Space probe begins descent to Saturn moon

A European-designed space probe broke away from its NASA mothership on Friday on a plunge toward the mysterious Saturn moon Titan, starting a journey researchers hope will end with answers about one of the most puzzling bodies in the solar system.

Ground controllers received a signal at about 7.24 p.m. Pacific time (4.24 a.m. Malta time) indicating that Huygens had separated from NASA's Saturn probe Cassini, as small explosives sheared away locking bolts and a set of springs gently pushed the probe off on a collision course with Titan.

"The only thing we have to do now is assess how it left," said Earl Maize, deputy programme manager for the Jet Propulsion Laboratory here, referring to the probe's trajectory and how it spins as it heads to Titan. Huygens will now "sleep" for the next three weeks, coasting in a suspended state toward Titan and waking just four hours before its arrival on January 14.

The European Space Agency-managed Huygens aims to shed light on the only moon in the solar system with an atmosphere, a place where the surface may not be solid and the truth, scientists say, is almost certainly stranger than fiction.

"There are several books on the subject... and I'm sure that they're all wrong," said Jean-Pierre Lebreton, the Huygens project manager with the ESA.

Long a favorite home for science-fiction tales, Titan is larger than the planets Mercury and Pluto. Its atmosphere is mostly nitrogen, like Earth, but its surface temperatures of about -180°C make it inhospitable.

"In some sense it's a trip to early Earth," said David Southwood, director of the scientific programme for the ESA.

One of the biggest questions, Southwood and colleagues said, is whether there is any liquid on Titan's surface - like lakes filled with methane rain.

Huygens will hopefully answer that question, having already travelled 3.5 billion kilometres to Saturn over seven years on the hip of the NASA craft Cassini.

About 2.7 metres wide and shaped something like a flying saucer, it was due to make a leisurely descent of about two and a half hours through Titan's atmosphere, using three parachutes to reduce its speed and give the on-board instruments time to take detailed readings.

Once it reaches the surface of Titan, presuming there is a solid surface for it to impact, Huygens is expected to remain operational for only a brief time, possibly as little as 30 minutes, before its batteries die.

"It's fair to say we have very little idea what the surface is," Southwood said. "We don't know if we're going to splash down or crash down."