MAGNETIC MAPPING OF AURORAL SIGNATURES OF COMET-SL9 IN THE JOVIAN-MAGNETOSPHERE

The electrodynamic interaction of comet Shoemaker-Levy 9 (SL9) with th e Jovian magnetosphere gave rise to the detection of several unique ph enomena in the UV, X-ray and radio wavelength ranges. Among them, the detection of an unusual FUV I bright spot in Hubble Space Telescope im ages of the southern polar cap on July 20, just before P2 collision, m ay be attributed to auroral-like processes triggered I by the charged environment of the comet fragments. We model here in detail the time-v arying morphology of the instantaneous magnetic field lines passing th rough the comet fragments during their crossing of the magnetosphere, with special focus on the location of the magnetic footprint and the n ature of the field line. We show that the FUV bright spot, not corotat ing with the planet, is likely to be related with a fragment still in the magnetosphere, and that fragment Q is the most presumable source o f the interaction, as its footprint can easily be resolved from fragme nt 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, w as on an open magnetic field line at the time of the observations, in agreement with the absence of observable conjugate emission in the nor th. But, the deformation of the magnetic held line passing through Q d uring the following few hours is such that it presumably became closed to the northern hemisphere during two separate periods between the ob servations under study and fragment Q's collision. A series of X-ray b ursts detected in the north precisely during the first of these period s could be related to the same process and strengthen our identificati on. A second FUV set of data was taken during the same period of close d field lines, but due to an unfavourable viewing geometry, the identi fication of observed bright spots I-with fragment Q footprint is more ambiguous. Finally, we estimate crudely the energy of the particles pr ecipitating in the FUV spot, and discuss briefly possible plasma proce sses. (C) 1997 Elsevier Science Ltd.