MESSENGER observations of Mercury's magnetosphere during northward IMF

[1] MESSENGER's January 14, 2008, flyby of Mercury has provided new observations of the planet's magnetosphere for northward interplanetary magnetic field (IMF). The dusk magnetopause was located inward from the mean magnetopause surface, possibly due to reduced tail magnetic flux content for IMF Bz > 0 and/or the pressure of planetary pickup ions as they respond to the dawnward – v × B electric field in the magnetosheath. Within the plasma sheet rotations of the magnetic field are observed consistent with, Kelvin–Helmholtz vortices ∼1 RM in diameter (RM is Mercury's radius). MESSENGER exited through a 1,000 km-wide boundary layer bordered by inner and outer current sheets that resemble rotational and tangential discontinuities, respectively. The total magnetic field change across this layer is consistent with the predicted solar wind ram pressure at Mercury during the MESSENGER flyby.