Titan (or Saturn VI) is the largest moon of Saturn. It is the only moon in our solar system known to have a dense atmosphere, and the only object other than Earth that has visible liquid on its surface.
Titan is the sixth moon from Saturn. Frequently described as a planet-like moon, Titan has a diameter roughly 50% larger than the Moon and is 80% more massive. It is the second-largest moon in the Solar System, after Jupiter's moon Ganymede, and is larger by volume than the smallest planet, Mercury, although only about 41% as massive. Titan is 3,200 miles across (5,150 km), compared to 3,031 miles for the planet Mercury (4,879 km) , and 2,159 miles for the Moon (3,474 km) , and 12,742 km for the Earth.
In the photo below Titan is on the lower left; the moon is in the upper left.
Titan was the first known moon of Saturn, discovered in 1655 by the Dutch astronomer Christiaan Huygens, and was the fifth moon of a planet apart from the Earth to be discovered.
Titan is likely differentiated into several layers with a 2,113 mile wide rocky center (3,400 km) surrounded by several layers composed of different crystal forms of ice. Its interior may still be hot and there may be a liquid layer consisting of a "magma" composed of water and ammonia between the different layers of ice. The presence of ammonia allows water to remain liquid even at temperatures as low as 176 K.
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, including the discovery of liquid hydrocarbon lakes in the satellite's polar regions. The surface is geologically young; although mountains and several possible cryovolcanoes have been discovered, it is smooth and few impact craters have been found.
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 dunes, rivers, lakes and seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids (both surface and subsurface) and robust nitrogen atmosphere, Titan's methane cycle is viewed as being similar to Earth's water cycle, although at a much lower temperature
The natural color composite above was taken during the Cassini spacecraft's April 16, 2005, flyby of Titan. It is a combination of images taken through three filters that are sensitive to red, green and violet light. It shows approximately what Titan would look like to the human eye: a hazy orange globe surrounded by a tenuous, bluish haze. The orange color is due to the hydrocarbon particles which make up Titan's atmospheric haze. North on Titan is up and tilted 30 degrees to the right.
A black and white image of Titan is below.