Jupiter's satellite Callisto

Jupiter

. This Voyager 1 image shows the heavily cratered surface of Callisto. Its icy crust is as rigid as steel, and it therefore retains the scars of an ancient bombardment by impacting meteorites. An exceptionally large meteorite sent waves rippling across the surface, like a rock dropped into a pond. The extensive system of concentric rings, extending about 1.5 million meters form the impact site (top center), is named Valhalla after the home of the Norse gods.. The impacting object apparently punctured the surface and disappeared. Today only the frozen, ghostlike ripples remain. Although there are very few large craters, the rest of Callisto is pockmarked with smaller impact craters that are flat for their size, and many of them have bright rims that resemble clean water ice splashed upon the dirtier surface ice. (Courtesy of JPL and NASA.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University