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Cassini's closest encounter

NASA / JPL / SSI
The Cassini orbiter took this picture of the Saturnian moon Enceladus taken during Thursday's flyby.


The Cassini orbiter came through its closest-ever encounter with a Saturnian moon with flying colors - and with a fresh crop of cool black-and-white pictures of Enceladus. The most precious products of Thursday's 16-mile-high pass weren't the pictures, but the samplings of the mysterious stuff welling up from the cracks in Enceladus' icy surface.

"One of the key goals of this flyby seems to have been successful," Cassini project scientist Robert Pappalardo told me today.

The big reason why the 22-foot-high (6.8-meter-high) spacecraft came so close to Enceladus (25 kilometers, for the metrically inclined) was to collect samples of dust and other material given off by the moon.

Past flybys confirmed that water ice crystals and even organic molecules were emanating from geysers on the surface. During Thursday's encounter, scientists wanted to get closer-in samples, in hopes of pinpointing which materials were coming from where. Cassini's dust analyzer is tailor-made for such observations.

Due to a software glitch, "this particular instrument had a little bit of a hiccup the last time we tried to make this measurement," said Pappalardo, a planetary scientist at NASA's Jet Propulsion Laboratory. But the detector apparently worked like a charm this week.

"The spacecraft has detected individual peaks associated with the individual jets it flew over," Pappalardo said.

He compared the plume of ice and other materials to a hand reaching out from Enceladus itself. "Instead of seeing the 'fist,' we're seeing the fingers now," he said.

The dust analyzer should be able to tell scientists more precisely what's inside the jets of material given off by the geysers. It's tempting to think that the results could point to a "smoking gun" for life beneath Enceladus' surface - but that's a tall order. For now, Pappalardo is just happy to hear that Cassini has done its part.

"There is data in hand now," he said.

There are pictures in hand as well, and some of them have already been posted to the Cassini imaging team's Web site.

"The imaging team acquired fabulous images," Carolyn Porco of the Colorado-based Space Science Institute said in an e-mailed status report, "and the instruments designed to collect and measure the constituents of the plume for analysis did what they should."

In a follow-up phone call, Porco told me that close-up images weren't the primary objective for this week's flyby. The picture resolution was about 200 meters per pixel, compared with an ultra-sharp resolution of as little as 8 meters per pixel for the pictures taken during August's flyby.

Nevertheless, the raw black-and-white images provide another good look at the moon's cracked and craggy surface. And the next flyby, a 122-mile-high (197-kilometer-high) pass scheduled for Oct. 31, should serve up some tasty Halloween treats for Porco and her team.

"That one is designed for imaging," she said.