Scientists marvel at comet collision

The science of comets
Comets are "dirty snowballs" that are thought to represent leftovers from the creation of the solar system. Because comets were born in the system’s outer fringes, their cores still possess some of the primordial ingredients, and studying them could yield clues to how the solar system formed 4.5 billion years ago.

Scientists are just beginning to analyze the imagery and spectral data from the Flyby mothership, which should tell them the chemical composition of Comet Tempel 1's interior.

Brown University's Pete Schultz, a member of the Deep Impact science team, said that scientists didn't expect the outgassing to continue as long as it has, based on the simulations conducted before impact. "Now we have to go back to the drawing board and do some more complicated scenarios," he said.

Based on a preliminary analysis, Schultz speculated that the Impactor probe plowed through a soft, dusty surface, then hit a subsurface layer of ice with enough energy to vaporize the ice as well as the probe itself.

No danger to Earth
Collisions with objects such as comets and asteroids are thought to have sparked mass extinctions on Earth in the ancient past, including the disappearance of the dinosaurs. Scientists emphasized that Comet Tempel 1 poses no threat to Earth — and that the Impactor blast, though spectacular, had essentially no effect on the comet's course. However, A'Hearn said the mission could represent one small step toward heading off a catastrophic cometary collision if and when the time came.

"The knowledge that comes out of this … is important to understanding how to deflect a comet," he told reporters.

A'Hearn said he was intrigued by the apparent craters that showed up in the last imagery from Impactor. Scientists have seen the surfaces of comet nuclei before — such as Comet Borrelly and Comet Wild 2 — but "this is the first time we've seen things on the surface that look like impact craters to many of us," A'Hearn said.

Deep Impact's blast was itself expected to create a crater ranging anywhere from the size of a large house to a football stadium and be between two and 14 stories deep. The Planetary Society sponsored a guessing game on the crater’s size — and some members of the science team had even put money down in an office pool. Schultz said he would bet that the crater was bigger than a house, but A'Hearn said it was still too early to determine the size.

"It probably means anybody’s pool can't be paid off for another week," he said.

This report includes information from The Associated Press.

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