Why are the outer four planets sometimes called gas giants? They are made of mostly ice and do not have a rocky surface.
They have atmospheres of gas and the inner planets do not.
They are made of gas and are much larger than the terrestrial planets.
They orbit the earth in a different direction than the inner planets.

These planets are much larger than the inner planets and are made primarily of gases and liquids, so they are also called gas giants. ... Since the inner planets didn't have enough mass to hold on to these light gases, their hydrogen and helium floated away into space.

Explanation:

The planets of the solar system as depicted by a NASA computer illustration. A gas giant is a large planet composed mostly of gases, such as hydrogen and helium, with a relatively small rocky core. ... The gas giants of our solar system are Jupiter, Saturn, Uranus and Neptune

Explanation: