Saturn’s Ionosphere: Electron Density Altitude Profiles and Dâ Ring Interaction From The Cassini Grand Finale

Abstract

We present the electron density (ne) altitude profiles of Saturn’s ionosphere at nearâ equatorial latitudes from all 23 orbits of Cassini’s Grand Finale. The data are collected by the Langmuir probe part of the Radio and Plasma Wave Science investigation. A high degree of variability in the electron density profiles is observed. However, organizing them by consecutive altitude ranges revealed clear differences between the southern and northern hemispheres. The ne profiles are shown to be more variable and connected to the Dâ ring below 5,000Â km in the southern hemisphere compared to the northern hemisphere. This observed variability is explained to be a consequence of an electrodynamic interaction with the Dâ ring. Moreover, a density altitude profile is constructed for the northern hemisphere indicating the presence of three different ionospheric layers. Similar properties were observed during Cassini’s final plunge, where the main ionospheric peak is crossed at â ¼1,550â km altitude.Plain Language SummaryThe Cassini Langmuir probe measured directly the uppermost layer of Saturn’s atmosphere, the ionosphere, during its Grand Finale. The observations revealed a layered electron density altitude profile with evidence in the southern hemisphere of an electrodynamic type of interaction with the planet innermost Dâ ring. Moreover, the main peak of the ionosphere is observed for the first time in the final plunge around 1,550Â km.Key PointsCassini RPWS observations during the Grand Finale show an electrodynamic type of interaction between the topside ionosphere and the Dâ ring in the southern hemisphereA layered electron density profile is observed, characterized by at least a diffusive and a chemical equilibrium regionThe main ionospheric peak is observed around 1,550 km in the final plunge