Revealing the Large-Scale Properties of the Saturnian Magnetodisc Current Sheet

The presence of a rotating, internally sourced, equatorial current sheet plays a significant role in shaping the Saturnian magnetosphere. This work will show how the magnetodisc current sheet varies with respect to both spatial and temporal factors by tracking its large-scale properties throughout the complete Cassini mission.

We firstly determine a global stress state for Saturn by measuring the variable strength of the current sheet. Identifying perturbations in the inner magnetosphere, which are due to the changes in the current sheet strength, reveal when the system is stretched, compressed or near its ground state. We find that small scale stresses are continuously acting on the system, but infrequent large-scale perturbations are found, showing the dynamical nature of the Saturnian magnetosphere. An underlying local time variability was also discovered, revealing a more compressed noon and dusk region than at dawn, where the field is most stretched and the current sheet strength is largest.

We then turn our focus to the vertical structure of the magnetodisc current sheet, determining its thickness from direct measurements taken by Cassini as it made fast, steep crossings through the current sheet. We determine the global average value for the thickness, which is thinner than previously assumed, but identify variations due to both spatial and temporal factors. We find a radial profile for the thickness, whereby the magnetodisc current sheet thins with radial distance on the nightside but remains approximately constant on the dayside. However, there is significant variability about the average thickness values calculated, which points towards the existence of multiple underlying drivers. For instance, we see evidence for modulations of the thickness by the planetary period oscillations (PPOs) but with some discrepancy, most likely due to the influence of the solar wind.

With these results, we reveal the large-scale properties of the magnetodisc current sheet and how it shapes the Saturnian system.