particles
By Amir Alexander
The Planetary Society
31 January 2006
As scientists in building 31 at the Johnson Space Center are working to
extract particles from Stardust's aerogel collectors, work is already
beginning on analyzing the pristine grains the spacecraft brought to Earth.
In particular, it has been a very busy weekend for Stardust_at_home
leader Andrew Westphal and other members of the Stardust team gathered at
the University of California in Berkeley. For 10 days following the
successful landing of Stardust's sample return capsule on January 15,
Westphal had been ensconced in the Johnson Space Center in Houston,
taking part in the opening of the capsule and the first examinations of
the samples it brought to Earth. Then, on January 26, he headed home to
Berkeley. In his carry-on luggage for his flight, he took with him what
can only be described as a priceless treasure: one half of an aerogel
tile from Stardust, containing samples from comet Wild 2.
Once back on the California campus, Westphal and his colleagues quickly
went to work. Their tool was the Advanced Light Source (ALS) synchrotron
in the Lawrence Berkeley Laboratory, in the hills above the Bay Area
campus. "A synchrotron," explained Westphal, "is an instrument the size
of a shopping mall." A near-circular tube runs around the premises,
inside of which sub-atomic particles are accelerated to phenomenal
speeds. Powerful magnets, placed at pinpoint precision around the
circular tube make sure that the particles stay on track and keep in
motion for hours at a time.
The real action, said Westphal, occurs right around these magnets, where
the synchrotron emits an extremely intense white light radiation. This
covers the spectrum all the way from infrared to ultraviolet. Because
the radiation is so strong, scientists can parse it to the precise
frequency that they need and still get a clear and powerful signal.
Using synchrotron, the station at magnet number 10, Westphal and his
collaborators Matthew Marcus of U.C. Berkeley, George Flynn of SUNY
Plattsburgh, Zack Gainsforth of U.C. Berkeley, and Sean Brennan of
Stanford, exposed their half tile of aerogel to a succession of trials.
In the first, they tuned the beam to the "K-edge of iron," meaning it
was at the precise frequency that would just barely dislodge an electron
from the "K" shell of an atom of iron. When the electron is released,
the particle glows in the X-ray range, and the precise spectra and their
relative strength tell scientists a great deal about the elements present.
The Stardust team then analyzed their sample using XANES, which stands
for X-ray Analysis Near-Edge Spectroscopy. In this method, the sample is
scanned at a tight range of frequencies, from just below to just above
the K-edge of iron. This test can reveal the state of the different
elements in the sample with great precision. Finally they subjects the
sample to an intense beam for an X-ray diffraction analysis. This test
is similar to X-ray crystallography, where researchers use X-ray images
to detect the internal structure of a sample.
Westphal and his colleagues spent Friday and the entire weekend at the
ALS synchrotron, running and re-running their tests. Finally, after 3
intense days of work, they got a break on Monday to relax and begin
pondering their experiments. It is far too early to announce any
results, explained Westphal. These will have to wait until the data is
carefully analyzed and interpreted, which will take time. Nevertheless,
one thing is clear: after years of waiting for the arrival of Stardust's
pristine particles, scientists are wasting no time in beginning the
intense analysis of these precious samples from space.
Received on Wed 01 Feb 2006 02:12:05 PM PST