Mercury's Field-Aligned Currents: Perspectives From Hybrid Simulations

Previous studies suggested that Mercury's magnetosphere could possess Earth-like field-aligned currents (FACs) despite the absence of an ionosphere. However, due to the limited coverage of spacecraft observations, our understanding of Mercury's FACs is scarce. Here, we employed Amitis, a hybrid-kinetic plasma model, to investigate the establishment and global pattern of Mercury's FACs. The responses of Mercury's FACs to various interior conductivity profiles and different orientations of the upstream interplanetary magnetic field (IMF) were simulated. It has been shown that the profile of a less resistive upper layer and a conducting core favors the establishment of FACs. Three types of large-scale FACs (Region 1-like, Region 2-like and NBZ-like FACs) are shown in simulations. Comparison with previous observations suggests that Mercury's effective conductance for closing R1-like FACs is ∼2.4–3.4 S. The influence of IMF orientation on FACs is similar to that observed in Earth's magnetosphere, but the response of the R2-like FACs to the IMF orientation is different.