SL9 Impacts and Simulations of Enhanced Radial Diffusion

Abstract

We present detailed calculations on enhanced radial diffusion models and show that many, though not all, of the phenomena observed during the week that Comet Shoemaker–Levy 9 crashed into Jupiter can be explained by a sudden increase in the radial diffusion coefficient. Our calculations use estimates for the enhancement in the diffusion coefficient which come from self-consistent calculations of the electromagnetic turbulence generated by the impacts (Brecht et al. 2001, Icarus). These calculations suggest that the diffusion coefficient is enhanced at least a few million times above the nominal value during a short period of time (minutes). Our model shows that Jupiter's main radiation peaks brighten up much more than the high latitude regions, as is indeed observed following impacts during the first few days of the impact week. The calculations also suggest that the largest enhancements in intensity and largest inward shift of the radiation peaks occur at jovicentric longitudes ∼100°≲λ III≲250°, i.e., the longitude range where the B=constant contours are furthest from the planet. This longitude range agrees with the region where the strongest enhancements have indeed been observed. The dramatic increase in the intensity of the high latitude peaks following impacts which took place later in the week is attributed to a direct acceleration of electrons by the upward propagating shock. Finally, compared to the observations, the radial diffusion models predict much larger enhancements in the radiation peaks than observed. We attribute this, as well as the initial decrease in intensity on July 16–17, to a large loss of electrons caused by pitch angle scattering.