ENERGETIC PARTICLE SIGNATURES AT GANYMEDE - IMPLICATIONS FOR GANYMEDEMAGNETIC-FIELD

The second encounter of the Galileo satellite with the Galilean moon G anymede provided energetic particle measurements showing effects due t o the presence of that moon. Jovian corotation signatures, present on approach to and departure from the Ganymede system, suddenly become mu ch smaller when Galileo enters what has been termed Ganymede's magneto sphere. The location of these transitions agrees with magnetopause cro ssings identified by the magnetometer and plasma wave instruments. In Ganymede's magnetosphere, energetic ion and electron distributions dis play loss cone signatures whenever the Energetic Particles Detector (E PD) views along the magnetic field line. The loss cone measurements ar e used to estimate Ganymede's surface magnetic field along the satelli te track. The results agree with model projections to Ganymede's polar cap and support the existence of a Ganymede-intrinsic magnetic field. An evolution from Single to double loss cone also occurs with increas ing electron energy.