Characteristics of Lunar Surface Electrons Inferred From ARTEMIS Observations: 1. Backscattered Electrons

Lunar surface charging is a scientifically and practically important topic at the Moon that is largely determined by the electron currents near the surface. Among those electron populations, lunar photoelectrons (PHE) and backscattered electrons (BSE) produced by incident electrons that make up the high-energy tail of lunar emitted electrons are not well characterized yet. Recently, Xu et al. (2021, ) reported oxygen Auger electron observations at the Moon by the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun spacecraft, which provides a unique feature to identify lunar photoelectrons. We utilize this feature to isolate cases of emitted electrons dominated by BSE over PHE. With selected BSE cases, we characterize how the backscattering coefficient eta varies with primary electron energy, which decreases with increasing energy. Our results also reveal eta to be dependent on the magnetic dip angle, as a fraction of BSE re-impact the surface in a magnetized environment. The characterization of the backscattering coefficient not only gives insights into the lunar surface properties and lunar surface charging but could also be potentially applied to other airless bodies.