Charging and dynamics of dust particles in lunar photoelectron sheath

Sunlight scattering from electrostatically charged floating particles is considered accountable for the lunar twilight observations of horizon glow and streamers. In this work, the dynamics of the fine charged particles within the photoelectron sheath over the sunlit lunar surface has been investigated. Accounting for the influence of solar radiation, solar wind plasma, and lunar gravity, the present transport model consistently takes account of the coexisting phenomenon of particle charging, and characteristic photoelectron sheath screening in deriving the vertical motion of the particle. As novel features, half Fermi-Dirac statistics of the photoelectron velocity in determining the electron population and the sheath structure through the Poisson equation, and anisotropic photoelectron flux in evaluating the particle charge as it traverses through the sheath, have adequately been included in the analysis. In this framework, the electrostatic sheath features are observed to dominate over the lunar gravity in determining the dynamics of smaller (nanometer) size grains; for instance, similar to 10nm sized particles detached from the lunar regolith with a finite velocity are shown to loft up to the kilometer altitude. Depending on the initial particle velocity and size, a parametric regime defining the particle hopping over the lunar surface has been identified.