Io, a moon of Jupiter. The Voyager 2 spacecraft flew past Jupiter and its moons in early July, about 4 months after the Voyager 1 encounter. Voyager 1 imagery showed active volcanism on lo, the first extraterrestrial body on which volcanic eruptions have been observed.
Voyager 2's cameras viewed lo intermittently for 5 days, including continuous imaging for about 7 hours around the closest encounter on July 9. Resolutions ranged from about 100 km to about 20 km. Of the eight plumes seen on Voyager 1 imagery, six were still active, one (the largest seen by Voyager 1, 280 km high) was definitely quiescent, and the state of activity of another could not be determined. Most of the plumes seemed to be about the same size as they were on Voyager 1 imagery, but the largest currently active plume had grown to roughly 150 km from its approximately 100 km height of 4 months earlier. No new eruption sites were discovered, but preliminary analysis indicates that some fairly large-scale changes in surface morphology (visible at resolutions of 40-50 km) have taken place in the past 4 months, both around active vents and in other areas.