Alfvénic interaction along the Enceladus flux tube and its distant tail: Cassini’s in-situ multi-instrument observations

The Cassini spacecraft has provided clear evidence that Enceladus and Saturn are electrodynamically coupled, through energetic ion measurements by the Magnetospheric Imaging Instrument (Jones et al. 2006; Roussos et al. 2007; Andriopoulou et al. 2014), thermal electron measurements from the Cassini Plasma Spectrometer (CAPS), and the EUV and FUV emission measurements by the Ultraviolet Imaging Spectrograph (Pryor and Rymer et al., 2011, Pryor et al., 2024), large-scale perturbations to the low-frequency magnetic field from MAG (Dougherty et al. 2006), and high-frequency plasma waves from the Radio and Plasma Wave Science Investigation (RPWS, Gurnett et al., 2011; Sulaiman et al., 2018). However, a systematic investigation of the detailed electromagnetic interactions between Enceladus and Saturn with all Cassini measurements has yet to be carried out.

Between 2004 and 2017, the Cassini spacecraft sampled the magnetic field lines connected to Enceladus’ orbit, offering a unique opportunity to investigate this coupling in detail. In this study, we explore the interaction region(s) between Saturn and Enceladus using comprehensive data from MAG, RPWS and electron instruments CAPS/ELS and MIMI/LEMMS. We report on 15 case studies that reveal enhanced Alfvénic activity linked to Enceladus, including the main Alfvén wing (MAW) and reflected Alfvén waves (RAW) in the moon’s tail. These observations not only shed new light on the spatial extent of the electrodynamic coupling between Saturn and its icy moon, but also show for the first time that the tail of Enceladus extends and persists up to about 100 Enceladus radii downstream of the moon illustrating the extensibility of the coupling processes with the gas giant Saturn.