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

[Ron Baalke]

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

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