ARC-1979-A79-7085

P-21756 BW only Range: 120,000 km (right) 169,000 km (left) Right: In the foreground of this picture taken by Voyager 2, the part of the surface of Ganymede shown is the typical grooved terrain as seen by Voyager 1. It consists of mutually intersecting bands of closely-spaced, parallel ridges and grooves. In the background is newly-cratered dark terrain across which can be traced several widely spaced parellel linear features. When viewed from a distance the line features appear to trace broad circular areas. The features resemble the circular ridges on Callisto that surround an almost complete annealed impact basin. The feature on Ganymede may be of similar origin but all traces of the impact itself have been destroyed. Left: This picture of Ganymede shows that the dark contrast terrain is separated by bright bands of grooved terain. The band of closely spaced linear grooves in the foreground is 150 km across and appears to be offset by another narrow band at right angles, as though by faulting. A variety of ray patterns are seen around the craters. One is in the left of the picture, it has prominent dark rays around an inner bright halo. Other craters have dark haloes; others have diffuse bright rays. The variation of albedo patterns around the craters may be indications of layering in the surface materials. The intensity of the craters suggests the dark areas are extremely old. The bright grooved terrain is less cratered and probably somewhat younger.