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

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.