Callisto the moon

Also a moon of the planet Jupiter. Callisto was discovered in 1610 by Galileo Galilei, and is the most heavily cratered moon in the solar system. It is also the third-largest moon in the solar system, about the same size as the planet Mercury.

Recent observations of Callisto's magnetic field by the Galileo probe suggests that Callisto may posses a salty ocean of liquid water underneath a crust of ice approximately 200 kilometers thick. Below this ocean is an unusual core that is thought to be an almost uniform mixture of rock and ice. Callisto has the lowest density of the four Galilean moons of Jupiter, only 1.86 gm/cm³.

Statistics for Callisto:

 Mass (kg)                          1.08e+23
 Equatorial radius (km)             2,400
 Surface area (square km)           72e+6
 Mean distance from Jupiter (km)    1,883,000
 Rotational period (days)           16.68902
 Orbital period (days)              16.68902
 Mean orbital velocity (km/sec)     8.21
 Orbital eccentricity               0.007
 Orbital inclination (degrees)      0.281
 Escape velocity (km/sec)           2.45