Analysis of midlatitude auroral emissions observed during the impact of Comet Shoemaker-Levy 9 with Jupiter

During the impact of Comet Shoemaker-Levy 9 fragment K on Jupiter observers detected aurora-like emissions near the impact region as well as in the ot her hemisphere at approximately magnetic conjugate positions equatorward of auroral latitudes. A number of generation mechanisms were suggested, but i nvestigations of their significance have been hampered by a lack of knowled ge about the jovian internal magnetic field, the exact timing, and the geom etry of the impact and emission sites. We use the VIP 4 model of the intern al magnetic field, high-time-resolution calculations of the fragment K traj ectory, and images from the Hubble Space Telescope Wide Field Planetary Cam era 2 with advanced processing to reanalyze the relationship between these emissions. The impact location is enclosed to the north and south by two re gions of enhanced far-ultraviolet emissions reaching a maximum distance of 18,000 km south of the impact site roughly along the line of the incoming f ragment's trajectory. The southern region can be further divided into two s ubregions, which partly overlap with magnetic projections of two brighter e mission regions observed in the northern hemisphere close to the line of fo otprints of Amalthea. The area of the southern region approximates the area of these projections. No enhanced emissions are found conjugate to the imp act site and the northward emission region. The magnetic projections sugges t that the Gossamer ring scattered particles coming from the region southwa rd of the impact site and prevented precipitation from the northward region into the northern hemisphere. Particle acceleration by upward accelerating shocks seems feasible to explain the geometry of the southern and northern hemispheric emission regions if we assume that a part of the plume bounced twice and provided enough energy at its second bounce to also generate sho ck waves. (C) 1999 Academic Press.