Analyzing the Moon’s Exosphere with Seven Years of Far-Ultraviolet LRO-LAMP Spectra

The lunar exosphere, a tenuous environment crucial for understanding surface-exosphere interactions, is investigated using extended Far-Ultraviolet (FUV) spectroscopy from the Lunar Reconnaissance Orbiter’s (LRO) Lyman Alpha Mapping Project (LAMP). Leveraging seven years of continuous dawn/dusk orbital data, doubling the previous reported (Cook et al., Icarus, 2013) 3.5-year dataset, we aim to improve constraints on exospheric species, their densities, and temporal variability. Our methodology involves detailed evaluation of LAMP spectra (57-196 nm) during twilight passes, employing robust background removal to isolate faint exospheric signals from reflected UV starlight and earthshine. We focus on identifying emission lines of neutral atomic species, with helium being a prominent detection. This study extends prior work by applying the same twilight observation technique to a significantly longer temporal baseline, enhancing the signal-to-noise ratio for spectral line detections or upper limits. Analyzing this extended dataset allows for a more precise determination of species abundances and the potential identification of fainter constituents. By constraining temporal variations in these densities, we further explore the source mechanisms (e.g., sputtering, desorption, outgassing) and loss processes governing the lunar exosphere.