This Galileo image of Prometheus is similar to the original Voyager picture.
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Io Discoveries with Voyager
When Voyager flew by Jupiter, no one thought that the moon, Io, would have volcanoes. However, there were three brave scientists who predicted that Voyager would find evidence that Io might be hot enough for volcanoes. The prediction was made just two weeks prior to the Voyager encounter with Io.
To everyone's surprise, when Voyager passed by, it actually caught the Prometheus geyser going off.
Later the three scientists who made the prediction were asked why they had taken the risk of making such a prediction, when they could easily have been wrong. They said that was what it meant to be a scientist.
The Galileo mission to Jupiter continues the exploration of the volcanism of Io.
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