Discovery of Ganymede's magnetic field by the Galileo spacecraft

The encounter of Galileo spacecraft with Ganymede, Jupiter's largest moon reveals the the presence of an internal magnetic field. The data agrees with the observation of an equatorial surface field strength of 750 nT and a 10 degree tilt of Ganymede-centered magnetic dipole with respect to the spin axis. The magnetic field is strong enough to produce a magnetosphere with well-defined boundaries in Ganymede. The observations fail to indicate the source of the internal magnetic field.