Story updated 8:25 a.m. 12/25/04

PASADENA, Calif. (AP) -- A probe once attached to the international Cassini spacecraft was on its own Saturday for the first time, headed on a slow, tumbling course into the hazy atmosphere of Saturn's planet-size moon Titan.

The European Space Agency's Huygens probe carried instruments that may reveal more about the moon's chemistry and whether Titan actually has lakes or seas of liquid methane and ethane that have been theorized by scientists.

Cassini used springs to gently push the 705-pound probe away late Friday at a rate of one foot per second, sending it on a three-week free-fall toward Titan. Cassini will make a course change next week to avoid following the probe into the moon's atmosphere.

The probe's successful launch from Cassini put smiles on the faces of scientists in the control room at NASA's Jet Propulsion Laboratory in Pasadena.

"This was a big one partly because we had to do this right or no mission at all," said David Southwood, the European Space Agency's science program director.

A detailed analysis of the release was under way, but there were no indications of any problems, said Earl Maize, the Cassini deputy program manager at JPL. "We are quite confident we had a very clean release," he said.

Titan is the only moon in the solar system known to have a significant atmosphere. Rich with nitrogen and containing about 6 percent methane, the atmosphere is 1 1/2 times thicker than Earth's.

It also is a key target of Cassini's $3.3 billion mission to study the Saturn system, including the planet's spectacular rings and numerous moons. Scientists believe Titan may have organic compounds similar those that existed on the early Earth.

Designed for only a brief mission, the Huygens probe has no maneuvering system to adjust its own course and will remain dormant until just before hitting Titan's atmosphere on Jan. 14. It was named after 17th century Dutch astronomer Christiaan Huygens.

After plunging into the smog-like haze, it will deploy a huge parachute, allowing it to make a 2 1/2-hour descent while radioing findings back to Cassini. Scientists say the probe may continue sending data for up to 30 minutes, when either its battery fails or Cassini vanishes over Titan's horizon.

Cassini will later turn its antenna toward Earth and send the data back to NASA's Deep Space Network and on to an operations center in Darmstadt, Germany.

With the Saturn system averaging about 890 million miles from the sun, Titan has a surface temperature of minus 290 degrees Fahrenheit.

That surface continues to puzzle scientists despite close flybys in which Cassini's cameras have tried to peer through Titan's smog-like haze.

Imaging scientists have discerned distinct dark and light-colored areas, sometimes toying with such words as ''islands'' to describe features, but conceding they have yet to find a specific type of reflection that would indicate areas of liquid.

The Cassini spacecraft, launched in 1997, arrived at Saturn in June. The mission is a joint project of NASA, ESA and the Italian space agency.