Laboratory measurements of initial launch velocities of electrostatically lofted dust on airless planetary bodies

Electrostatic dust lofting may play an important role in surface evolution of airless bodies as indicated from a number of unexplained observations, including the lunar horizon glow and dust ponding on asteroids, for example. The initial launch velocity of a charged dust particle determines its range of motion, hence it is a critical quantity to assess the dynamics of electrostatic dust transport. Here we report on laboratory measurements of the launch velocity of electrostatically lofted dust and its relationship with the dust size. For irregularly-shaped dust, similar-sized particles show a large velocity dispersion, indicating a large variation in the inter-particle cohesive force. The maximum launch velocity is shown to decrease with the increase in the dust radius and it is on the order of ~0.7 m/s for 15 μm radius particles. Derived from the patched charge model (Wang et al., 2016a. Geophys. Res. Lett. 43, 6103–6110), the theoretical expectation of an inverse velocity-size relationship of lofted dust is shown to be consistent with the maximum launch velocity measurements. The dust shape is found to have a significant effect on the lofting process, showing that irregularly-shaped particles are lofted with much larger velocities than spherical particles. The initial launch angle relative to the surface shows a broad distribution.