Check out this great animation found on the internet a while back that was compiled from images taken by the Cassini probe as it flew by Jupiter at the tail end of 2000. It used to be hosted at a U.S. astrogeology site which no longer exists and the animation was credited to Paul Geissler. Those glowing dots are active volcanoes. At the very end there is a blast of light from a crescent Io coming into view. The features are strikingly similar to those of the “dark side” image of Io published here during the New Horizons encounter, including the “auroral displays in Io’s tenuous atmosphere interacting with Jupiter’s magnetosphere”.
NOTE: The animation was cleaned up a bit by wanderingspace.net just for presentation purposes. This mostly included increasing the canvas size, removing all the surrounding noise and darkening the disc of Io itself.