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European Probe On Its Way to Moon of Saturn

Craft to Descend Jan. 14

By William Harwood
Washington Post Staff Writer
Sunday, December 26, 2004; Page A03

CAPE CANAVERAL, Dec. 25 -- More than 750 million miles from Earth, the European Space Agency's Huygens probe was released from NASA's Cassini orbiter Christmas Eve and placed on a collision course with Titan, one of Saturn's many moons.

One of the most ambitious European space projects ever attempted, the flying saucer-shaped spacecraft -- named after Christiaan Huygens, the Dutch astronomer who discovered Titan in 1655 -- is scheduled to slam into the moon's thick atmosphere Jan. 14 at a blistering 12,400 mph.

Descending by parachute, a half-dozen powerful instruments aboard the compact, 700-pound Huygens will sniff out the constituents of smog-shrouded Titan's atmosphere, look for lightning, measure wind speeds and capture what promise to be spectacular vistas all the way down to the surface.

The long-awaited data will be transmitted to Cassini, which is flying past Titan about 37,300 miles away, stored on digital recorders and later relayed back to eager scientists on Earth.

"I feel very happy. We are now on our way to Titan," Jean-Pierre Lebreton, Huygens project scientist, said early Saturday after the craft's release from Cassini.

Huygens spent most of its seven-year voyage to Saturn in electronic hibernation, hitching a ride on Cassini. The NASA spacecraft braked into orbit around the ringed planet July 1 and made two flybys of Titan, in late October and earlier this month.

On Dec. 16, Cassini's main engine fired to put both spacecraft on a collision course with Titan. Just past 10 p.m. Eastern time Friday, powerful springs pushed Huygens away from its mothership, imparting a 7-rpm rotation for stability.

Flight controllers at the Jet Propulsion Laboratory in Pasadena, Calif., plan to fire Cassini's main engine again late Monday to steer the orbiter away from Titan and put it on the right course to capture the data from Huygens during the Jan. 14 descent.

Bigger than the planet Mercury, Titan is the only moon in the solar system with a thick atmosphere, one in which hydrocarbons presumably fall as rain and liquid ethane may pool on its ultra-cold surface.

When Cassini made its close flyby in late October, it beamed back pictures and radar data that revealed a strange, striated landscape with sharply defined bright and dark regions. But the atmosphere prevented the sort of clarity required to answer fundamental questions about the enigmatic moon.

"We've been saying for a long time now that Titan was the largest expanse of unexplored terrain in the solar system," imaging team leader Carolyn C. Porco said in October. "And what remains hidden under the atmosphere and under the haze [is] the solar system's last great mystery."


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