Hubble Photo Gallery of Jupiter's Galilean Satellites
This is a Hubble telescope "family portrait" of Jupiter's four largest moons.
Located approximately a half billion miles away, the moons are so small that, in visible light, they appear as fuzzy disks in the largest ground-based telescopes. Hubble can resolve surface details seen previously only by the Voyager space probes in the early 1980s. While the Voyager probes provided close-up snapshots of the satellites, Hubble can now follow changes on the moons and reveal other characteristics at ultraviolet and near-infrared wavelengths.