Transport and distribution of sodium ions in Mercury’s magnetosphere: results from multi-fluid MHD simulations

In the absence of a substantial ionosphere, solar wind protons dominate the plasma content within Mercury’s magnetosphere. However, Mercury is surrounded by a tenuous neutral exosphere composed primarily of sodium atoms, which can be continuously ionized. The production of sodium ions is concentrated on the dayside, and these ions can subsequently be transported to the magnetotail and flanks. MESSENGER spacecraft observations revealed dawn-dusk asymmetric distributions of sodium ions Na⁺. In this study, we present a two-fluid MHD model that is coupled with an empirical sodium exosphere profile to investigate the circulation, distribution, and influence of Na⁺ on global magnetospheric convection. Our findings indicate that the observed dawn-dusk asymmetries in Na⁺ distributions are driven by the separation of H⁺ and Na⁺ flows, with the Hall-driven global convection preferentially transporting Na⁺ ions to the morning sector.