Jupiter and Galilean satellites
Jupiter and its Galilean moons. Montage of images of Jupiter and its four largest satellites, known as the Galilean moons as they were discovered by the astronomer Galileo in 1610. The moons, in order of increasing orbital distance from Jupiter, are; Io (second right), Europa (centre), Ganymede (left) and Callisto (right). Jupiter has 16 known moons in four groups of four moons: the inner moons, the Galilean moons, the Himalia group and the Pasiphae group. The Galileans are by far the largest with diameters of 3000km to 5000km. The remainder range from 12 to 180km diameter. The images used in this montage were gathered by Voyager spacecraft in 1979.