Dynamics of Ganymede's magnetopause: Intermittent reconnection under steady external conditions

Magnetic reconnection at the terrestrial magnetopause is frequently intermittent, leading to the formation of localized reconnected flux bundles referred to as flux transfer events (FTEs). It remains unclear whether the intermittency of the process is intrinsic or arises because of fluctuations of solar wind properties. Here we use Ganymede's magnetosphere, which is embedded in a background of field and plasma whose properties vary imperceptibly over time scales pertinent to plasma flow across the moon's magnetosphere, to demonstrate that reconnection is intrinsically intermittent. We run time‐dependent global magnetohydrodynamic (MHD) simulations that describe Ganymede's magnetospheric environment realistically and reproduce plasma and field measurements made on multiple Galileo passes by the moon with considerable fidelity. The simulations reveal that even under steady external conditions, dynamic variations associated with magnetic reconnection on time scales of the order of tens of seconds occur over a large region near the upstream magnetopause. The MHD simulations give direct evidence of magnetic reconnection at the magnetopause and reproduce the amplitude and spatial distribution of observed fluctuations of the magnetic field near boundary crossings. The consistency of data and simulations leads us to conclude that even under steady upstream conditions, upstream reconnection is intermittent. The bursty magnetopause structures at Ganymede and the FTEs identified at planetary magnetospheres (Mercury, Earth, and Jupiter) extend the parameter regime for analysis of intermittent magnetopause reconnection. We find that FTE recurrence times decrease with the scale length of the system.