Largest Moon of Saturn - Titan (21st Moon outwards from Saturn)

Discovery

Titan was discovered in 1655 by Christiaan Huygens using a 57-millimeter objective lens on a refracting telescope of his own design.

Naming

The name Titan, and the names of all seven satellites of Saturn then known, come from John Herschel (son of William Herschel, discoverer of Mimas and Enceladus) in his 1847 publication Results of Astronomical Observations Made at the Cape of Good Hope. He suggested the names of the mythological Titans, sisters and brothers of Kronos, the Greek Saturn.

Stats

Titan is frequently described as a planet-like moon. Titan has a diameter roughly 50% larger than Earth's moon and is 80% more massive. It is the second-largest moon in the Solar System, after Jupiter's moon Ganymede, and it is larger by volume than the smallest planet, Mercury.

Diameter: 5,151 km

Semi-major axis: 1,221,930 km

Orbital Period: 15.95 days

Orbit

Titan takes as long to rotate on its axis as it does to make one orbit of Saturn; and therefore always keeps the same hemisphere pointed to Saturn.

Composition

Titan is primarily composed of water ice and rocky material. Much as with Venus prior to the Space Age, the dense, opaque atmosphere prevented understanding of Titan's surface until new information accumulated with the arrival of the Cassini–Huygens mission in 2004.

This includes the discovery of liquid hydrocarbon lakes in the satellite's polar regions. These are the only large, stable bodies of surface liquid known to exist anywhere other than Earth. The surface is geologically young; although mountains and several possible cryovolcanoes have been discovered, it is smooth and few impact craters have been discovered.

Atmosphere

The atmosphere of Titan is largely composed of nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog. The climate — including wind and rain — creates surface features similar to those of Earth, such as sand dunes, rivers, lakes and seas (probably of liquid methane or ethane) and shorelines, and, like on Earth, is dominated by seasonal weather patterns.

Life?

With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan is viewed as analogous to the early Earth, although at a much lower temperature.

The satellite has thus been cited as a possible host for microbial extraterrestrial life or, at least, as a prebiotic environment rich in complex organic chemistry. Researchers have suggested a possible underground liquid ocean might serve as a biotic environment.

It has also been suggested that a form of life may exist on the surface, using liquid methane as a medium instead of water; and anomalies in atmospheric composition have been reported which are consistent with the presence of such a life-form, but which could also be due to an exotic non-living chemistry.