<b>Exploring the Surface Processing of Apollo Apollo 17 Lunar Soils via Transmission Electron Microscopy</b>

<p dir="ltr">Space weathering is a process by which regolith on the surfaces of airless bodies, such as the Moon, is altered by its exposure to interplanetary space. Space weathering is driven by two primary processes: (1) micrometeoroid impacts, and (2) solar wind irradiation. Both of these processes alter the regolith on these bodies both chemically and microstructurally. Micrometeoroid impacts generate impact melt and vapor, and energetic particles from the solar wind and solar flares damage the microstructure of grains in surface regolith. Both of these processes can contribute to the production of metallic iron nanoparticles, known as nanophase iron (npFe). Space weathering was first characterized in lunar samples returned by the Apollo program, and in the subsequent decades extensive laboratory analyses have been performed to understand and characterize the properties of space weathering on the lunar surface.</p><p dir="ltr">In the analysis of lunar samples, the transmission electron microscope (TEM) provides an opportunity to characterize microstructural and chemical characteristics of space weathering down to the atomic scale. This technique has been applied to the study of impact melts and vapor deposits, the extent of damage caused from solar irradiation, and to understanding the chemical and microstructural evolution of nanophase iron particles. TEM and its associated analytical applications are uniquely suited to the study of space weathering features, and so I employ this technique throughout my dissertation.</p><p dir="ltr">This dissertation is divided into five chapters. Chapter 1 is an overview of space weathering on the Moon, including discussion of mechanisms driving this surface process and their resultant microstructural and chemical products. It also discusses the geological context, collection, and curatorial processing of Apollo 17 core sample 73001/2 and associated lunar regolith samples from the same mission that are analyzed in this study. Chapter 2 introduces the functions of the TEM and associated analytical techniques that will be used in this work. Chapter 3 is a study by which the proportion of space weathered material and analysis of exposure ages derived from irradiation damage signatures in grains from 73001/2 are used to constrain our understanding of regolith mixing and overturn. Chapter 4 builds upon Chapter 3 by conducting a similar analysis applied to scoop samples with unique exposure histories to better understand the geologic history of the Apollo 17 field site, and to explore the relationship between exposure age distribution and other maturity indices. Chapter 5 leverages the unique features of the core sample to perform an analysis of the oxidation state of nanophase iron particles in relation to stratigraphic depth in order to provide insight into potential mechanisms driving nanoparticle evolution, and to constrain a relationship between oxidation state and particle morphology.</p>