THE EVOLUTION OF JUPITERS RADIATION BELTS AFTER THE IMPACT OF COMET-DSHOEMAKER-LEVY-9

Radio telescope observations taken with the VLA and WSRT during the pe riod June-October 1994 show an East-West asymmetry which evolves over time. The E/W asymmetry is induced immediately following the first fra gment impact of comet Shoemaker-Levy 9. Following an impact, enhanceme nts are seen over a similar to 100 degrees range of Jovicentric longit udes at lambda(III) less than or similar to lambda(impact). Not all im pacts, however, induce longitudinal brightenings (large fragment G, fo r example, does not). The main radiation peak which brightened is usua lly displaced inward. However, the observed increase in flux density i s much smaller than predicted from conventional radial diffusion model s. The lower flux density is attributed to a loss of electrons due to pitch-angle scattering, field-aligned acceleration, and/or cross-L dif fusion. We show that the observed time evolution of the radio intensit y at each lambda(III) must result from a combination of the effect of the impact process on the electrons and electromagnetic environment (c hange in electromagnetic forces through, e.g., the excitation of plasm a waves), the particle drift around the planet, disappearance of parti cles in the loss cone, and absorption by Jupiter's ring. During the we ek of the SL9 impacts, the high-latitude emissions increased 30-40% mo re than the main radiation peaks, and each of the four peaks fluctuate d in intensity seemingly independent of the other three peaks, in cont rast to what one would expect under equilibrium situations for electro ns bouncing up and down the field lines. In contrast to the main radia tion peaks, which return to normal within a couple of days after impac t W, the high-latitude emissions continued to change for weeks after t he last impact. We suggest that this may have been caused by enhanced cross-field diffusion due to the presence of high-altitude dust, and/o r by pitch-angle scattering and cross-field diffusion of electrons tri ggered by long-lived plasma waves excited by the impacts, and/or by im pact-induced changes in the Alfven wings from the moon Amalthea, throu gh a change in the Alfven velocity. (C) 1997 Academic Press.