Scientists marvel at comet collision

Alan Boyle Science editor • Profile • E-mail

A space probe's direct hit on a comet millions of miles from Earth drew oohs and ahs on Monday from astronomers, who said the celestial fireworks show could continue for weeks.

Hours after the Deep Impact mission’s refrigerator-sized Impactor probe collided with Comet Tempel 1, the Flyby mothership still spotted plumes of gas and dust flying out from the impact crater.

"If there are lots of volatiles there, the outgassing will continue to go on for some time ... [perhaps] a matter of weeks," principal scientific investigator Michael A'Hearn said Monday during a post-impact briefing at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

In the weeks and months ahead, scientists will be analyzing the results of the blast to learn more about the composition of comets — which could provide new insights on the formation of the solar system and perhaps even the origin of life on Earth. Findings from the $333 million Deep Impact mission could also help researchers devise strategies for diverting comets that might threaten Earth, said A'Hearn, a professor at the University of Maryland.

The collision, which occurred just before 2 a.m. ET Monday, was the climax of a six-month, 268 million-mile (429 million-kilometer) journey. It was a masterful feat of engineering: Twenty-four hours before the scheduled impact, the 820-pound (373-pound), copper-sheathed Impactor was released by the 1,325-pound (600-kilogram) Flyby craft into the comet's expected path.

Hit or miss?
At first, the autonomous Impactor was on a course that would miss the comet entirely, but it adjusted its trajectory to hit one of the brightest spots on the 3.7-mile-wide (6-kilometer-wide) comet while moving at a relative speed of 23,000 mph (37,000 kilometers per hour).

Deep Impact's mission team compared it to hitting one bullet with another bullet. "It looked a lot like one of our simulation runs," said mission navigator Shyam Bhaskaran.

Impactor’s imaging system sent back pictures of the potato-shaped comet right down to the last three seconds of its existence, while Flyby watched the impact from a front-row seat 5,000 miles (8,000 kilometers) away.

The initial impact came as a bright flash, and within seconds, sprays of ice and dust arced out from the crater. Flyby approached as close as a few hundred miles to analyze the debris, and kept gathering data and images even as it left Comet Tempel 1 behind, 83 million miles (133 million kilometers) from Earth.

The first images had mission team managers jumping and hooting for joy when they flashed on the big screens at the Jet Propulsion Laboratory's mission control. NASA quickly put the imagery on its Web site, attracting a billion hits — more than twice as many as were recorded on the busiest day of the twin-rover mission to Mars, said project manager Rick Grammier.

Andy Dantzler, NASA's solar system division director, pronounced Deep Impact a "smashing success."

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