Ranking Adhesion Forces for Charged Lunar Dust Particles on Conducting Surfaces

Both image-charge forces and surface-energy (i.e. van der Waals) interactions contribute to the adhesion of charged dust particles on conducting surfaces. In-situ lunar regolith is charged (positively on the sunlit side of the moon, from UV photo-ionization, and negatively on the dark side, from electrons in the solar wind). Furthermore, mechanically disturbed regolith can attain a triboelectric charge which is different than its charge-state before the disturbance. The expected size dependence of the charge-to-mass ratio for fine lunar particulates differs depending on which mechanism caused the charge. Based on current theories and measurements, it is expected that, as the size of dust particles decreases, the adhesion forces acting on particles in contact with conducting surfaces will be dominated by van der Waals' forces, or by image-charge forces, depending on whether the fine particles attained their charge from solar sources (i.e., photo ionization or solar wind) or from triboelectric (i.e., mechanical) means, respectively. At present we have insufficient information on the size dependence of charge-to-mass ratios of insitu or mechanically disturbed lunar regolith particles to resolve this uncertainty.