Magnetic mapping of auroral signatures of comet SL9 in the Jovian magnetosphere

Abstract

The electrodynamic interaction of comet Shoemaker-Levy 9 (SL9) with the Jovian magnetosphere gave rise to the detection of several unique phenomena in the UV, X-ray and radio wavelength ranges. Among them, the detection of an unusual FUV bright spot in Hubble Space Telescope images of the southern polar cap on July 20, just before P2 collision, may be attributed to auroral-like processes triggered by the charged environment of the comet fragments. We model here in detail the time-varying morphology of the instantaneous magnetic field lines passing through the comet fragments during their crossing of the magnetosphere, with special focus on the location of the magnetic footprint and the nature of the field line. We show that the FUV bright spot, not corotating with the planet, is likely to be related with a fragment still in the magnetosphere, and that fragment Q is the most presumable source of the interaction, as its foot-print can easily be resolved from fragment P2's, and also, although less easily, from the more distant fragment R to W's ones. We show also that Q, as well as the other fragments, was on an open magnetic field line at the time of the observations, in agreement with the absence of observable conjugate emission in the north. But, the deformation of the magnetic field line passing through Q during the following few hours is such that it presumably became closed to the northern hemisphere during two separate periods between the observations under study and fragment Q's collision. A series of X-ray bursts detected in the north precisely during the first of these periods could be related to the same process and strengthen our identification. A second FUV set of data was taken during the same period of closed field lines, but due to an unfavourable viewing geometry, the identification of observed bright spots with fragment Q footprint is more ambiguous. Finally, we estimate crudely the energy of the particles precipitating in the FUV spot, and discuss briefly possible plasma processes.