Lunar Potential Determination Using Apollo-Ear Data and Modern Measurements and Models

Since the Apollo era the electric potential of the Moon has been a subject of great interest and debate. Deployed on the surface by three Apollo missions (Apollo 12, 14 and 15), the Suprathermal Ion Detector Experiments (SIDE) were used to infer a sunlit surface potential of about +10 V from the energy spectra of lunar ionospheric thermal ions accelerated toward the Moon. More recently, electron distributions measured from orbit by the Lunar Prospector Electron Reflectometer (LP ER) have been used to infer negative lunar surface potentials, primarily in shadow. We will present initial results from a study to combine lunar surface potential measurements from both SIDE and LP ER to calibrate an advanced lunar surface charging model that includes electric currents from the plasma environment, photoelectron and secondary electron emission from the surface, as well as the effects of the wake formed downstream by the solar wind-lunar interaction.