Images of Amalthea in silhouette against Jupiter indicate that the satellite may be faceted or diamond shaped.
Volcanic activity on Io changed somewhat, with six of the plumes observed by Voyager 1 still erupting.
The largest Voyager 1 plume (Pele) had ceased, while the dimensions of another plume (Loki) had increased by 50 percent.
Several large-scale changes in Io’s appearance had occurred, consistent with surface deposition rates calculated for the large eruptions.
Europa is remarkably smooth with very few craters. The surface consists primarily of uniformly bright terrain crossed by linear markings and very low ridges.
There are four basic terrain types on Ganymede, including younger, smooth terrain and a rugged impact basin first observed by Voyager 2.
Callisto’s entire surface is densely cratered and is likely to be several billion years old.
Equatorial surface temperatures on the Galilean satellites range from 80 K (night) to 155 K (the subsolar point on Callisto).
Magnetosphere
The outer region of the magnetosphere contains a hot plasma consisting primarily of hydrogen, oxygen, and sulfur ions.