Analyzing photographs taken by Voyager 1 during its Jupiter flyby, navigation engineer Linda Morabito noticed a strange crescent-shaped feature jutting off the edge of Io. It turned out to be a plume of volcanic material blasting roughly 300 kilometers into space, proof that Io was geologically alive—the first direct evidence of active volcanism found anywhere beyond Earth.
Voyager 1 had already swept past Jupiter and its moons by early February 1979, but the mission's scientists were still combing through the spacecraft's thousands of images for anything unusual. On February 19, JPL engineer Linda Morabito was using an image of Io to help pinpoint the spacecraft's exact position among the star fields when she noticed an odd bump protruding from the moon's limb, too large and oddly shaped to be a background star or a common camera artifact.
Further analysis confirmed it was a plume of gas and dust erupting from Io's surface and arcing hundreds of kilometers above it, powered by intense volcanic activity driven by tidal heating from Jupiter's gravity. It was the first time humans had directly observed active volcanism on a world other than Earth, later revealed to be one of at least nine such plumes erupting simultaneously across Io's sulfur-streaked surface.
The discovery transformed Io from a minor curiosity into one of the most geologically dynamic bodies in the solar system, and it validated a prediction made just days earlier by a team of scientists who calculated that tidal flexing from Jupiter's gravity should generate enough internal heat to melt Io's interior. Io remains the most volcanically active body known in the solar system.
Key people: Linda Morabito