Two of three anomalous crater chains on Ganymede are shown here. The chain on the left is 60 km long, and the chain on the right is 160 km long. Note the "splash pattern" around and emanating away from the crater chains. It has been surmised that the pattern on the left is indicative of something having been hit on the surface and exploding causing the depression in the approximate shape of what was there. The picture on the right is surmised to have been something that was hit above surface and exploded showering material in the pattern that we see. For a sharper image of the right crater chain pull the top bar down exposing the image.
Photo Credit: Planetary Photojournal, JPL, Galileo