Jupiter's interior. Cutaway computer illustration showing the interior structure of the planet Jupiter. Jupiter is the fifth planet from the Sun and the largest in the solar system, with a mass two and a half times that of all the other planets put together. A rocky core (grey, centre) about the size of Earth lies at its centre, where the temperature is 20,000-30,000 degrees Celsius. Around the core is a vast layer of liquid hydrogen, which accounts for most of the planet's mass. The inner part of the hydrogen layer is under such high pressure that it acts like molten metal. The outermost parts of the planet consist of a thin atmosphere of hydrogen, water and ice, ammonium hydrosulphide and ammonia crystals.Henning Dalhoff / Science Photo Library