Juno Magnetometer Observations at Ganymede: Comparisons With a Global Hybrid Simulation and Indications of Magnetopause Reconnection

Juno's flyby of Ganymede on 7 June 2021, provides a unique opportunity to explore the moon's magnetosphere. By means of Magnetometer (MAG) observations and a hybrid numerical simulation, we provide a global description of this environment and analyze the upstream magnetopause in detail. In particular, LATMOS Hybrid Simulation results suggest Juno observed open (one foot‐point connected to Ganymede, the other to Jupiter) and closed magnetic field lines along its trajectory. Additionally, we determine that the upstream magnetopause location and orientation seen by Juno MAG are consistent with previous Galileo observations. We observe a non‐zero normal component of the magnetic field across the magnetopause, along with flux rope structures embedded within the boundary's current sheet. Both signatures are strong indicators that magnetic reconnection was occurring along Ganymede's magnetopause. Based on this crossing, we calculate a shear angle of ∼78° across the magnetopause, with a dimensionless reconnection rate of ∼0.12.