Io is Jupiter’s moon and the most volcanically active body in the solar system. Its surface contains hundreds of volcanoes, some of which erupt lava fountains and plumes hundreds of kilometers high.
Io’s extreme volcanism is caused by tidal heating. Jupiter’s enormous gravity constantly flexes the moon, while the gravitational pulls of Europa and Ganymede keep Io’s orbit slightly eccentric rather than perfectly circular. That repeated flexing generates heat inside Io, melting rock and driving widespread eruptions.
Io is slightly larger than Earth’s Moon, but its surface looks very different: lava flows and sulfur-rich deposits continually resurface it, erasing most impact craters. Voyager 1 revealed Io’s active volcanoes in 1979 when imaging scientist Linda Morabito identified a volcanic plume in a spacecraft photograph.
Europa and Enceladus are also important worlds for planetary science, especially because of their subsurface oceans. Triton shows signs of icy or “cryovolcanic” activity, but none matches Io’s intense, ongoing rock volcanism.