Observations of Current Sheets Passing Through the Near Lunar Wake

Abstract:

Two reconnection exhausts were detected by one of the dual ARTEMIS orbiters in the solar wind near the Moon. Almost meanwhile, the other ARTEMIS orbiter encountered the two corresponding (to the exhausts) current sheets that show no reconnection signals at the relatively central and marginal locations in the near lunar wake. In the ``Margin Event", a strong magnetic enhancement in the normal direction has been found peaking near the neutral line. In the ``Center Event", the current sheet was significantly broadened in thickness. The rotations of magnetic field direction of the two current sheets became more smooth than those of the exhausts. It is the dropout currents which cannot penetrate into the near wake that mainly caused these observational magnetic features. Such magnetic configuration is very similar to the magnetic geometry between two anti-polarity permanent magnets parallel to each other in non conducting context. The essential reason is that the extremely low density plasma in the near wake can no longer carry as strong currents as in the solar wind to support the curl of the magnetic fields.