A statistical survey on the magnetic field distribution in Mercury's magnetotail current sheet based on MESSENGER observations

In this study, we use the magnetic field data measured by MESSENGER from 2011 to 2015 to survey the average magnetic field distribution in Mercury's magnetotail current sheet. It is found that the tail current sheet coincidently lies in the magnetic equator plane due to the ignorable dipole tilt angle (<3 degrees). The magnetic field B-z component is much larger than the B-y component at the current sheet center, which suggests that the field structure is almost vertical to the equatorial plane. In comparison with the region closer to Mercury (-1.5R(M)>X>2.ORM), at the distant region (-2.0R(M)>X>-2.5R(M)) the magnetic field strength B-min as well as the B-z component are weaker, B-y component is stronger, while the signature of negative B-z tends to appear there. Thus, the distant current sheet (-2.0R(M)>X>-2. 5R(M)) is more dynamic than the closer current sheet. The distributions of B-min as well as the B-z show evident dawn-dusk asymmetry, e. B-min and B-z are relatively weaker duskward within the azimuthal angle 1200-1900 where the data points of weaker B-z(B-z <5 nT) also show higher occurrence probability. In contrast, the strong By component (vertical bar By vertical bar>5 nT) at the current sheet tends to appear at the dawnward region (Y<0). In addition, the statistical study shows that the B-y component does not have a significant correlation with the B-y, component of interplanetary magnetic field. By comparison with the Earth's magnetotail current sheet, the mechanisms to control the dawn-dusk asymmetry of magnetic field at Mercury's tail current sheet are discussed.