A moon like no other: larger than some planets, Saturn's biggest moon indeed is a "Titan" of the solar system.

• Author: Braffman-Miller, Judith
• Position: Astronomy

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FAMOUS FOR ITS frozen methane clouds and hydrocarbon seas and lakes, Titan is a frigid, tortured moon that is mysterious, bizarre, and yet eerily like home--a remote, frozen time capsule that can tell us wonderful long-lost secrets about the way our Earth once was before fife emerged. It is a shadowy twilight world, shrouded in an enveloping hydrocarbon mist. This distant moon, the largest of Saturn, and the second largest in our solar system after Ganymede of Jupiter, sports a major continent, dubbed Xanadu by astronomers who were enchanted with the brightness of that region. Titan's Xanadu sparkles like a trillion rhinestones, and is soaked every morning by a relentless drizzle--not a watery spritzing like on Earth, but a persistent, bizarre drizzle of methane. The misty moisty mornings on Xanadu are blanketed by a dense orange fog.

Titan inhabits the realm of the outer solar system's giant planets--Jupiter, Saturn, Uranus, and Neptune. Like other bodies that reside far from the warmth of our sun, Titan is a frigid world, and the structure of its chemical atmosphere is frozen. It is this chemical composition that astronomers find so alluring, because Titan's atmosphere might be composed of a wonderful icy soup of compounds similar to those present in Earth's primordial atmosphere. Titan's dense cloudy atmosphere--denser than our own planers--primarily is nitrogen, like Earth's, but also contains much higher percentages of "smoggy" chemicals such as methane and ethane. The smog is so thick that it actually rains "gasoline-like" liquids down to the surface of the moon. Indeed, some scientists speculate that some of the chemicals discovered in Titan's atmosphere might indicate primitive methane-based life inhabits this truly incredible place.

Titan was discovered in 1655 by the Dutch astronomer Christiaan Huygens, and it is bigger than the planet Mercury. Indeed, it is almost as big as Mars, and it certainly would be classified as a planet if it circled the san instead of Saturn. Alas, the surface of Titan historically has been extremely difficult to explore--the dense smog of complex hydrocarbons that makes its atmosphere so intriguing likewise blocks an unimpeded view of its surface. Titan's atmosphere is very deep, composed of layers and layers of thick hazes that weave an intricate mesh of barriers that befuddle the sight of orbiting instruments.

In 1980, NASA'S Voyager 1 attempted to take close-up images of Titan's landscape, but was unable to pierce its dense cloud cover. Instead, the images revealed only inconsequential brightness and color deviations. Finally, in 1994, the venerable Hubble Space Telescope successfully obtained infrared images of Titan, which revealed the existence of Xanadu.

The Cassini-Huygens (CH) mission...