Its plume extends about 100 kilometers above the surface, and is being hit by sunlight just a little east of Io's eastern edge. Scattered light from Prometheus' plume and Io's lit crescent also contribute to the diffuse yellowish emission which appears throughout much of the sky. The mottled face of Jupiter's volcanically active moon Io, viewed by the Galileo spacecraft, shows dramatic changes since it was seen 17 years ago by the exploratory NASA spacecraft Voyagers 1 and 2 . Io's surface is covered with volcanic deposits that are thought to contain ordinary silicate rock, along with various sulfur-rich compounds that give the satellite its distinctive color. In the brighter areas the surface is coated with frosts of sulfur dioxide.
Dark areas are regions of current or recent volcanic activity.
Planetary scientists say many changes are evident in the surface markings since this region of Io was imaged 17 years ago by the Voyager spacecraft. The bright regions near the eastern limb of the moon are much more prominent in the Galileo images than they were previously. Masubi was discovered as an active volcano during the Voyager encounters of Io in 1979. Three full-disk color views of Jupiter's volcanic moon Io as seen by NASA's Galileo spacecraft camera are shown in enhanced color to highlight details of the surface. Comparisons of these images to those taken by the Voyager spacecraft 17 years ago has revealed many changes have occurred on Io.