What are some of the main differences between the Earth-like planets and the giant outer planets such as Jupiter and Saturn?
The planets in our solar system can be divided into two groups, the inner planets of Mars, Earth, Venus and Mercury and the outer, Jovian one of Jupiter, Saturn, Neptune, and Uranus. The inner planets are small and dense and contain substantial quantities of metals; their atmospheres contain oxygen, carbon dioxide and nitrogen. They are warmer than the outer ones due to their proximity to the sun and have shorter orbits. The outer planets are much larger and more massive but less dense, and lacking metals, and have atmospheres containing mainly hydrogen and helium.