The Gas Giants
A Gas Giant is a large planet that is not predominantly composed of rocky material. The upper mass limit for gas giants is 8 times Jupiter's mass. Above this mass, the core will start to fuse hydrogen and the planet will ignite into a red dwarf.
The two types of gas giants that we know of are Jovian planets and Uranian planets. In our solar system, the Jovian planets are Jupiter and Saturn. These planets are mainly composed of metallic hydrogen (which forms at 4×10 6 bars of pressure; 1 bar = 0.987atm). They have a small rocky core and a thick atmosphere. The Uranian planets in our solar system are Uranus and Neptune. They are composed much more of ice and are sometimes called ice giants. They also have small rocky cores and thick atmospheres. In the outer solar system, rock refers to silicate material, ice refers to water, ammonia and carbon based compounds and gas refers to hydrogen and helium. Gas giants tend to oblate as they rotate which gives them a bulge in their equators. All the gas planets have bands of high velocity winds along the lines of latitude which blow in opposite directions to those opposite it. This is Belt-zone circulation.