New Constraints on the Escape of Sodium and Potassium From the Moon

Recent measurements and models of the lunar alkali exosphere enable us to better understand the effect of the Sun on the escape of the Moon's weak atmosphere. Sodium and potassium gases are important tracers of microphysical processes on the Moon because they can be easily observed from Earth as well as from lunar orbiters. Comparing exospheric transport models to recent high-resolution spectroscopic measurements from Earth , we may significantly constrain the velocity distribution of alkalis liberated from the lunar surface and the surface release processes. We find that a systematic increase in Doppler width towards full Moon phases is consistent with photon stimulated desorption with a high speed tail. Additionally, residual Doppler widths correlate to the solar wind flux measured by ARTEMIS, a finding that suggests non-negligible contributions by sputtering.