7/9/79 560,000 km (350,000 mi)
Amalthea was observed end-on in the Voyager 2 picture, which has been computer-processed to enhance the image.
3/4/79 377,000 km (234,000 mi)
Io, Jupiter’s innermost Galilean satellite, displays great diversity in color and brightness. This Voyager 1 four-picture mosaic shows Io’s complex coloration of red-orange, black, and white regions, and the two major topographic features: volcanic regions, the most prominent of which is the “hoofprint” (volcanic deposition feature) in the center-right, and the intervolcanic plains that are relatively featureless. Io’s vivid coloring is probably due to its composition of sulfur-rich materials that have been brought to the surface by volcanic activity.
3/5/79 129,600 km (80,500 mi)
The bright area at the upper right in this Voyager 1 picture of Io appears to be a caldera (collapsed volcano) that is venting clouds of gases. The clouds may condense to form extremely fine particles that scatter light and appear blue. Because the infrared spectrometer discovered sulfur dioxide on Io, scientists believe this gas may be the main component of the clouds. Sulfur dioxide clouds would rapidly freeze and snow back to the surface. It is also possible that dark areas in the floors of the calderas are pools of encrusted liquid sulfur.
3/5/79 66,000 km (41,000 mi)