  Surfaces of planetary bodies can have strong electric fields, subjecting
conductive grains to repulsive electrostatic forces. This has been proposed as
mechanism to eject grains from the ground. To quantify this process, we study
mm-sized basalt aggregates consisting of micrometer constituents exposed to an
electric field in drop tower experiments. The dust aggregates acquire high
charges on sub-second timescales while sticking to the electrodes according to
the field polarity. Charging at the electrodes results in a repulsive (lifting)
force and continues until repulsion overcomes adhesion and particles are
lifted, moving towards the opposite electrode. Some aggregates remain attached,
which is consistent with a maximum charge limit being reached, providing an
electrostatic force too small to counteract adhesion. All observations are in
agreement with a model of moderately conductive grains with a small but varying
number of adhesive contacts to the electrodes. This supports the idea that on
planetary surfaces with atmospheres, electrostatic repulsion can significantly
contribute to airborne dust and sand, i.e. decrease the threshold wind speed
that is required for saltation and increase the particle flux as suggested
before.
