Solar system planets. Computer illustration showing the nine planets of our solar system. The planets are not drawn to scale. Here, the gas giant planets are at left, with the rocky planets at right. At bottom, Jupiter (left) merges with Earth (right). Above Jupiter, from bottom to top, are Saturn, Neptune and Uranus. Above Earth are Mars, Venus and Mercury. At centre are Pluto and its moon Charon, which are thought to have rocky cores, but little else is known. The gas giants are made almost entirely of hydrogen and helium, while the rocky planets have a much higher proportion of heavy elements such as iron, silicon and oxygen.