Structure and Behaviour of Saturn’s Field-Aligned Currents in the Southern Dusk Sector

Farr, Sam and Badman, Sarah and Ray, Licia C and Provan, G. and Cowley, S.W.H. (2025) Structure and Behaviour of Saturn’s Field-Aligned Currents in the Southern Dusk Sector. In: Autumn MIST 2025, 2025-11-28 - 2025-11-28, Geological Society of London, Burlington House, Piccadilly.

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Abstract

In 2017, the final orbits of the Cassini–Huygens mission provided 22 low-altitude passes through Saturn’s auroral region. Saturn’s aurorae are known to be modulated by the solar wind, the rotation of the magnetosphere, and a pair of field-aligned current systems (FACs) called the planetary period oscillation currents (PPOs). We investigate the relative influence of these drivers and asymmetries between inbound (dawn sector) and outbound (dusk sector) passes. We determine field-aligned currents on field lines mapping to 18°–25° colatitude across 17.5–22.5 hr local time in the south. Within this region, upward-directed FACs are on average 1.9 times more frequently observed than downward FACs. Modelling the PPO systems, referred to as northern and southern, shows both systems variably influencing the southern FACs across our colatitude range. Four passes occurred during solar wind compressions. Those nearest the compression onset show the strongest currents and pronounced FAC filamentation, while later passes exhibit reduced filamented structure but increased plasma angular velocity. Our results highlight the complexity of dusk-side auroral dynamics and demonstrate that distinct behaviours arise under specific magnetospheric conditions.