The four solar system gas giants share a number of features. All have atmospheres that are mostly hydrogen and helium and that blend into the liquid interior at pressures greater than the critical pressure, so that there is no clear boundary between atmosphere and body. They have very hot interiors, ranging from about 7,000 kelvins (K) for Uranus and Neptune to over 20,000 K for Jupiter. This great heat means that, beneath their atmospheres, the planets are most likely entirely liquid. Thus, when discussions refer to a "rocky core", one should not picture a ball of solid rock, or even, at 20,000 K, liquid rock. Rather, what is meant is a region in which the concentration of heavier elements such as iron and silicon is greater than that in the rest of the planet.
All four planets rotate relatively rapidly, which causes wind patterns to break up into east-west bands or stripes. These bands are prominent on Jupiter, muted on Saturn and Neptune, and barely detectable on Uranus. Uranus has an extreme tilt unlike the other gas giants that causes extreme seasons.
Finally, all four are accompanied by elaborate systems of rings and moons. Saturn's rings are the most spectacular, and were the only ones known before the 1970s. As of 2006, Jupiter is known to have the most moons, with sixty-three.
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