September 6, 2005

Dolores Beasley
Headquarters, Washington 
(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 4 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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