Galileo has eyes that can see more than ours can. By looking at what we call the infrared wavelengths, the NIMS (Near Infrared Mapping Spectrometer) instrument can determine what type and size of material is on the surface of a moon. Here, 3 images of Ganymede are shown.
Left: Voyager's camera.
Middle: NIMS, showing water ice on the surface. Dark is less water, bright is more.
Right: NIMS, showing the locations of minerals in red, and the size of ice grains in shades of blue.