The sixth planet from the Sun. Saturn is a gas giant, second only in size to Jupiter with a diameter more than 9 times that of Earth. It has a spectacular system of rings and a large collection of moons (23 currently known). Saturn also has the most flattened shape of any of the major planets. Its average density is so low that if placed in a big enough tub of water, it would easily float.  Saturn's atmosphere consists of 96.3% hydrogen and 3.25% helium, with traces of methane, ammonia, ethane, ethylene, and phosphine. Because Saturn is colder than Jupiter, the more colorful chemicals sink lower in its atmosphere and can't be seen. At Saturn's center is believed to lie a core of rocky material about the size of the Earth, but more dense. Around this is a metallic hydrogen shell some 30,000 km deep, surmounted, in turn, by a region composed of liquid hydrogen and helium with a gaseous atmosphere some 1,000 km deep.

(For further details see Saturn »)

(Source: The Internet Encyclopedia of Science »)