Saturn's ionosphere and D ring electrodynamic interaction using RPWS/LP measurements from the Cassini Grand Finale

We present the electron density altitude profiles of Saturn's ionosphere at equatorial latitudes (-15o ≤ φ ≤ 15o) and the ring shadowing effects from all the 23 proximal passes of Cassini's Grand Finale. The data are collected by the Langmuir probe (LP) and for some cases from the plasma wave frequency characteristics of the Radio and Plasma Wave Science (RPWS) 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 (winter) and northern (summer) hemispheres. We show a layered electron density altitude profile with evidence in the southern hemisphere of an electrodynamic type of interaction with the planets innermost D ring. Similar layers were observed during the Final Plunge of Cassini, where the main ionospheric peak is crossed at ∼ 1550 km altitude. Moreover, from the ring shadow signatures on the total ion current collected by the LP, we reproduce the A and B ring boundaries and confirm that they are optically thicker than the inner C and D rings and the Cassini Division to the solar extreme ultraviolet radiation. Furthermore, observed variations with respect to the inner edge of the B ring shadow imply a delayed response of the ionospheric H + because of its long lifetime and/ or suggest the presence of ring-derived plasma from the C and D rings reducing the shadowing signatures.