Source: Voyager 1

Information: Jupiter and its four planet-size moons, called the Galilean satellites, were photographed in early March by Voyager 1 and assembled into this collage. They are not to scale but are in their relative positions. Reddish Io (upper left) is nearest Jupiter; then Europa (center), Ganymede and Callisto (lower right). Not visible is Jupiter's faint ring of particles, seen for the first time by Voyager 1.