Io's interaction with the Jovian magnetosphere

When the Galileo orbiter passed within I000 km of lo on December 7, 1995, the data collected were every bit as exciting as the Galileo team had expected, given the unique interaction between lo and the Jovian magnetosphere. The spacecraft detected intense beams of electrons propagating parallel to the magnetic field and a variety of unexpectedly strong wave phenomena surrounding lo that are associated with lo's production of new ions. There was also evidence for an intrinsic magnetic field, possibly generated by a dynamo within Io, and a cool 'ionospheric ' plasma directly behind Io, removing tens of kilograms of material per second, a fraction of the nearly a ton per second, added to the torus as a whole. lo had already called attention to itself by controlling decametric wavelength radio emissions. Previous attempts to explain this control assumed that the movement of lo, an object with high electrical conductance, through the Jovian magnetic field leads to falling electrical potential, particle acceleration, and a field-aligned current system coupling lo to the Jovian ionosphere. The force generated by the electrodynamic interaction is thought to accelerate lo in its orbital motion and slow the rotation of the Jovian ionosphere. The magnetic flux tube that threads through lo thus plays a critical role in the coupling of lo and Jupiter. Since lo's orbital motion is not synchronous with Jupiter's spin, the lo flux tube slips with respect to Jupiter and/or lo. Such slippage may result in an electric fiel