Unlike Europa and Io, Ganymede is not undergoing tidal heating today. The global geography of Ganymede is shown in this view obtained from 2.5 million kilometers by Voyager 2. The surface is roughly equally divided between relatively dark terrain, which is heavily cratered and relatively old, and bright terrain, which is younger and has been deformed tectonically. The large, dark, oval-shaped mass is Galileo Regio. While most of Ganymede is relatively brownish in color, possibly due to the contamination of the icy surface by meteoritic material, these polar frosts are more neutrally colored.
Bright spots are fresh, young impact craters and their ejecta patterns.
These views of bright terrain are the highest resolution images obtained on Ganymede. Grooves are typically 5 to 10 kilometers across, and in some areas appear to be comprised of parallel blocks of crustal material separated by faults. They resemble similar structures seen in Canyonlands National Park, Utah. Grooves are common on bright terrain and are generally believed to be due to extension of the surface. The cause and the amount of this extension are poorly known, but will be investigated by Galileo.