[meteorite-list] NASA's Deep Impact Tells a Tale of the Comet

[Ron Baalke]

Dolores Beasley
Headquarters, Washington                        July 8, 2005
(Phone: 202/358-1753)

DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/393-9011)

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

RELEASE: 05-177

NASA'S DEEP IMPACT TELLS A TALE OF THE COMET

Data from Deep Impact's instruments indicate an immense 
cloud of fine powdery material was released when the probe 
slammed into the nucleus of comet Tempel 1 at 6.3 miles per 
second.

The cloud indicated the comet is covered in the powdery stuff. 
The Deep Impact science team continues to wade through 
gigabytes of data collected during the July 4 encounter with 
the 3-mile-wide by 7-mile-long comet.

"The major surprise was the opacity of the plume the impactor 
created and the light it gave off," said Deep Impact Principal 
Investigator Dr. Michael A'Hearn of the University of Maryland, 
College Park. "That suggests the dust excavated from the 
comet's surface was extremely fine, more like talcum powder 
than beach sand. And the surface is definitely not what most 
people think of when they think of comets -- an ice cube."

How can a comet hurtling through our solar system be made of a 
substance with less strength than snow or even talcum powder? 
"You have to think of it in the context of its environment," 
said Pete Schultz, Deep Impact scientist from Brown University, 
Providence, R.I. "This city-sized object is floating around in 
a vacuum. The only time it gets bothered is when the sun cooks 
it a little or someone slams an 820-pound wakeup call at it at 
23,000 miles per hour."

The data review process is not overlooking a single frame of 
approximately 4,500 images from the spacecraft's three imaging 
cameras taken during the encounter. "We are looking at 
everything from the last moments of the impactor to the final 
look-back images taken hours later, and everything in between," 
added A'Hearn. "Watching the last moments of the impactor's 
life is remarkable. We can pick up such fine surface detail 
that objects that are only four meters in diameter can be made 
out. That is nearly a factor of 10 better than any previous 
comet mission."

The final moments of the impactor's life are important, 
because they set the stage for all subsequent scientific 
findings. Knowing the location and angle the impactor 
slammed into the comet's surface is the best place to start. 
Engineers have established the impactor took two not unexpected 
coma particle hits prior to impact. The impacts slewed the 
spacecraft's camera for a few moments before the attitude 
control system could get it back on track. The penetrator hit 
at an approximately 25 degree oblique angle relative to the 
comet's surface. That's when the fireworks began.

The fireball of vaporized impactor and comet material shot 
skyward. It expanded rapidly above the impact site at 
approximately 3.1 miles per second, and the crater was just 
beginning to form. Scientists are still analyzing the data 
to determine the exact size of the crater. Scientists say 
the crater was at the large end of original expectations, 
which was from 50 to 250 meters. 

Expectations for Deep Impact's flyby spacecraft were exceeded 
during its close brush with the comet. The craft is more 
than 2.2 million miles from Tempel 1 and opening the distance 
at approximately 23,000 mph. The flyby spacecraft is 
undergoing a thorough checkout, and all systems appear to 
be in excellent operating condition.

The Deep Impact mission was implemented to provide a glimpse 
beneath the surface of a comet, where material from the solar 
system's formation remains relatively unchanged. Mission 
scientists hoped the project would answer basic questions 
about the formation of the solar system by providing an 
in-depth picture of the nature and composition of comets. 

The University of Maryland is responsible for overall Deep 
Impact mission science, and project management is handled by 
JPL. The spacecraft was built for NASA by Ball Aerospace & 
Technologies Corporation, Boulder, Colo. For information 
about Deep Impact on the Internet, visit:

http://www.nasa.gov/deepimpact

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

http://www.nasa.gov/home/index.html

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