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In microgravity experiments, dielectric spherical glass grains of 225 μm radius with electrical charges between 10 5 e and 10 7 e collide with a metal wall. Collision velocities range from about 0.01 m/s up to 0.2 m/s. Grains rebound from the wall down to a threshold impact velocity below which particles stick. This threshold velocity for sticking increases linearly from below 0.01 m/s to 0.15m/s with increasing charge on the grains. This can be explained by non-homogeneous surface charges on the grains and mirror charges on the metal wall. The Coulomb attraction boosts the grain speed just prior to impact. This increases the energy dissipated upon impact, and grains can no longer escape the Coulomb field of the mirror charge if they are too slow. For rebounding particles, the final boost decreases the measurable, effective coefficient of restitution and induces a wide spread.

In parabolic flight experiments we studied the wind induced erosion of granular beds composed of spherical glass beads at low gravity and low ambient pressure. Varying g-levels were set by centrifugal forces. Expanding existing parameter sets to a pressure range between p = 300 − 1200 Pa and to g-levels of g = 1.1 − 2.2 m s −2 erosion thresholds are still consistent with the existing model for wind erosion on planetary surfaces by Shao & Lu (2000). These parameters were the lowest values that could technically be reached by the experiment. The experiments decrease the necessary range of extrapolation of erosion thresholds from verified to currently still unknown values at the conditions of planetesimals in protoplanetary discs. We apply our results to the stability of planetesimals. In inner regions of protoplanetary discs, pebble pile planetesimals below a certain size are not stable but will be disassembled by a head wind.

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We developed an experiment to study different aspects of granular matter under microgravity. The 1.5U small experiment was carried out on the International Space Station. About 3500 almost identical spherical glass particles with 856 µm diameter were placed in a container of 50 by 50 mm cross section. Adjusting the height between 5 and 50 mm, the filling factor can be varied. The sample was vibrated with different frequencies and amplitudes. The majority of the data are video images of the particles' motion. Here, we give a first overview of the general setup and a first qualitative account of different phenomena observed in about 700 experiment runs. These phenomena include collisional cooling, collective motion via gas-cluster coupling, and the influence of electrostatic forces on particle-particle interactions.