Traveling space particles reveal secrets of comets
Donna Jones Pelkie
Argonne National Laboratory
March 10, 2006
ARGONNE, Ill. - They came from outer space.
And now, particles of comet dust that traveled from the far reaches of
the solar system to Earth are traveling the United States, including a
stop at the Advanced Photon Source at the U.S.
Department of Energy's Argonne National Laboratory. Scientists there
studying the particles to learn more about comets and possibly the
creation of our planet.
The particles are the first pieces of a comet to have ever been plucked
from outer space and returned to Earth. The collection was part of the
National Aeronautics and Space Administration's
(NASA) Stardust sample return mission which launched in February 1999.
The primary goal of Stardust was to collect dust and
carbon-based samples during its closest encounter with Comet Wild 2.
The Stardust sample-return canister parachuted onto the desert salt
flats of Utah on Jan. 15, following a journey of nearly three million
miles, bringing with it thousands of particles from the edge of the
Four of those samples recently spent a few days at Argonne, and almost
that entire time they were bombarded by the high-precision X-ray beams
from the Advanced Photon Source (APS). The samples are so small that
several particles fit across the width of a single human hair. By using
the APS to map the samples, researchers hope to determine their
makeup and to gain a better understanding of the composition of comets
and other planetary bodies, including the Earth. The studies were done
at GeoSoilEnviroCARS, a research facility at the APS operated by the
University of Chicago.
"Comets form far out in the solar system," explained researcher George
Flynn of State University of New York Plattsburgh who is working on the
project with Steve Sutton and Matt Newville of the University of
"They have trapped original parts of the solar system in ice for four
a half billion years. We have material that we think is the original
that the solar system formed from. And if we want to understand the
we need to understand what it's made of."
The particles were captured in aerogel, a special type of foamed glass,
made so lightweight that it is barely visible and almost floats in air.
Looking at the aerogel microscopically, Flynn said, it would resemble a
spider web. The particles travel through it, hitting individual strands
of the web, slowing with each impact, and eventually standing still,
embedded in the gel. The comet particles make carrot-shaped tunnels in
the aerogel as they are stopped. At the pointed tip of each tunnel, a
tiny particle will be found.
Researchers are analyzing the particles while they are still embedded
the aerogel. They use the APS to map the elements along the track left
by the comet particles. The aerogel is abrasive, and as the particles
travel through it, parts of them are scraped off and embedded in the
"If we just remove the particle and analyze only that," Flynn said, "it
might not be a true representation of the particle composition."
Researchers will map the elements along the path as well as the
particle, and "then we'll add them up and see what we get," Flynn said.
Flynn and his colleagues will also compare the data collected from
comet particles to data on particle samples that NASA routinely
from the Earth's upper atmosphere. Researchers have long believed that
some of those particles are, indeed, from comets, but without confirmed
comet samples to compare to, there's been no way to know for sure. This
project finally gives scientists the opportunity to determine the
characteristics of a comet. Flynn says researchers hope that if a comet
is sufficiently uniform, then by collecting such tiny pieces of it we
can understand a lot.
Prior to landing at Argonne, the samples were analyzed at the Advanced
Light Source at Lawrence Berkeley National Laboratory and the National
Synchrotron Light Source at Brookhaven National Laboratory.
Using the APS, the samples can be studied at much higher energies
allowing researchers to detect heavier elements and map the samples at
After the samples leave Argonne, Flynn said, they will be returned to
the Johnson Space Center in Houston where the particles will be
from the aerogel. Scientists there have the capability to extract
down to about 4 microns in size. Researchers will slice the particles
half and analyze them. Some of the particles will then make a return
to the APS where researchers will examine individual minerals in the
particles at the submicron scale.
Once all research is finished, the samples will be housed at the
Space Center and remain available for researchers around the world to
study. Sutton pointed out that's why non-destructive studies such as
this one are so valuable: The samples can be studied again in the
when even more refined methods become available.
Stardust is the first U.S. mission designed to return rock samples
the Apollo missions to the moon. " Nobody would have imagined back when
Apollo returned with the first space samples the types of studies that
would be possible today," Flynn said. "During the early years of space
exploration samples needed to be much larger, and measurements could
be done with the sensitivity that is available today."
The real benefit of sample return, Flynn points out, is that the
instruments used to study the material could not be taken into space.
"We could never send a synchrotron to the comet," he laughed.
Flynn and Sutton, who have been studying space particle samples
for nearly two decades, will present preliminary findings at NASA's
lunar and planetary science conference in March. They hope to have
studies complete in six months.