Examining the Ballistic Transport of Sulfur-Bearing Volatile Species in the Lunar Exosphere

Although Earth’s Moon lacks a collisional atmosphere, it is known to possess a surface-bounded collisionless exosphere populated by volatile species undergoing thermally-driven ballistic jumps across the surface. Previous models of the lunar exosphere have focused primarily on atomic species (e.g. H, Ar, etc.), with water, hydroxyl (OH), and H₂ being the only molecular species that have received significant attention.

However, these are not the only volatile molecular species that exist on the Moon. The LCROSS impactor uncovered a diverse population of volatile species within one of the Moon’s polar permanently-shadowed regions, of which water was the most abundant. Here, we model the exospheric ballistic transport of two sulfur bearing species (H₂S and SO₂), that were measured in the LCROSS impact plume at abundances of 16.75% and 3.17% relative to water, respectively. As a key component in our model, we use molecular dynamics simulations to determine the surface binding energy distributions of these two species on lunar-like surfaces.