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J. I. Moses (LPI), B. B\'ezard, E. Lellouch (Obs. Paris-Meudon), H. Feuchtgruber (MPI-EP), G. R. Gladstone (SwRI), M. Allen (JPL/Caltech)
We have developed one-dimensional photochemical models of Saturn's atmosphere to better understand the quantitative details of hydrocarbon and oxygen photochemistry on the outer planets and to determine the effects of extraplanetary debris on atmospheric chemistry. The models are compared with observations from the Infrared Space Observatory (ISO) to constrain Saturn's eddy diffusion coefficient profile and the influx of oxygen compounds to Saturn from micrometeoritic bombardment and other external sources. Results regarding the derived eddy diffusion coefficients, molecular abundances, dominant photochemical schemes, and the implied external influx of oxygen will be discussed in detail. Preliminary model abundances of CH3, C2H2, C2H6, CH3C2H, C4H2, CO2, and H2O reproduce emission features observed by ISO, and the model is also consistent with the upper limit derived for C3H8. On the other hand, the model-derived C2H4 column abundance is at least a factor of 2 too high, suggesting that the model may still have problems with the chemistry or eddy diffusion coefficient profile. The implied total oxygen influx (in terms of O atoms) from model-data comparisons of CO2 and H2O is 6±3 \times 106 cm-2 s-1. We find that the observed CO2/H2O ratio on Saturn cannot be reproduced if all the oxygen is entering the atmosphere in the form of water; some additional oxygen in the form of CO, CO2, or O is required. If all the oxygen is derived from the ablation of interplanetary dust particles, the implied dust flux at 9.5 AU (away from Saturn's gravitational influence) is (0.1-5)\times 10-17 g cm-2 s-1. The large range in the quoted values for IDP mass influx reflects uncertainties in the orbital properties of the dust.