Jupiter’s moon covered by active volcanoes is Io. It is the most volcanically active world in the Solar System, with hundreds of volcanoes that erupt lava and send plumes of sulfur and sulfur dioxide into space.
Io’s intense volcanism is caused by tidal heating. Jupiter’s enormous gravity continually stretches and compresses the moon, while gravitational interactions with Europa and Ganymede keep Io’s orbit slightly eccentric. The resulting friction heats Io’s interior enough to melt rock and drive widespread eruptions.
The moon’s volcanic nature was confirmed in 1979, when NASA’s Voyager 1 spacecraft photographed volcanic plumes rising above Io’s surface. Some eruptions produce lava fountains dozens of miles high, and fresh flows constantly resurface the moon, leaving relatively few impact craters.
Io is sometimes confused with Europa, another major moon of Jupiter. Europa is famous for its icy shell and suspected subsurface ocean, while Io is the fiery, sulfur-colored moon dominated by active volcanoes. Its name comes from Io, a priestess in Greek mythology who was associated with Jupiter, the Roman counterpart of Zeus.