Volume: 03, Issue: 14 07/13/2005 
This spectacular image of comet Tempel 1 was taken 67 seconds after it obliterated Deep Impact's impactor spacecraft. Image courtesy NASA/JPL-Caltech/UMD.
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This false-color image shows comet Tempel 1 about 50 minutes after Deep Impact's probe smashed into its surface. Image courtesy NASA/JPL-Caltech/UMD.
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This image shows comet Tempel 1 approximately 5 minutes before Deep Impact's probe smashed into its surface. Image courtesy NASA/JPL-Caltech/UMD.
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Other Articles in This Issue:
First Discovery Launch Attempt Scrubbed
Spongy-Looking Hyperion Tumbles into View
Satellites Examine Sea Level Changes
Take Advantage of Summer Opportunities
 

Deep Impact Completes Spectacular Mission

The hyper-speed demise of NASA's Deep Impact probe is uncovering countless secrets about the life of a comet. Deep Impact scientists theorize the 820-pound impactor vaporized deep below the comet's surface when the two collided at 1:52 a.m. July 4, at a speed of 6.3 miles per second.

"They say a picture can speak a thousand words," said Deep Impact project manager Rick Grammier of NASA's Jet Propulsion Laboratory. "But when you take a look at some of the ones we captured in the early morning hours of July 4, 2005, I think you can write a whole encyclopedia."

Preliminary assessment of images and data from Deep Impact and the flyby craft have provided the closest glimpse of a comet that scientists have ever seen. Data from Deep Impact's instruments indicate an immense cloud of fine powdery material was released when the probe slammed into the nucleus of Tempel 1 at about 23,000 miles per hour. The cloud indicated the comet is covered in the powdery stuff.

"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. "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. "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," A'Hearn said. "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 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 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 2.2 million miles from Tempel 1 and opening the distance at approximately 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.

For information about Deep Impact on the Internet, visit www.nasa.gov/deepimpact .

    
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