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P. N. Romani (NASA - Goddard Space Flight Center), I. de Pater, D. Dunn (Astronomy Dept., Univ. of Calif. Berkeley), K. Zahnle (NASA - Ames Research Center), B. Washington (Morehouse College / Georgia Tech.)
Recent comparison of ground based microwave observations to Galileo probe data has shown that if the ammonia (NH3) mixing ratio in Jupiter's atmosphere is 3.6 times solar for P > 8 bar globally on the planet, then the mixing ratio must decrease at pressures less than or equal to 4 bars and reach subsolar values (approximately 0.5 times solar) at pressures less than or equal to 2 bars (de Pater et al. submitted to Icarus). The two probable cloud sinks for vapor phase NH3 are the aqueous ammonia solution cloud and the ammonium hydrosulfide (NH4SH) cloud. Since NH4SH formation is equal molar with ammonia and hydrogen sulfide (H2S) and the hydrogen sulfide mixing ratio is less than the ammonia mixing ratio, it is not possible for NH4SH formation to be a significant sink for NH3 in Jupiter's atmosphere. However, in early laboratory measurements of NH4SH formation at least one experimenter was convinced that NH3 was being adsorbed unto NH4SH crystals, opening up the possibility that each H2S could remove more than one NH3 molecule from the vapor phase in the region where NH4SH cloud particles are present. In support of this hypothesis, reactions of NH3 with compounds similar to H2S form compounds analogous to NH4SH (e.g. NH4I, NH4Cl, and NH4Br) which can adsorb up to 6 NH3 molecules per molecule of compound. While the necessary chemical thermodynamic data are lacking for the adsorption of NH3 unto NH4SH to explore this possibility definitively we can make estimates based upon the analogous compounds where the thermodynamic data is available. The results of this study for Jupiter and its implications for the other giant planets will be presented.
The author(s) of this abstract have provided an email address for comments about the abstract: Paul.Romani@gsfc.nasa.gov