Surface Processes on Airless Planetary Bodies: Quantifying the Effects of Regolith Mixing on the Lunar South Pole and Ejecta Deposition on Ceres

Abstract

In airless planetary bodies, impact cratering is the dominant geologic processes that modifies and evolves their surface. Therefore, studying impact craters on airless planetary bodies contributes to a better understanding of how surface materials in our solar system have evolved and are evolving throughout time. Water is an important material in our solar system because it plays a critical role in life. On airless planetary bodies, such as the Moon and Ceres, water ice is observed in permanently shadowed polar regions. One of the major sources for water in our solar system has been asteroids and comets, which deliver water during impact cratering events. However, the relationship between water and impacts in airless planetary bodies remains poorly understood. Thus, this study aims to quantitatively constrain the relationship between water and impacts and their implications to impact-related deposits. Through measurements of simple craters within and outside large complex crater systems, this research seeks to quantify two impact processes: regolith mixing by breccia lensing; and ejecta blanketing. First, on the lunar south pole, Haworth, Shoemaker, and Faustini, three ancient complex craters, which host water ice in their floors, were selected to investigate the role of regolith mixing to water concentrations at depth. And second, on Ceres, five complex craters were selected to quantify their ejecta deposit thicknesses to investigate the influence of water towards ejecta deposition. On lunar south pole, using crater distributions and regolith mixing modeling, crater floor subsurface water concentrations range from ∼0.1 to 0.2 wt. % at ∼11 to ∼40 m, implying that regolith mixing leads to water removal rather than preservation at depth. On Ceres, based on ejecta scaling relationships and a covariance ellipse approach, ejecta thicknesses range from ∼3 to 73 m and ∼96 to 223 m around complex craters and at their rim crest localities, respectively. Fluidization from subsurface water ice meltwater causes thin ejecta deposits on Ceres. Research on the Moon and Ceres are reported herein as separate chapters in the present dissertation, and in both instances, these investigations provide new constraints for better understanding of the evolution and role of water beyond the Earth.