Wednesday

Ganymede is the largest moon in the Solar System, and the only satellite to maintain a permanent magnetic field. Jovian plasma can enter the moon’s magnetosphere via magnetic reconnection at the upstream magnetopause, where Ganymede’s magnetic field lines are nearly anti-parallel to the Jovian field. Despite relatively steady magnetopause conditions, MHD numerical simulations have shown evidence of unstable reconnection events such as flux ropes. Nevertheless, viable locations for magnetic reconnection have not been formally assessed under fundamental plasma theory. Here we present an analytical model parametrizing typical steady-state conditions at Ganymede’s upstream magnetopause and evaluate magnetic reconnection onset conditions at the boundary. We find that the onset is satisfied where the adjacent magnetic fields are partially anti-parallel, which is the case across the entire magnetopause. This result is not impacted by variations of Ganymede’s position relative to the Jovian current sheet. The loose constraint on magnetic reconnection indicates the possibility of multiple X-lines consistent with MHD simulations. The reconnection electric field has magnitude ~3-6 mV/m and increases when Ganymede lies outside the current sheet, indicating a previously unconfirmed Jovian diurnal variation in reconnection rate. Understanding magnetic reconnection structure will improve our knowledge of plasma convection within Ganymede’s magnetosphere. Further model development may include dynamical effects, which will provide insights into Ganymede’s internal liquid ocean – a potential life source in the Solar System.