Photoemissivity is one of the fundamental properties of the lunar regolith. The photoelectric properties of the lunar surface are particularly relevant to the electrostatic environment on the moon's…

This federal contract award, valued at $307,219.95, was granted by the National Aeronautics and Space Administration (NASA) to the Regents of the University of California, doing business as the University of California, Berkeley. The contract is for research on the photoelectric properties of the lunar regolith and the lunar electrostatic environment. The research aims to answer key questions about the high-energy solar photon-driven photoelectric yield of the lunar surface and the temporal and spatial variability of the electrostatic environment on the sunlit lunar surface. The research will leverage data from NASA's Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission and the Solar Dynamics Observatory (SDO) mission. This contract does not have a set-aside designation, and the State of California Controller's Office is the parent organization of the University of California, Berkeley.

Photoemissivity is one of the fundamental properties of the lunar regolith. The photoelectric properties of the lunar surface are particularly relevant to the electrostatic environment on the moon's dayside, because the current balance of the emitted photoelectrons and incoming electrons is the primary factor controlling lunar surface charging. The resulting surface potential determines the dynamics of charged dust grains and ionized constituents of the tenuous lunar atmosphere. In particular, the high-energy part of the photoelectron spectrum is critical for determining surface potentials in low-plasma-density conditions (e.g., in the terrestrial magnetotail lobes). Despite its importance, the photoelectric yield of the lunar surface for high-energy (>20 EV) solar photons remains undetermined, limiting our ability to characterize and assess the electrostatic properties at various surface locations, including potential landing sites, in all ambient plasma conditions that the moon encounters. To improve our knowledge and understanding of regolith properties and the lunar electrostatic environment, we need to answer the following questions: (i) what are the photoelectric properties of the lunar regolith for high-energy solar photons? (II) what is the temporal and spatial variability of the electrostatic environment on the sunlit lunar surface in varying solar and plasma conditions?, and (III) how does the lunar electrostatic environment influence lunar exospheric pickup ions and surface weathering? We aim to answer these questions by combining publicly available plasma measurements from the acceleration, reconnection, turbulence, and electrodynamics of the moon's interaction with the sun (artemis) mission and solar extreme ultraviolet (EUV) fluxes from the solar dynamics observatory (SDO) mission and the observation-based flare irradiance spectral model (fism). The dual-probe artemis mission conducts comprehensive plasma and electromagnetic field measurements with spacecraft potential information, enabling observations of the high-energy distribution of lunar photoelectrons escaping from the sunlit lunar surface along the magnetic field line with clear separation of lunar photoelectron spectra from spacecraft photoelectron contamination. Combination of clean, accurate lunar photoelectron spectra obtained by artemis with simultaneous, direct EUV measurements by SDO, which can be complemented by fism for