Solar System diagram. The planets of the Solar System are not shown to scale. The Sun is across bottom. At lower left, from left to right, are Mercury, Venus, Earth and Mars. These are known as the rocky, or terrestrial, planets. They are all made up of dense rock. Across upper frame, from left to right, are Jupiter, Saturn, Uranus and Neptune. These are the gas giant planets, made up of a small dense core surrounded by a thick atmosphere of gas. Across centre, the terrestrial planets are shown at the same scale as the gas giants. At lower right is a diagram of the orbits of the planets. At upper right is the Milky Way galaxy, which contains the Solar System.