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An artist's rendition of the Huygens probe separating from the Cassini spacecraft. Cassini is in the top-center part of the image; Saturn is to the right; Huygens is center-left; and the moon Titan, Huygens' target, is shown in the lower-left of the scene.
Click on image for full size
Image courtesy NASA.

Huygens probe on its way to Titan
News story originally written on December 30, 2004

NASA's Cassini spacecraft, which is in orbit around Saturn, released the Huygens probe and sent it on its way to Saturn's largest moon, Titan. The probe, pushed away from the Cassini "mothership" on December 24, 2004 by springs, will coast through space for three weeks before starting a 2-1/2 hour descent through Titan's atmosphere on January 14, 2005. Huygens will then land on Titan and may continue to send data for up to 30 minutes after it touches down on the icy moon.

Cassini and Huygens were launched from Cape Canaveral, Florida on October 15, 1997. The Huygens probe, riding "piggyback" on Cassini, has been in "sleep" mode throughout most of the seven-year journey to Saturn. Huygens doesn't have a rocket engine to steer itself, so the probe had to be aimed correctly for its approach to Titan when Cassini released it. Cassini fired its engines three days after releasing the probe to change its course and avoid following Huygens on its plunge into Titan's atmosphere. Cassini will continue to orbit Saturn, studying the gas giant planet and its rings and moons, for at least four years.

Huygens, built and operated by the European Space Agency and named after the 17th century Dutch astronomer Christiaan Huygens, will be "awakened" by an automatic timer 45 minutes before the start of its descent to Titan. The probe will gather data and images as it descends on parachutes through Titan's thick atmosphere. Huygens will send the data to Cassini, which will then relay the information to scientists on Earth. Huygens will follow a pre-programmed, automated routine during its descent, for Saturn is quite far from Earth and radio signals will take more than an hour to reach us from Cassini at the time of the probe's descent. Cassini will disappear over the horizon as viewed from the Huygens landing site about 30 minutes after the probe touches down, so we will lose contact with Huygens then unless its batteries wear out sooner.

Titan is the only moon in our Solar System with a thick atmosphere. Although Titan is quite cold, the conditions on the moon may be similar to those on Earth early in our planet's history. Scientists are especially interested in the complex chemistry of Titan's atmosphere, which includes many organic compounds and may shed light on Earth's early chemistry before life arose on our home planet. We aren't yet sure what Titan's surface is like, so although Huygens might touch down on solid ground it is also possible it will splash down in a lake or sea of liquid ethane or methane or it might plunge into a pile of frozen methane snow!

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