Callisto (moon)

Hires PBR textures based on GalileoSSI and Voyager mosaic - USGS source. (From wiki:) Callisto, or Jupiter IV, is the second-largest moon of Jupiter, after Ganymede, and the largest object in the Solar System that may not be properly differentiated. Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass. It is not in an orbital resonance like the three other Galilean satellites - Io, Europa, and Ganymede - and is thus not appreciably tidally heated. Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward. Because of this, there is a sub-Jovian point on Callisto's surface, from which Jupiter would appear to hang directly overhead. It is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt. Callisto is composed of approximately equal amounts of rock and ices.