Outer planets of the solar system are made predominantly of gases. They tend to have many more moons than the inner planets, and outer planets take a shorter period of time to rotate around their axes.
The outer planets are those past the asteroid belt, namely Jupiter, Saturn, Uranus and Neptune. They were formed at a greater distance from the sun, where the temperature was lower, than the inner planets. Metals and rocks condensed at higher temperatures closer to the sun to form the rocky planets, but the outer gas giants were formed by the condensation of gases such as helium and hydrogen and compounds of the latter. The gas giants are thought to have rocky cores surrounded by liquid hydrogen and helium.The strong gravitational fields of the outer planets stop atmospheric gases from escaping into space.
Jupiter, Saturn and Uranus have rings around them made of ice and dust. Scientists expect to discover rings around Neptune as well. The outer planets are massive enough to support their own moon systems. The outer planets have many moons because of their strong gravitational pulls, which supports the moons in their orbits, much like the sun supporting the planets in their orbits.
Gas giants rotate much faster than the inner planets. A day on Jupiter is roughly equal to 10 earth hours. This causes the gas giants to appear oblong instead of spherical.