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 ( similar to 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.