Mercury's Alfvén Wing Current System Under Sub‐Alfvénic Solar Wind Conditions: Insights From Global MHD Simulations

Abstract Mercury's proximity to the Sun results in the lowest average Alfvénic Mach number in the upstream solar wind compared to any other planet. Under extreme conditions, the upstream Alfvén speed can exceed the solar wind speed, resulting in a sub‐Alfvénic interaction in which standing Alfvén wings form. Previous studies suggest strong Alfvén wing formation requires a large obstacle conductance, yet estimates of Mercury's interior conductance remain comparatively small, raising questions about how strong Alfvénic interactions occur. Here, we investigate Mercury's Alfvén wing current system using global magnetohydrodynamic simulations with coupled planetary interior under varied sub‐Alfvénic solar wind conditions and interior conductances. Based on magnetic perturbations within the modeled Alfvén wings, we estimate that an effective magnetospheric conductance exceeds the relatively weak conductance associated with the planetary interior, increasing overall Alfvénic interaction strength. Additional current‐closure pathways provided by Mercury's intrinsic magnetosphere enhance the planet's effective conductance, strengthening Alfvén wing formation.