Ejecta Stratigraphy Modeling of the NASA/VIPER Exploration Zone at Mons Mouton Near the Lunar South Pole

Abstract

Permanently shadowed regions (PSRs) within some lunar polar craters host water ice and other volatiles delivered by sources such as asteroids, comets, interior degassing, and solar wind sputtering because of their frigid temperatures. However, over geological timescales, the abundance and spatial distribution of these ice deposits are disrupted by surface processes such as impact excavations, ejecta blanketing, and mass wasting, which cause them to be diluted and mixed with lunar regolith. To inspect their resource potential and to decode their origin and physical characteristics, NASA has planned the Volatiles Investigating Polar Exploration Rover (VIPER) to Mons Mouton near the Moon’s south pole in 2024. The rover will seek ice by exploring with a 1 m drilling instrument and an array of spectrometers. In this thesis, I characterize the ejecta stratigraphy produced by small, local impact craters around the VIPER exploration site to constrain the distribution of ice and regolith within the shallow subsurface. I constructed a Monte Carlo-based ejecta deposition model that simulated the layering of ejecta produced by craters bigger than 20 m in diameter and predicted that nearly 0.9 to 59 m thick ejecta covers VIPER’s primary mission area. I also determined the extent of PSRs that could host surface ice at the VIPER site by modeling long-term shadows using high-resolution topographic data. By analyzing the evolution of ejecta thickness as a function of surface age, I find that the upper 1 m of the crust, which is VIPER’s drilling depth, is covered by ejecta emplaced in the last ∼1 billion years. Freshly supplied volatiles will likely be present in the VIPER 1 m drill cores if they have endured the effect of impact mixing and space weathering processes since deposition.