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, https://doi.org/10.1029/2020je006790) 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 η varies with primary electron energy, which decreases with increasing energy. Our results also reveal η 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. Plain Language Summary Lunar surface is electrically charged to different degrees depending on the space environment of the Moon. Lunar surface charging is an important topic for robotic and human lunar exploration, as well as scientific observations from the surface. One of the quantities related to the lunar surface charging is the backscattering coefficient, which represents the probability that an incident electron is backscattered away from the lunar surface after impact as opposed to be absorbed by the surface. This study provides estimates of the electron backscattering probability with measurements from the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun spacecraft. We have determined the probability to be 0.1–0.3 at different electron energies. This is also affected by the magnetized environment at the Moon, causing some initially scattered electrons to return to the surface. The characterization of the backscattering coefficient not only gives insights into lunar surface charging and the lunar surface properties but could also be potentially applied to other airless bodies. Key Points We utilize the oxygen Auger electron peak to isolate cases of emitte