Crescent Titan viewed by Voyager 2 in August 1981 from ~200,000 kilometers.
The continuous ring is due to the presence of a thick atmosphere around Titan.
Sunlight is refracted or bent by the atmosphere along the edge of the disk, illuminating
the crescent. The bluish fringe is due to scattering by molecules in the atmosphere.
Titan is the largest major satellite of Saturn and the only
satellite in the solar system with a thick atmosphere. It is the second largest
satellite, with a diameter of 5150 kilometers. Although similar in bulk properties
to Ganymede and Callisto, Titan's thick
nitrogen and methane atmosphere clearly indicates that it is fundamentally different. The
atmospheric pressure at the surface of Titan is roughly 1.5 times as
high as that on the Earth. Some have proposed that a methane or ethane rain falls from the
skies of Titan, possibly forming lakes or oceans. Radar signals and HST images of the surface
suggest that these seas are not very extensive, but these observations are not yet conclusive.
Titan and Pluto are the last major unexplored planetary bodies in the solar system.
The Cassini Orbiter will make extensive
observations of Titan, Saturn, and its rings and satellites beginning in 2004.
[ Return to Satellites Page ]
This global view of Titan (Voyager 1) is nearly featureless due to a thick photochemical haze.
The haze is probably a byproduct of the breakdown of methane gas into hydrocarbons, and in
some sense resembles the infamous Los Angeles smog. This haze prevents us from seeing
Titan's surface and understanding its geologic history.
The Hidden Surface of Titan
Although Titan's thick haze is opaque at optical wavelengths, the atmosphere is more transparent
at infrared wavelengths. The Hubble Space Telescope looked at Titan in the infrared
and revealed the presence of dark and bright albedo regions. These markings could be
volcanic material, highlands washed by methane rain, or seas of ethane and hydrocarbons.
Despite these and other conjectures, the origins of these bright and dark markings are
simply not understood. The Huygens probe (on board Cassini launched in November 1997) will land
to the west of the large bright area. (Image courtesy of STScI.)
Titan images courtesy of NASA.
©Lunar and Planetary Institute, 1997
Supplemental Reading Materials
Beatty J. K., O'Leary B., and Chaikin A., eds. (1990) The New Solar System. Sky Publishing Corporation,
Cambridge, Massachusetts; Cambridge University Press, New York. 326 pp.