On the water abundance in the atmosphere of Jupiter

Abstract

In this paper, we attempt to place constraints on the possible global abundance of water and the average vertical cloud structure in the atmosphere of Jupiter. Based on the analysis of the Galileo Near-Infrared Mapping Spectrometer data, we find that in the atmosphere of Jupiter down to 6–8bar, particularly in the North Equatorial Belt (NEB) region, the overall O/H ratio is compatible with one or more times the solar value of this ratio. We also find that if water clouds form at the levels where they are expected from thermochemical equilibrium calculations for a given deep O/H ratio, then subsolar values of the O/H ratio cannot be reconciled with the analyzed data. However, these results are dependent on the model atmosphere, in particular the detailed vertical distribution of cloud opacity. Therefore, they should be considered with care, until new observations on the vertical cloud structure become available. The water vapor mixing ratio in the NEB displays large spatial variations. The same set of data yield subsaturated mixing ratios of ammonia to atmospheric levels of about 4bar. This depletion of ammonia to great depths, as seen by the Galileo Probe in the hot spot where it entered, appears to be a common phenomenon in the entire NEB.