Ionospheric effects of Comet Shoemaker-Levy 9 impacts with Jupiter

We study the thermosphere and ionosphere effects of the July 1994 Comet P/Shoemaker-Levy 9 impacts with Jupiter using a one-dimensional transport model which includes detailed neutral-neutral and ion-neutral chemistry and diffusive vertical transport for a variety of sulfur, nitrogen, and oxygen molecular species observed at the time of the impacts. The model uses a background neutral atmosphere based on the temperature profile obtained from Galileo probe measurements and a basic ionospheric model which satisfies current observational constraints on electron and H-3(+) densities. After the influx of impact-related neutral species into the ionosphere, new ion species such as S+, H3CS+, and NH4+ (and in some cases H3O+, SO+, and HCO+) appear along with the usual ionospheric species. Our model predicts that S+ begins to control the density of the ionospheric peak some hours after impact. The H p column density decreases by a factor ranging from 5 to 100, depending on the amount of water present. This is consistent with most nonauroral observations of H-3(+) emission during and just after the impact period. The model predicts electron density column enhancements of up to a factor of 10 for post-impact times less than a few days as well as significant abundances Of S-2 at the Galileo observational epoch, though at altitudes below ionospheric levels. Perhaps of more general interest is the compilation, presented here, of the ionospheric mechanisms involved in a comprehensive sulfur, nitrogen, and oxygen chemical model which may be of considerable use in future studies of ablation or particle precipitation in any hydrogen-dominated outer-planet ionosphere. (C) 2001 Elsevier Science (USA).