Dynamics of Electrostatically Lofted Dust Above Airless Bodies

Abstract:

Since the first observation of the lunar horizon glow in the 1960s, electrostatic dust charging and lofting has been postulated and studied in order to explain related observations on the surfaces of the Moon and other airless bodies. This electrostatic dust phenomenon may have important implications for the evolution of the surface properties of these airless bodies.

A recently proposed “patched charge model” describes the charging and lofting of dust grains exposed to ultraviolet (UV) irradiation via the accumulation of large charges inside microcavities in the regolith. This model was verified with several lab experiments that measured and found a relationship between initial charges and launch velocities of lofted dust grains in a variety of sizes. Contrary to previous expectations for a photoemitted regolith surface, the charges on lofted grains are negative.

Solar UV irradiation of the surface of an airless body causes photoemission, resulting in an electric field called a photoelectron sheath above the surface. The electrostatic interaction of dust particles with this sheath as well as the solar wind determines the fate of lofted dust grains, including possible dust levitation.

In this study, we present new results of the dynamics of lofted dust grains based on the patched charge model as they interact with the gravitational and electric fields on airless bodies of a variety of sizes from the Moon to small asteroids. We account for charging effects of the grains in the course of flight due to UV radiation, solar wind electrons and ions, the photoelectron sheath, and the production of secondary electrons. We show that on larger bodies like the Moon, gravity mainly determines the lofting height while on smaller bodies like asteroids, electrodynamic processes play an increasingly significant role in dust dynamics. Our results provide new insights into dust dynamics on airless bodies across the solar system.