On Dec. 24, 2004, pyros blasted and the umbilical cord was cut as Cassini ejected the Huygens probe, sending it on a collision course with Saturn's largest moon. The spacecraft then turned and snapped a parting shot of the spinning probe. Still dormant and without navigation capabilities, the probe will travel the last 4 million kilometers (almost 2.5 million miles) on its own. Timers on board will wake Huygens up just before it enters Titan's hazy atmosphere.

Three days after the jettison, Cassini tweaked its trajectory to position itself at the necessary angle to capture data from Huygens. As Huygens reaches its destination and the probe's heat shield slams into Titan's atmosphere, Cassini will be flying some 72,000 kilometers (about 44,700 miles) from it. The spacecraft will then begin recording data collected by the six instruments on board the probe.

By the time Huygens has opened all three of its parachutes and gently landed on Titan, about 2 1/2 hours later, Cassini will be at a distance of 60,000 kilometers (about 37,300 miles). If the probe survives the landing, it will continue to gather data for up to 30 minutes. Soon after that, the mother ship will be off sight from the probe and transmission will end. Cassini will then turn its antenna toward Earth and send the data home. The probe will collect up to 400 million bits (about 500 MB) of data. The information will include images and sounds.

The Huygens mission is one of the most ambitious undertakings of the European Space Agency to date.

"The Huygens mission is the fruit of a lot of labor and commitments from many European nations, and its success will represent a moment in which all of Europe will be very proud of its achievements in space," says ESA's Dr. Claudio Sollazzo, Huygens mission operations manager. "But we could have only achieved that because we had a wonderful and very tight cooperation with NASA, in particular with the Cassini team at JPL."

Titan is expected to feature a multitude of liquid methane lakes. Accordingly, Huygens was built to float in the event it touches down on liquid. A splashdown would be gentler on the probe, raising the chances that Huygens could continue to collect data from the surface.

Landing on liquid should also make for good picture taking.

"The probe would then be able to measure the properties of these liquids, maybe sense the waves -- we know that Titan has very strong winds, so there maybe be waves on these lakes," says Sollazzo. "This would also bring some dynamics and nicer shots for our cameras at the end of the mission to show us that Titan could be a very interesting and fun place to be."