The Cassini spacecraft yesterday launched a probe on a three-week free-fall toward Saturn's mysterious moon Titan, where it will plunge into the hazy atmosphere and descend by...

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PASADENA, Calif. — The Cassini spacecraft yesterday launched a probe 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 instruments and cameras make observations.

The European Space Agency’s Huygens probe is equipped with instruments to sample the chemistry of Titan’s thick atmosphere, and may reveal whether the surface 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 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.

Huygens is scheduled to hit Titan’s atmosphere Jan. 14 and open a huge parachute that will allow it to make a 2½-hour descent while radioing findings 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.

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Cassini later will point its antenna at Earth and send the data.

Cassini is on a $3.3 billion mission to study Saturn, its spectacular rings and its dozens of 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 1½ times thicker than Earth’s. Titan has a surface temperature of minus-290 degrees.