Cassini Spacecraft to Fly Through Moon's Geyser

The Cassini spacecraft will perform its closest flyby ever of Saturn's ice-spewing moon Enceladus early next year, moving directly into its icy polar geyser for a deep-space shower.

Cassini's third flyby of Enceladus (en-SELL-ah-dus), set for March 2008, will swing it within 19 miles (30 kilometers) of the saturnian moon?almost six times closer than the spacecraft's closest pass to it in 2005. The tight trajectory will move Cassini directly into the icy geyser at the moon's southern pole, said NASA official James Green during a teleconference today.

"Cassini was never designed to fly this close, but we've just got to get in that plume and look at that material and see what it is and where it's coming from," said Green, director of NASA's Planetary Division in Washington, D.C.

Scientists think the geyser is 90 percent fine water-ice crystals, but suspect ammonia and methane gas are present as well.

Although the flyby isn't without risk, Alan Stern, associate administrator for NASA's Science Mission Directorate in Washington, D.C., said Cassini should fare well.

"It's very exciting because it's something Cassini wasn't designed to do but should be able to do safely," Stern said.

If the planned flyby is approved within a few months, Stern explained that the spacecraft's more delicate instruments will be pointed away from the icy spray before entering the plume, leaving particle analyzers to sniff out its composition.

Green said NASA's Jet Propulsion Laboratory is currently analyzing the geyser's risk to Cassini and will submit a formal assessment before the end of the year.
"We want to be able to safely do science [with Cassini], but push the limit," Green said.

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