NASA craft snaps pics of comet in Valentine fling

NASA craft snaps pics of comet in Valentine fling
PASADENA, Calif. – Nearly six years after an 800-pound copper bullet excavated a crater on a comet, a NASA spacecraft revisiting the site has seen evidence of the destruction in images snapped during a Valentine's Day flyby, scientists said Tuesday.

Instead of a well-defined pit, the Stardust craft saw what looked like a crater rim that was filled in the middle — a sign that the plume of debris from the 2005 high-speed crash that created the crater shot up and fell back down.

"The crater was more subdued than I think some of us thought," said mission scientist Pete Schultz of Brown University. "It partially buried itself."

Stardust zoomed past Tempel 1 Monday night, passing within 110 miles of the comet's surface. Along the way, it snapped six dozen pictures.

It was NASA's second visit to Tempel 1, but the first time a spacecraft had imaged the manmade crater.

In 2005, another NASA probe, Deep Impact, fired a projectile into Tempel 1 that carved a football-sized hole, but so much dust spewed out that it blocked Deep Impact's view.

Astronomer Michael A'Hearn of the University of Maryland, who led Deep Impact, was pleased to come full circle.

"It's wonderful to go back and see the effects we had on the comet due to our impact," A'Hearn said.

Revisiting with Tempel 1 also allowed scientists to examine changes on the surface since Deep Impact.

Tempel 1 has since made a full loop around the sun. Every time comets orbit the sun, they lose material from the surface and become less bright.

Scientists found evidence of erosion in then-and-now images of the Deep Impact site, said principal investigator Joe Veverka of Cornell University.

Stardust continued beaming back images from the Valentine encounter Tuesday. Scientists planned to spend the next several weeks analyzing the data.

Stardust's trip to Tempel 1 was a bonus mission. Launched in 1999, Stardust's original target was comet Wild 2, where it collected dust samples that were later jettisoned to Earth.

The Tempel 1 flyby went off almost flawlessly. Stardust got knocked several times by dust grains, but its protective bumpers bore the brunt of the blast and it came out unharmed.

A slight problem occurred during download. Since Stardust's antenna was pointed away from Earth during the flyby, it stored all the images and data in its memory, waiting to be played back at a later time.

NASA's plan was to downlink close-up pictures to the ground first, followed by shots farther away. For reasons that engineers are still troubleshooting, the pictures came down in the order they were taken with the most distant views popping up first.

Normally, it wouldn't be a big deal. But since Stardust's camera is a spare from the Voyager program, it takes a long time for each image to be received.

The glacial download disappointed some space fans who stayed up on Valentine's night for a glimpse of the comet nucleus. After NASA announced that the closest approach images won't be ready until Tuesday, scores of people on Twitter, Facebook and other social networking sites signed off.