[meteorite-list] NASA's Deep Impact Adds Color to Unfolding Comet Picture

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Sep 6 15:23:10 2005
Message-ID: <200509061750.j86HoQH25580_at_zagami.jpl.nasa.gov>

Dolores Beasley
Headquarters, Washington
September 6, 2005
(Phone: 202/358-1753

Lee Tune
University of Maryland, College Park, Md.
(Phone: 301/405-4679)

RELEASE: 05-248

NASA'S DEEP IMPACT ADDS COLOR TO UNFOLDING COMET PICTURE

     Painting by the numbers is a good description of how
scientists create pictures of everything from atoms in our
bodies to asteroids and comets in our solar system.
Researchers involved in NASA's Deep Impact mission have been
doing this kind of work since the mission's July 4th
collision with comet Tempel 1.

"Prior to our Deep Impact experiment, scientists had a lot
of questions and untested ideas about the structure and
composition of the nucleus, or solid body of a comet, but we
had almost no real knowledge," said Deep Impact principal
investigator Michael A'Hearn, a professor of astronomy at
the University of Maryland, College Park, Md. "Our analysis
of data produced by Deep Impact is revealing a great deal,
much of it rather surprising."

For example, comet Tempel 1 has a very fluffy structure that
is weaker than a bank of powder snow. The fine dust of the
comet is held together by gravity. However, that gravity is
so weak, if you could stand on the bank and jump, you would
launch yourself into space.

Another surprise for A'Hearn and his colleagues was the
evidence of what appears to be impact craters on the surface
of the comet. Previously two other comets had their nuclei
closely observed, and neither showed evidence of impact
craters.

"The nucleus of Tempel 1 has distinct layers shown in
topographic relief ranging from very smooth areas to areas
with features that satisfy all the criteria for impact
craters, including varying size," A'Hearn said. "The problem
in stating with certainty that these are impact craters is
that we don't know of a mechanism by which some comets would
collide with the flotsam and jetsam in our solar system,
while others would not," he added.
According to A'Hearn, one of the more interesting findings
may be the huge increase in carbon-containing molecules
detected in spectral analysis of the ejection plume. This
finding indicates comets contain a substantial amount of
organic material, so they could have brought such material
to Earth early in the planet's history when strikes by
asteroids and meteors were common.

Another finding is the comet interior is well shielded from
the solar heating experienced by the surface of the comet
nucleus. Mission data indicates the nucleus of Tempel 1 is
extremely porous. Its porosity allows the surface of the
nucleus to heat up and cool down almost instantly in
response to sunlight. This suggests heat is not easily
conducted to the interior and the ice and other material
deep inside the nucleus may be pristine and unchanged from
the early days of the solar system, just as many scientists
had suggested.

"The infrared spectrometer gave us the first temperature map
of a comet, allowing us to measure the surface's thermal
inertia, or ability to conduct heat to the interior," said
Olivier Groussin, the University of Maryland research
scientist who generated the map.

It is this diligent and time consuming analysis of spectral
data that is providing much of the "color" with which Deep
Impact scientists are painting the first ever detailed
picture of a comet. For example, researchers recently saw
emission bands for water vaporized by the heat of the
impact, followed a few seconds later by absorption bands
from ice particles ejected from below the surface and not
melted or vaporized.

"In a couple of seconds the fast, hot moving plume
containing water vapor left the view of the spectrometer,
and we are suddenly seeing the excavation of sub-surface ice
and dust," said Deep Impact co-investigator Jessica
Sunshine, with Science Applications International
Corporation, Chantilly, Va. "It is the most dramatic
spectral change I've ever seen."

These findings were published in the September 9 issue of
the journal Science, and presented at the Division for
Planetary Sciences meeting in Cambridge, England. Mission
scientists are filling in important new portions of a
cometary picture that is still far from finished.

For more information about the Deep Impact mission on the
Internet, visit:

http://www.nasa.gov/deepimpact

For information about NASA and agency programs on the
Internet, visit:

http://www.nasa.gov/home

-end-
Received on Tue 06 Sep 2005 01:50:23 PM PDT