The Magnetic Field Structure of Mercury's Magnetotail

Abstract

AbstractIn this study, we use the magnetic field data measured by MErcury Surface, Space ENvironment, GEochemistry, and Ranging from 2011 to 2015 to investigate the average magnetic field morphology of Mercury's magnetotail in the down tail 0–3 RM (RM = 2,440 km, Mercury's radius). It is found that Mercury has a terrestrial‐like magnetotail; the magnetic field structure beyond 1.5 RM down tail is stretched significantly with typical lobe field 50 nT. A cross‐tail current sheet separating the antiparallel field lines of lobes is present in the equatorial plane. The magnetotail width in north‐south direction is about 5 RM, while the transverse width is about 4 RM. Thus, the magnetotail shows elongation along the north‐south direction. At the cross‐tail current sheet center, the normal component of magnetic field (10–20 nT) is much larger than the cross‐tail component. The lobe‐field‐aligned component of magnetic field over current sheet can be well fitted by Harris sheet model. The curvature radius of field lines at sheet center usually reaches a minimum around midnight (100–200 km) with stronger current density (40–50 nA/m2), while the curvature radius increases toward both flanks (400–600 km) with the decreased current density (about 20 nA/m2). The half‐thickness of current sheet around midnight is about 0.25 RM or 600 km, and the inner edge of current sheet is located at the down tail about 1.5 RM. Our results about the field structure in the near Mercury's tail show an evident dawn‐dusk asymmetry as that found in the Earth's magnetotail, but reasons should be different. Possible reasons are discussed.