Dust transport and electric field distributions in planetary craters

Smooth deposits, termed ‘dust ponds’, were observed in the craters on Eros. Electrostatic dust transport has been suggested to contribute to the formation of these ponds. High energy electron fluxes incident upon craters at an angle can form an impact/shadow boundary in the crater, resulting in differential charging and the formation of intense localized electric fields. In the laboratory, we used electron fluxes with energies up to 90 eV to bombard an insulating half-pipe. An angle of incidence was chosen so that the impact occurred only on the farside of the slope and left the bottom and the nearside slope in electron shadow. Dust particles on the beam-illuminated slope moved down along the surface toward the bottom of the half-pipe and hopped to the bottom as well, while particles on the shadowed slope remained at rest. The outcome of these experiments critically depends on the ratio of the size of the half-pipe and the characteristic plasma shielding distance. When the radius of a crater is much larger than the Debye length, the plasma expands into the crater. In the opposite case, the plasma remains excluded from the crater. Hence, the electric field distribution in a crater can be very different depending on the size and shape of a crater and the properties of the plasma environment, resulting in different dust transport processes. In this paper, we will present both computer simulation and experimental results.