[meteorite-list] Unlocking the Frozen Secrets of Comet Wild 2

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 18 Dec 2006 14:34:11 -0800 (PST)
Message-ID: <200612182234.OAA07869_at_zagami.jpl.nasa.gov>

December 14, 2006

Contacts:
George Cody, g.cody at gl.ciw.edu
1-202-478-8980

Larry Nittler
lrn at dtm.ciw.edu
1-202-478-8460

Conel Alexander
alexander at dtm.ciw.edu
1-202-478-8478

Andrew Steele
a.steele at gl.ciw.edu
1-202-478-8974;

Marc Fries
m.fries at gl.ciw.edu
1-202-478-7970

PIO Source:
Tina McDowell
Carnegie Institution
1-202-939-1120
tmcdowell at pst.ciw.edu

Unlocking the frozen secrets of comet Wild 2

Washington, D.C. - Eleven months ago, NASA's Stardust mission touched down
in the Utah desert with the first solid comet samples ever retrieved from
space. Since then, nearly 200 scientists from around the globe have studied
the minuscule grains, looking for clues to the physical and chemical
history of our solar system. Although years of work remain to fully
decipher the secrets of comet Wild 2, researchers are sure that it
contains some of the most primitive and exotic chemical structures ever
studied in a laboratory.

Preliminary results appear in a special section of the December 15 issue of
Science. Overall, research efforts have focused on answering "big-picture"
questions regarding the nature of the comet samples that were returned,
including determining mineral structures, chemical composition, and the
chemistry of the organic, or carbon-containing, compounds they carry.
Carnegie researchers made key contributions to the latter effort. Out of
seven papers in total, four involved Carnegie scientists from the
Geophysical Laboratory (GL) and the Department of Terrestrial Magnetism
(DTM).

"Carnegie enjoys a unique concentration of instrumentation and expertise to
be able to engage in cutting-edge questions such as those posed by the
Stardust mission," said GL's Andrew Steele.

Scientists have believed that comets formed long ago in the cool outer
reaches of the solar system and thus largely consist of material that
formed at cold temperatures and escaped alteration in the blast furnace of
the inner solar nebula - the cloud of hot gases that condensed to form the
Sun and terrestrial planets some 4.5 billion years ago.

According to the record contained in the Stardust grains, it appears that
this hypothesis is about 90% right. Evidence from the ratios of certain
isotopes - variants of atoms that have the same chemical properties, yet
differ in weight - suggest that as much as 10% of the comet's material formed
in the hot inner solar nebula and was transported to the cold outer reaches
where the comet came together as the Sun formed. Chief among these
tell-tale isotopes are those of oxygen, for which the ratios resemble
those seen in meteorites known to have formed in the inner solar system.

Yet, isotopic measurements of hydrogen and nitrogen made at DTM and
elsewhere tell a different picture. "The presence of excesses of heavier
isotopes - deuterium and nitrogen 15, to be specific - is a strong indication
that some of the comet dust was around before the Sun formed," said DTM's
Larry Nittler. "It's really quite striking."

The structures of the comet's organic molecules tell a similar tale. "This
comet's organic material is really quite unusual compared to other
extraterrestrial sources we have studied, such as meteorites and
interstellar dust particles," said GL's George Cody. "Yet there are some
important similarities that tell that us we are not dealing with matter
that is totally foreign to our solar system."

The samples contain very few of the stable ringed, or aromatic, carbon
structures that are common on Earth and in meteorites. Instead, they have
many fragile carbon structures that would most likely not have survived the
harsh conditions in the solar nebula. These molecules also contain
considerably more oxygen and nitrogen than even the most primordial
examples retrieved from meteorites and exist in forms that are new to
meteorite studies.

"These forms of carbon don't look like what we find in meteorites, which is
something like compacted soot from your chimney. The carbon compounds from
this comet are a much more complicated mix of compounds," commented GL's
Marc Fries. "It will be an exciting challenge to explain how these
compounds formed and wound up in the comet."

"This leads us to our next big question," Cody remarked. "How could such
fragile material have survived capture at 6 km/sec collision velocity?"

"At this point, every question we answer raises several more questions,"
Nittler said. "But that is precisely what makes exploration so exciting and
makes sample return so important. We now have the samples to study for many
years to come."

Stardust, a project under NASA's Discovery Program of low-cost, highly
focused science missions, was built by Lockheed Martin Space Systems,
Denver, Colo., and is managed by the Jet Propulsion Laboratory, Pasadena,
Calif., NASA Science Mission Directorate, Washington, D.C. JPL is a
division of the California Institute of Technology in Pasadena. The
mission's principal investigator is Dr. Donald Brownlee
of the University of Washington in Seattle, WA. More information on the
Stardust mission is available at

http://Stardust.jpl.nasa.gov/home/index.html .

This work was supported by the National Aeronautics and Space
Administration (NASA),the NASA Astrobiology Institute, the National
Science Foundation (NSF), the U.S. Department of Energy (DOE), the
Particle Physics and Astronomy Research Council (PPARC), the Centre
National de la Recherche Scientifique (CNRS) and Centre National d'Etudes
Spatiales (CNES), France, the Universit? di Napoli, the Ministero
dell'Universit? e della Ricerca (MIUR), and the Istituto Nazionale di
Astrofisica (INAF), Italy.

The NASA Astrobiology Institute (NAI) was founded in 1997. It is a
partnership between NASA, 12 major U.S. teams, and six international
consortia. NAI's goal is to promote, conduct, and lead integrated
multidisciplinary astrobiology research and to train a new generation of
astrobiology researchers. For more information about the NAI on the
Internet, visit: http://nai.nasa.gov/

The Carnegie Institution of Washington
(http://www.carnegieinstitution.org/), a private nonprofit organization,
has been a pioneering force in basic scientific research since 1902. It has
six research departments: the Geophysical Laboratory and the Department of
Terrestrial Magnetism, both located in Washington, D.C.; The Observatories,
in Pasadena, California, and Chile; the Department of Plant Biology and the
Department of Global Ecology, in Stanford, California; and the Department
of Embryology, in Baltimore, Maryland.
Received on Mon 18 Dec 2006 05:34:11 PM PST