Mercury's Cross-tail Current Sheet: Structure, X-line Location and Stress Balance

The structure, X-line location and magnetohydrodynamics (MHD) stress balance of Mercury's magnetotail were examined between -2.6 < XMSM < -1.4 RM using MESSENGER measurements observed from 319 central plasma sheet (CPS) crossings. The mean plasma β in the CPS calculated from MESSENGER data is ~ 6. The CPS magnetic field was southward (i.e., tailward of X-line) ~ 2 – 18% of the time. Extrapolation of downtail variations in BZ indicates an average X-line location at -3 RM. Modelling of magnetic field measurements produced a cross-tail current sheet (CS) thickness, current density and inner CS edge location of 0.39 RM, 92 nA/m2 and -1.22 RM, respectively. Application of MHD stress balance suggests that heavy planetary ions may be important in maintaining stress balance within Mercury's CPS. Qualitative similarities between Mercury's and Earth's magnetotail are remarkable given the differences in upstream conditions, internal plasma composition, finite gyro-radius scaling, and Mercury's lack of ionosphere.