Harbour Ocean Natural color view of Ganymede from the Galileo spacecraft during its first encounter with the satellite. North is to the top of the picture and the sun illuminates the surface from the right. The dark areas are the older, more heavily cratered regions and the light areas are younger, tectonically deformed regions. The brownish-gray color is due to mixtures of rocky materials and ice.
Bright spots are geologically recent impact craters and their ejecta.
The finest details that can be discerned in this picture are about 13.4 kilometers across. A thick layer of melted, salty water somewhere beneath Ganymede's icy crust would be the best way to explain some of the magnetic readings taken by NASA's Galileo spacecraft during close approaches to Ganymede in May 2000 and earlier, according to one new report. In addition, the types of minerals on parts of Ganymede's surface suggest that, in the past, salty water may have emerged from below or melted at the surface, according to a study of infrared reflectance measured by Galileo. Third, new Galileo images of Ganymede hint how the water or slushy ice may have surfaced through the fractured crust, reminiscent of linear features on Europa, a neighboring moon believed likely to have a deep ocean beneath its ice. They include the most detailed photos ever taken of Ganymede and an animated virtual flyover of an area where a smooth, bright swath resembling parts of Europa cuts across older, more heavily cratered terrain.