PASADENA, Calif. – The Cassini spacecraft (search) launched a probe Friday on a three-week free-fall toward Saturn's mysterious moon Titan, where it will plunge into the hazy atmosphere and descend by parachute while its science instruments and cameras make observations.
The European Space Agency's Huygens probe (search) is equipped with instruments to sample the chemistry of Titan's thick atmosphere, and may reveal whether the surface actually has lakes or seas of liquid methane and ethane that have been theorized by scientists.
A signal confirming release of the probe was received at NASA's Jet Propulsion Laboratory (search) at 7:24 p.m. PST. The actual event occurred earlier, but it took more than an hour for radio signals to cross the hundreds of millions of miles between Saturn and Earth.
Smiles broke out in the JPL control room where many members of the mission staff wore red and white Santa hats.
"This was an amicable separation after seven years of living together," ESA science program director David Southwood said in a statement. "Each spacecraft will now continue on its own, but we expect they'll keep in touch to complete this amazing mission."
Huygens is scheduled to hit Titan's atmosphere on Jan. 14 and open a huge parachute that will allow it to make a 21/2-hour descent while radioing findings back to the mother ship. After touching down at 15 mph, it 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 home.
Cassini was equipped with springs to gently push the 705-pound probe away at a rate of one foot per second and impart a stabilizing spin of seven revolutions per minute. The aim had to be good because Huygens has no maneuvering system to adjust its own course.
Cassini is on a $3.3 billion mission to study Saturn, its spectacular rings and its numerous moons, situated an average of about 890 million miles from the sun. Scientists believe Titan may have organic — meaning carbon-based — compounds similar those that existed on the early Earth.
Bigger than the planets Mercury and Pluto, 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 11/2 times thicker than Earth's. Titan has a surface temperature of minus 290 degrees.
Its surface puzzles scientists, despite close flybys in which Cassini's cameras have tried to peer through Titan's haze. Scientists have discerned distinct dark and light areas, sometimes toying with such words as "islands" to describe features, but conceding they have yet to find a certain type of reflection that would indicate liquid.
The Cassini mission is a joint project of NASA and the European and Italian space agencies. Cassini was launched from Cape Canaveral, Fla., in 1997 and arrived at Saturn in June.