the fifteenth and largest of Saturn's moons

Titan has a diameter of 3,200 miles (5,150 kilometers), and orbits Saturn at a distance of 758,756 miles (1,221,830 kilometers). It was discovered by Christiaan Huygens in 1655. In Greek mythology the Titans were a family of giants, the children of Uranus and Gaia, who sought to rule the heavens but were overthrown and supplanted by the family of Zeus.

Titan has been "visited" by three probes. One of the principal objectives of the Voyager I mission was the study of Titan. Coming within 2,500 miles of the surface, Voyager I provided more information about Titan in the span of just a few minutes than had been accumulated over the past 300 years. In late-2004, the Cassini probe made a series of close encounters with Titan and took a variety of measurements. In January 2005, the Huygens probe actually landed on the surface of Titan.

Titan is similar in composition to Ganymede, Callisto, Triton, and (probably) Pluto, being about half water ice and half rocky material. It may have a rocky center surrounded by several layers composed of different crystal forms of ice, and may have an interior that is still hot.

Unlike almost every other satellite in the Solar System, Titan has a significant atmosphere. It is composed primarily of molecular nitrogen, with no more than 6% argon and a small amount of methane. There are also trace amounts of at least a dozen other organic compounds -- including ethane, hydrogen cyanide and carbon dioxide -- and water. The atmosphere is actually so thick that for centuries it was thought that Titan was actually larger than Ganymede. At the surface, the pressure is 50% higher than Earth's.

At the surface, Titan's temperature is about -290° F. At this temperature water ice does not sublimate, meaning there is little wapor vapor in the atmosphere. But there are clouds in that atmosphere, most likely composed of methane, ethane, or other simple organics. Pictures of Titan's surface indicate that those clouds may actually produce enough "rain" to create rivers and lakes. In addition, Cassini found evidence of a "volcano" which may be responsible for replenishing Titan's atmosphere.

Saturn
Christiaan Huygens
Triton
Pluto

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