The main difference between inner and outer planets is that outer planets are larger and are mainly made of gas. The inner planets are Venus, Mercury, Mars and Earth, while the outer planets are considered to be Saturn, Uranus, Neptune and Jupiter.
All of the inner planets are considered terrestrial planets due to the fact that their surfaces are made mostly of solids. These planets have no or few moons, with Earth having one moon, and Mars having two. In contrast, the outer planets are much more likely to have moons and rings. For example, Jupiter, known to be the largest planet in the solar system, has several moons.