An empirical model for Saturn’s plasma environment within the TRAPPED framework

As part of the ESA Testbed for Radiation and Plasma Planetary Environments (TRAPPED) project, we present the first empirical-based specification model of Saturn’s plasma environment based on the analysis of all publicly available plasma moment datasets derived using multiple techniques from Cassini observations made by the Cassini Plasma Spectrometer (CAPS) and the Radio and Plasma Wave Science (RPWS) instrument covering the entire 13-year mission.

We investigate the variability and spatio-temporal dynamics of the plasma moments with respect to various magnetic parameters including minimum normal distance to the current sheet, L-shell, latitude, and magnetic local time, and find the latter three parameters to be the most useful to organize the TRAPPED model plasma moments. The model moments include electron (cold and hot populations) and ion densities, temperatures and 3-dimensional ion velocities. We do not identify any clear variations with local time, despite previous Cassini-era studies indicating a local time variation related to an identified electric field in Saturn’s inner magnetosphere. Furthermore, our moment analysis results are consistent with seasonal and/or solar cycle modulation as reported in previous studies.

Despite the difference in the number of available observations between the Cassini mission and the Voyager 1 and 2 flybys, comparison of the TRAPPED model moments with moments derived from Voyager Plasma Science Experiment (PLS) observations are in relatively good agreement, which would suggest that there is no significant secular variation in Saturn’s magnetosphere, also consistent with previous Cassini-era studies.

Given that ambient magnetospheric plasma in planetary systems can induce spacecraft surface charging, it is imperative to develop a thorough understanding of planetary plasma environments to prepare for future space missions. ESA have recently highlighted Enceladus as a ‘top target’ for a future large-class mission, and thus this model will be used to support the planning and development of a future space mission to the Saturnian system.