Moon of Jupiter
Diameter: 4821 km
Distance: 1882700 km (mean)
Period: 16.689 days
Eccentricity: 0.007
Inclination: 0.31°
Magnitude: 5.7

Callisto, the outermost of the 'Galilean Satellites' was discovered in 1610 by Galileo Galilei. It is the third largest known moon with about the same diameter as the planet Mercury. Callisto's surface is heavily cratered and composed of nearly equal parts of rocky material and water ice.