Dark material and few small craters on Callisto

Dark material and few small craters on Callisto

Fig. 9.25 . A dark, mobile blanket of fine material covers Callistoís surface, sometimes collecting within crater walls. While Jupiterís moon Callisto is saturated with large impact craters, it has fewer very small craters when compared with the Earthís Moon and Mercury. One explanation is that the smaller craters have been filled by dark material that has moved down surface slopes. An alternative explanation for the paucity of little craters on Callisto is that there were fewer small impacting objects in its vicinity when compared with the amount within the inner solar system. This image, about 74 kilometers across, was taken from the Galileo spacecraft on 17 September 1997. (Courtesy of NASA/JPL.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University