Its sheer size, although not known in antique times, is reason enough this planet is named after the father of the Roman gods: Almost 143 000 kilometers measures its diameter at the equator, about eleven times that of the Earth. The visible outer shell consists of gas, which is constantly in motion, forming bands of cloud with changing patterns and gigantic elliptical storms.

Jupiter is a system in its own right: Rocks and ice orbit the planet in a narrow ring and as numerous moons, of which the largest four measure several thousand kilometers in diameter. Galileo Galilei saw them through his telescope and deducted, that Earth could not be the center of the solar system, and they inspired Arthur C. Clarke to his famous novel 2001. They are worlds in their own right, with Io, the innermost of the large moons, showing abundant volcanic activity, and the surface of Europa covered by a thick layer of ice.