Magnetic field analysis s
Magnetic field analysis shows that this moon may contain a salty ocean 200 kilometers underground. Its major sites include the crater chain Gipul Catena, and the Valhalla Region, one of the largest impact features in the solar system.  Though it has both the oldest and most heavily cratered landscape in the solar system, it has no large mountains and next to no tectonic or volcanic activity.  Like its three companions, it was discovered by Simon Marius in 1610.  FTP, identify this second-largest and outermost Galilean moon of Jupiter.
Magnetic field analysis shows that this moon may contain a salty ocean 200 kilometers underground.
Callisto