Voyager 1 was the first spacecraft to detect volcanic plumes on Jupiter’s moon Io.
During its 1979 encounter with the Jupiter system, Voyager 1 photographed Io’s strange, colorful surface. On March 8, navigation engineer Linda Morabito noticed a cloud rising from Io’s limb in an image taken for optical navigation. The feature was identified as a volcanic plume about 300 kilometers high, later associated with the volcano Pele.
Analysis of additional Voyager 1 images revealed nine plumes scattered across Io. The discovery provided the first direct evidence of active volcanism beyond Earth. Voyager 1 also detected thermal emissions and material associated with Io’s volcanic environment, strengthening the interpretation.
Voyager 2 flew past Io four months later and observed changes in plume deposits, but it was not the first to detect them. Galileo later monitored Io extensively, while New Horizons observed the moon during its 2007 Jupiter flyby. Io’s intense volcanism is powered largely by tidal heating caused by gravitational interactions with Jupiter, Europa, and Ganymede.