Titan is the largest moon of Saturn and the second-largest in the Solar System. It is the only moon known to have an atmosphere denser than the Earth's and is the only known object in space—other than Earth—on which there is clear evidence that stable bodies of liquid exist.

Titan is primarily composed of ice and rocky material, with a rocky core surrounded by various layers of ice, including a subsurface layer of ammonia-rich liquid water.

The atmosphere of Titan is mainly nitrogen and methane; minor components lead to the formation of hydrocarbon clouds and heavy organonitrogen haze. Its climate—including wind and rain—creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas (probably of liquid methane and ethane), and deltas, and is dominated by seasonal weather patterns as on Earth.