• 2410km radius satellite of Jupiter discovered by Galileo in 1610. A favourite target for observation by amateur astronomers, it has been viewed spectacularly by space probes in its 1.9 million km radius orbit. Callisto has a low average density of 1.8 gm/cc and is thought to consist of ice (and possibly water below the surface) surrounding a rocky core. The surface of Callisto, the largest of the Galilean satellites, is marked with bright impact craters, of which Valhalla is the most conspicuous.

Not what you were looking for?