North-South Plasma Asymmetry Across Mercury's Near-Tail Current Sheet

Among nearly 300 near-Mercury tail current sheet crossings performed by the MESSENGER spacecraft, we identified 37 traversals of an asymmetric current sheet, wherein the lobe densities on opposite sides differ by a factor of three or more. These asymmetric current sheet crossings primarily occur on the dawnside. A global magnetohydrodynamic (MHD) simulation was found to be in excellent agreement with the observations. The results suggest that the north-south density asymmetry is caused by solar wind entering via an upstream-connected window in one hemisphere. Furthermore, the Parker spiral interplanetary magnetic field (IMF) controls the near-tail density asymmetries, whereas Mercury's offset dipole magnetic field controls those in mid- or distant-tail regions. We propose that hemispheric asymmetries in Mercury's magnetospheric convection occur under strong IMF conditions.