Complex electric fields near the lunar terminator: The near-surface wake and accelerated dust

Abstract

The lunar near-surface electric field in the vicinity of the terminator is very complex, with a surface polarity change from dayside-positive to nightside-negative potentials and the formation of intensely negative potentials due to the low plasma density and increased temperatures in the trailing lunar wake region. Presented is a preliminary map of the terminator near-surface E-field magnitude and a discussion of dust dynamics in this E-field structure, with intense vertical fields tending to give rise to vertically directed dust trajectories (aligned with the surface normal). Application of this process of wake-generated surface E-fields and dust to the more complicated topography at the lunar landing site of Apollo 17 is then used to explain the detection of fast moving (∼500 m/sec) but nightside-directed dust in the region. We suggest that local solar wind orographic effects occurring at lunar sunrise/sunset can create a plasma void on the anti-sunward side of obstructing features and associated wake-generated surface E-fields can then be the source of the nightside-directed grains.