Does Tribocharging Influence the Motion of Particles on Martian Slopes?

There are ongoing discussions if the slopes on Mars are as steep as on Earth or not. With this in mind, we are investigating angles of repose in laboratory experiments. In the particular series of experiments reported here, we study the influence of the low ambient pressure. We started by observing angles of repose for piles of different kinds of grains prepared under normal  conditions at 1 bar, representative of Earth. We then built piles of the same material at 3 mbar in the pressure range found on Mars. For some samples we observed a strong change, i.e. a large variation in slope angles and clumping at low pressure. We do not see this change e.g. for metallic particles. As previous work on generating piles under low pressure showed sparking, we speculate that the different behaviour can be attributed to tribocharging. This would make sense due to the reduced amount of water on the sample at low pressure, which makes the grains more insulating and prone to tribocharging. We currently set up charge measurments to verify this hypothesis. Triboelectric effects should influence particle motion on Martian slopes in this case much more than on Earth.