Investigating Dawn/Dusk Asymmetries in Saturn’s Southern Aurora

Farr, Sam and Badman, Sarah and Ray, Licia C and Provan, G. and Cowley, S.W.H. (2025) Investigating Dawn/Dusk Asymmetries in Saturn’s Southern Aurora. In: IAGA / IASPEI Joint Scientific Meeting 2025, 2025-08-31 - 2025-09-05, Instituto Superior de Engenharia de Lisboa (ISEL).

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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. Notably, MAG data revealed asymmetric signatures between inbound and outbound passes in the dawn and dusk sectors respectively – suggesting varying field-aligned current (FAC) structures. Similar asymmetries have been observed in ultraviolet imaging. Given that Saturn’s magnetic field is highly symmetric, with a FAC structure largely driven by plasma subcorotation that is also symmetric within the inner magnetosphere, these asymmetries suggest some additional outer magnetospheric or acceleration-region processes are driving these variable features at broadly fixed local times. Using data from Cassini MAG, we first process MAG data to determine ionospheric currents, whose gradient indicates FAC structure directed radially upward or downward. Orbits are categorized based on general FAC patterns, and each pass is individually analysed to assess its consistency within its group, variations across local times, and any correlation between FACs and auroral enhancements observed using Cassini UVIS, and/or Hubble Space Telescope STIS datasets, where images exist. By comparing these groups generally, we investigate whether auroral enhancements and local time differences, or similarities, correlate with specific FAC structures. Additionally, we examine the dependence of Saturn’s planetary period oscillation (PPO) FACs on these structures. Finally, our findings are compared with previous studies to identify potential variations over longer timescales and differences between hemispheres. This work highlights the lack of axial symmetry in Saturn’s FAC system and shows the complexity of duskside auroral dynamics.