NASA's Deep Impact Tells a Tale of the Comet
This false-color image shows comet Tempel 1 about 50 minutes after Deep Impact's probe smashed into its surface (back side of comet in this picture).
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July 08, 2005
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 about 10 kilometers per
second (6.3 miles per second or 23,000 miles per hour). 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 comet
measuring 5-kilometers-wide by 11-kilometers-long (about
3-miles-wide by 7-miles-long).
"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
Dr. 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 were 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 5 kilometers per
second (3.1 miles per second). 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 (165 to 820 feet) wide.
Expectations for Deep Impact's flyby spacecraft were exceeded during its
close brush with the comet. The craft is more than 3.5 million kilometers
(2.2 million miles) from Tempel 1 and opening the distance at approximately
37,000 kilometers per hour (23,000 miles per hour). 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.
JPL is a division of the California Institute of Technology, Pasadena, Calif.
For information about Deep Impact on the Internet, visit:
www.nasa.gov/deepimpact
DC Agle (818) 393-9011
Jet Propulsion Laboratory, Pasadena, Calif.
Dolores Beasley (202) 358-1753
NASA Headquarters, Washington
Lee Tune (301) 405-4679
University of Maryland, College Park
2005-113
