Cassini Radio Occultations of Saturn's Ionosphere: Modeling the Impact of Water

Details Cassini Radio Occultations of Saturn's Ionosphere: Modeling the Impact of Water Cassini Radio Occultations of Saturn's Ionosphere: Modeling the Impact of Water

Sep 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dps....38.1124m&link_type=abstract

American Astronomical Society, DPS meeting #38, #11.24; Bulletin of the American Astronomical Society, Vol. 38, p.500

Astronomy and Astrophysics

Astronomy

Scientific paper

The Saturn-Thermosphere-Ionosphere-Model (STIM), a global circulation model of Saturn's upper atmosphere, is used to investigate a range of possible parameters that could lead to the profiles measured recently by the Radio Science Subsystem (RSS) aboard Cassini. Specifically, electron density observations of Saturn's equatorial ionosphere demonstrate a dawn/dusk asymmetry, a possible double peak, and a high degree of vertical structure and variability. On average, peak electron densities are larger at dusk than dawn (5400 cm-3 vs. 1700 cm-3) and the peak altitudes are lower at dusk than dawn (1880 km vs. 2360 km). This study uses a 3D general circulation model along with self-consistent 1D water diffusion calculations to examine the possibility that a topside flux of neutral water into Saturn's atmosphere may provide a loss mechanism -- via charge exchange with protons -- that is sufficient to reproduce the observed ionosphere. Modeling results indicate that a constant background influx of (0.5 - 1.0) x 107 H2O cm-2 sec-1 is adequate in reproducing Cassini measurements, providing a good match to the main electron density peak as well as the dawn/dusk asymmetry. The structuring observed in the electron density profiles could result from brief surges and/or reductions in the background water flux, which ultimately may be linked to geysers near Enceladus’ southern pole.
STIM development at Boston University was funded by the NASA Planetary Atmospheres program, which also supported JDR. LM acknowledges support from a NASA Graduate Student Researchers Program fellowship, and IM-W is supported by a British Royal Society Fellowship. AJK and AFN acknowledge support from the Cassini Project Office.

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