This photomosaic of Ganymede, Jupiter's largest satellite, was taken on the morning of July 9, 1979, by Voyager 2 at a range of about 100,000 kilometers (62,000 miles).  It shows numerous impact craters, many with bright ray systems.  The rough mountainous terrain at lower right is the outer portion of a large fresh impact basin which post-dates most of the other terrain.  At bottom, portions of grooved terrain transect other portions indicating they are younger.  This may be the result of the intrusion of new icy material which comprises the crust of Ganymede.  The dark patches of heavily cratered terrain (right center) are probably ancient icy material formed prior to the grooved terrain.  The large rayed crater at upper center is about 150 kilometers (93 miles) in diameter.