Roe, Henry Lowell Observatory, Flagstaff, Arizona.
Lorenz, Ralph D. Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland.
Last reviewed:February 2019
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- History of observations
- Structure and composition
- Source of methane
- Seasons and time scales
- Clouds and circulation
- Huygens probe: Titan up close
- Related Primary Literature
- Additional Reading
The largest moon of Saturn and the only satellite in the solar system with a substantial atmosphere, as well as the only object, besides Earth, known to host stable bodies of liquid on its surface. Titan, 5150 km (3200 mi) in diameter, is the second largest natural satellite in the solar system, after Jupiter's Ganymede, and is larger than the planet Mercury. This large satellite's mass, 1.3452 x 1023 kg, is about two times that of the Moon, and has a lower mean density (1.9 g/cm3) than predominantly rocky, terrestrial worlds, indicating it contains a significant portion of icy and/or liquid material. Titan has an extended, dense atmosphere, mostly composed of nitrogen, that hides the surface in haze (Fig. 1). Given temperature and pressure conditions in this atmosphere, methane undergoes a meteorological cycle of evaporation and condensation, raining out of clouds, flowing as rivers, and pooling into lakes. The atmospheric chemistry and the solid surface on which liquids and aerosols can accumulate make Titan an attractive, natural, astrobiological laboratory for studying chemical evolution like that which ultimately led to life's emergence on the primitive Earth. See also: Astrobiology; Earth; Satellite (astronomy); Saturn; Solar system
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