Comparison of the electron density measurements in Titan’s ionosphere

Electron density is one of the most important measurable parameters in space plasma. The electron density provides important information about the local plasma properties at Titan, constraining the plasma wave propagation, possible photochemical reactions and effectiveness of the energy-momentum processes. Therefore, the accurate measurement is critical for the understanding of the general structure and dynamics of Titan’s plasma environment. Cassini-Huygens performed 126 close flybys of Titan, performing both active and passive measurements of the electron density. In this study, we focus on the Radio and Plasma Wave Science (RPWS) instruments, such as the Langmuir probe and electrical antennas, and the comparison of the derived electron density values in Titan’s ionosphere. We show that the estimates from the electrical antennas (using the identification of the upper-hybrid resonance line) systematically overestimate the electron density in the lower ionosphere of Titan. We propose that the main cause is the inability to identify precisely the upper-hybrid resonance line. Moreover, the upper-hybrid line splits into the upper- and lower-band, with the lower-band identified as the upper-hybrid wave and the upper of unknown origin. After the electron density correction, we find that the overestimation comes from the wrong identification of the upper-hybrid line, and show that the corrected electron densities are overestimated, but by the LP. We discuss possible reasons for the discrepancy and recommendations on how to implement corrections to the analysis.