A model of the Jovian internal field derived from in-situ and auroral constraints

The internal magnetic field of Jupiter is known to be highly multi-polar, not only from the direct measurements performed by the Voyager and Pioneer probes but also from the unusually complex shape of the northern auroral oval. The limited amount of data obtained from the Voyager and Pioneer flybys do not permit accurate determination of the topology of the magnetic field, as they barely constrain, even the octupole contribution to the field. This does not allow one to reproduce the position of the auroras nor satisfactorily explain the shape and frequency range of the Jovian radio arcs. Successive attempts have been made to constrain the higher-order field using the position of the Io auroral footprint where the auroras are due to currents generated close to Io and carried along the magnetic field lines. Thus, the auroral spots should map to Io’s orbit. VIPAL, the latest model of this kind is a 5th order model. However, the VIPAL model was limited by three factors: the main constraints come from a unique L-Shell, the difficulty of mixing jovigraphic and magnetic data, and the non-linearity of the problem. These issues lead to numerically-demanding computations, with the scale of computation increasing as the square of the model order. We have developed a new method for computing the magnetic field using in-situ and auroral constraints (ISaAC) which we have applied to the computation of the Jovian magnetic field, based on Voyager, Pioneer, Galileo magnetic measurements and constrained by Io’s, Europa’s and Ganymede’s auroral footprint locations.