  Dust emission mechanisms as one aspect of wind-driven particle motion on
planetary surfaces are still poorly understood. The microphysics is important
though as it determines dust sizes and morphologies which set sedimentation
speeds and optical properties. We consider the effects of tribocharging in this
context as grains in wind driven granular matter charge significantly. This
leads to large electric fields above the granular bed. Airborne dielectric
grains are polarized in these electric fields, which leads to attractive forces
between grains. To simulate aggregation under these conditions we carried out
drop tower experiments using tracer particles, mimicking the gas coupling
behavior of small dust grains in terms of high surface to mass ratios and
efficient gas drag. Under microgravity, the particles are released into an
observation chamber in which an alternating electric field up to 80 kV/m is
applied. Without electric field no aggregation can be observed on timescales of
seconds. However, polarization instantly leads to aggregation of particles when
the field is switched on and long chains aligned to the electric field form.
Scaled to dust entrained into planetary atmospheres, fine and coarse grain
fractions might readily form aggregates after being liberated. Under certain
natural conditions, aggregates might therefore start chain-like or at least a
chain-like appearance is favored. If atmospheric influences on their stability
are small, aerodynamic and optical properties might depend on this.
