This 1981 Voyager-2 image shows the vast Saturn
ring system, as well as three small icy satellites and the shadow
of a fourth. Saturn is the second largest planet in the Solar
System. It has a volume about 760 times that of Earth. Like Jupiter,
Uranus, and Neptune, it has no solid surface, but is instead an
enormous sphere of gas which gradually compresses into fluid at
great depths beneath the clouds. Most of the visible markings
are formed in a layer of ammonia ice clouds, which form at a pressure
level in Saturn's atmosphere that is comparable to sea-level atmospheric
pressure on Earth. Above those clouds, Saturn's atmosphere, like
those of the Sun and the other three gas giant planets, is composed
almost exclusively of hydrogen and helium. By contrast, Saturn's
rings and icy satellites appear to be composed primarily of water
ice. Image reprocessed by USGS. (P-43538)
