Vertical Structure of the Ionosphere and Upper Neutral Atmosphere of Saturn from the Pioneer Radio Occultation

Abstract

Radio occultation measurements at S band (2.293 gigahertz) of the ionosphere and upper neutral atmosphere of Saturn were obtained during the flyby of the Pioneer 11 Saturn spacecraft on 5 September 1979. Preliminary analysis of the occultation exit data taken at a latitude of 9.5 degrees S and a solar zenith angle of 90.6 degrees revealed the presence of a rather thin ionosphere, having a main peak electron density of about 9.4 x 10/(3) per cubic centimeter at an altitude of about 2800 above the level of a neutral number density of 10(19) per cubic centimeter and a lower peak of about 7 x 10(3) per cubic centimeter at 2200 kilometers. Data in the neutral atmosphere were obtained to a pressure level of about 120 millibars. The temperature structure derived from these data is consistent with the results of the Pioneer 11 Saturn infrared radiometer experiment (for a helium fraction of 15 percent) and with models derived from Earth-based observations for a helium fraction by number of about 4 to 10 percent. The helium fraction will be further defined by mutual iteration with the infrared radiometer team.

Saturn's Ionosphere: Electron Density Altitude Profiles and D‐Ring Interaction From The Cassini Grand Finale

“…Prior to the Grand Finale, the final phase of the Cassini mission, no in situ measurements of the Kronian ionosphere had been made. Properties of Saturn's ionosphere were inferred based on three different remote observation methods: radio occultation (Kliore et al, , , ; Nagy et al, ), radio emission from Saturn electrostatic discharges (Fischer et al, ; Kaiser et al, ), and millimeter‐band observations of protonated molecular hydrogen ( ; O'Donoghue et al, ). However, only the radio occultation technique has yielded the altitude structure of the electron density.…”

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

“…Early Saturn 31 ionospheric models (e.g., McElroy, 1973;Capone et al, 1977) predicted electron densities an 32 order of magnitude larger than those later measured by the Pioneer 11 and Voyager spacecraft 33 (Kliore et al, 1980;Kaiser et al, 1984;Lindal et al, 1985). One chemical effect of introducing 34 oxygen bearing compounds into Saturn's upper atmosphere is to convert H + -a long-lived major 35 atomic ion in outer planet ionospheres -into a short-lived molecular ion that quickly 36 dissociatively recombines, thereby reducing the net electron density.…”

The ionospheres–thermospheres of the giant planets

“…Fig. 2 shows the deduced ionospheric n e profiles for Saturn from the Pioneer 11 (Kliore et al, 1980) and Voyager 1 and 2 (Lindal et al, 1985) RSS experiments. The Pioneer data revealed multiple n e (Lindal et al, 1987) and Neptune (Lindal, 1992) have been observed by the Voyager 2 radio occultation experiments.…”