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In the early hours of July 4, Deep Impact's 820-pound "Impactor" collided with the Comet Tempel 1, providing scientists with a celestial show that should garner new insight into the evolution of comets. "You can not help but get a big flash when objects meet at 23,000 miles per hour," says Deep Impact investigator Pete Schultz of Brown University.
The resulting debris jet from the crash shot out from the comet's nucleus at 1,800 kilometers an hour. Pointing north-northeast, the jet was not uniform in color, suggesting that dust particles of varying sizes were moving at slightly different speeds. Instruments on board Impactor sent images back to NASA scientists up until three seconds before it intersected with the comet, with the final image taken from a distance of 18.6 miles. "From that close distance we can resolve features on the surface that are less than four meters across," explains principal investigator Michael A'Hearn of the University of Maryland, College Park. "When I signed on for this mission I wanted to get a close-up look at a comet but this is ridiculous¿in a great way."
Temperatures soared to several thousand kelvins in the wake of the crash, causing the disturbed debris to glow in the ultraviolet range. Although the comet contains a lot of ice, that is not what researchers are focusing on: "It's the other stuff deep inside we're most interested in--pristine material from the formation of the solar system locked safely below the comet's frozen surface," remarks Keith Mason of University College London. "We don't know exactly what we kicked up yet." Over the coming days, telescopes around the world, such as the La Silla Paranal Observatory in Chile, will continue to monitor the aftereffects of the collision, as will space-bound probes such as NASA's Swift telescope and the Deep Impact "Flyby" spacecraft from which the probe was launched.