Off-equatorial Electron Trajectories in Ganymede’s Magnetosphere: Implications for a Bifurcated Ring Current Under Different Jovian Wind Conditions

Abstract Ganymede, Jupiter’s largest moon, hosts a minimagnetosphere sustained by its intrinsic magnetic field and embedded in the sub-Alfvénic Jovian plasma flow, providing a unique natural laboratory for studying energetic particle behavior. By combining a test-particle model with three-dimensional, high-resolution magnetohydrodynamic simulations, we analyzed energetic electron drift motions under G8, G28, and G29 upstream conditions. Key findings include: First, we show that Ganymede’s magnetosphere supports not only the typical equatorial trajectories of energetic electrons but also novel off-equatorial ones, as a consequence of strong Jovian wind compressions under all upstream plasma conditions. Second, equatorial and off-equatorial trajectories confine electrons to drift shells at different latitudinal regions, implying that the electron ring current may adopt a bifurcated configuration. Third, the ring current manifests short-timescale disturbances associated with intermittent magnetopause reconnections, which are modulated by a 10 hr periodicity driven by Jupiter’s rotation. While in situ particle measurements remain limited, our results provide new insights into the structure and variability of Ganymede’s electron ring current, awaiting confirmation by the ongoing JUICE mission.