Voyager 1 discovered volcanic activity on Jupiter’s moon Io.
During its 1979 flyby of Io, Voyager 1 returned images showing plumes rising from the moon’s surface. Imaging scientist Linda Morabito noticed one of the plumes while examining a spacecraft photograph. Additional images revealed several more, providing the first direct evidence of active volcanism beyond Earth.
Io is the most volcanically active world known in the Solar System. Its interior is heated by powerful tidal forces caused by Jupiter’s gravity and by orbital interactions with the moons Europa and Ganymede. These forces continually flex Io’s interior, generating heat that drives lava flows and sulfur-rich eruptions.
The discovery transformed scientists’ understanding of moons. Before Voyager, many researchers expected small, cold satellites to be geologically inactive. Io instead displayed mountains, lava-like features, colorful deposits, and a young surface with few impact craters. Voyager 2 also observed Io, but the first discovery of its volcanic plumes is specifically associated with Voyager 1.