Saturn ring rain: Model estimates of water influx into Saturn's atmosphere

摘要

Recently H-3(+) was detected at Saturn's low- and mid-latitudes for the first time (O'Donoghue et al. [2013]. Nature 496(7444), 193-195), revealing significant latitudinal structure in H-3(+) emissions, with local extrema in one hemisphere mirrored at magnetically conjugate latitudes in the opposite hemisphere. The observed minima and maxima were shown to map to regions of increased or decreased density in Saturn's rings, implying a direct ring-atmosphere connection. Here, using the Saturn Thermosphere Ionosphere Model (STIM), we investigate the "ring rain" explanation of the O'Donoghue et al. (O'Donoghue et al. [2013]. Nature 496(7444), 193-195) observations, wherein charged water group particles from the rings are guided by magnetic field lines as they "rain" down upon the atmosphere, altering local ionospheric chemistry. Based on model reproductions of observed H variations, we derive maximum water influxes of (1.6-16) x 10(5) H2O molecules cm(-2) s(-1) across ring rain latitudes (similar to 23-49 degrees in the south, and similar to 32-54 degrees in the north), with localized regions of enhanced influx near -48 degrees, -38 degrees, 42 degrees, and 53 degrees latitude. We estimate the globally averaged maximum ring-derived water influx to be (1.6-12) x 10(5) cm(-2) s(-1), which represents a maximum total global influx of water from Saturn's rings to its atmosphere of (1.0-6.8) x 10(26) s(-1). The wide range of global water influx estimates stems primarily from uncertainties regarding H-3(+) temperatures (and consequently column densities). Future ring rain observations may therefore be able to reduce these uncertainties by determining H-3(+) temperatures self consistently. (C) 2014 Elsevier Inc. All rights reserved.