Problem description:

One of the surprises of the Galileo mission was the discovery of an internal magnetic field at Ganymede [Kivelson et al., 1998], which was strong enough to keep of the magnetic field of the Jupiter and create its own mini-magnetosphere inside of Jupiter?s.  After several flybys it became clear that Ganymede?s magnetosphere was like any other magnetosphere in the solar system. The plasma wave experiments showed familiar radiation (e.g. whistler waves) [Gurnett et al., 1996] generated by trapped ring current electrons, which were also detected directly by the energetic particle experiment [Paranicas et al., 1999]. Deep penetration into the magnetosphere showed that also field line resonances exist [Volwerk et al., 1999]. Ganymede?s field is oppositely directed to Jupiter?s field. The oncoming magnetoplasma pushes on the upstream side of the magnetosphere, compressing it. It was expected that continuous reconnection takes place at the upstream side of the moon. Numerical modeling however has shown that reconnection is patchy and moves around over the upstream magnetopause [Jia et al., 2009]. On the downstream side of the moon, the magnetic field is stretched into a tail like shape. Also the time varying magnetic field of the Jovian magnetosphere (because of Jupiter?s tilted dipole) could induce a magnetic field in the subsurface ocean of Ganymede [Kivelson et al., 2002].