Neutron spectroscopy is used to determine bulk water abundances in the near surface of planetary bodies. The Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) rover, Curiosity, is able to determine the depth distribution of water and neutron absorbers in the top ~50 cm of the subsurface. In this dissertation, I focus on answering significant geologic questions by interpreting DAN results in the geologic context provided by other MSL and orbital datasets. This approach enabled me to investigate significant outstanding questions in Gale crater geology, with implications for the evolution and habitability of Mars.I mapped an extensive silicic volcaniclastic layer in the subsurface, the first identified and mapped on Mars. This layer served as a silica source for other silica-rich features. But unlike those features, this layer contains abundant rhyolitic glass, indicating an evolved volcanic origin. Similar material on Earth is produced by plate tectonics, so this layer has important implications for the evolution of Mars, which has no evidence of plate tectonics. One of the primary motivations for exploring Gale crater is a distinct clay mineral signature from orbital data of the Compact Reconnaissance Imaging Spectrometer at Mars (CRISM), which has also identified a corresponding hydration signature. I compared DAN and CRISM hydration results and found that CRISM hydration results are biased by the presence of regolith, indicating that this regolith is either more hydrated or has a different grain size texture than bedrock. Clay minerals are primary binding sites for organics on Earth, and most organic-mineral binding mechanisms involve either water or hydroxyl. This makes hydrated clays the most efficient hosts for organic preservation, but clays are normally dehydrated when measured by MSL. However, my DAN-derived water abundances are greater in the most clay-rich unit of Gale crater, suggesting that clay minerals may be hydrated in the subsurface. I developed a new amorphous component analysis method that simultaneously constrains clay mineral hydration and abundances of various hydrated amorphous phases. I found a strong correlation between “excess” water and smectites (expandable clay minerals), indicating that these clay minerals are hydrated in the subsurface.

Impact cratering and volcanism are two fundamental processes that alter the surfaces of the terrestrial planets. Though well studied through laboratory experiments and terrestrial analogs, many questions remain regarding how these processes operate across the Solar System. Little is known about the formation of large impact basins (>300 km in diameter) and the degree to which they modify planetary surfaces. On the Moon, large impact basins dominate the terrain and are relatively well preserved. Because the lunar geologic timescale is largely derived from basin stratigraphic relations, it is crucial that we are able to identify and characterize materials emplaced as a result of the formation of the basins, such as light plains. Using high-resolution images under consistent illumination conditions and topography from the Lunar Reconnaissance Orbiter Camera (LROC), a new global map of light plains is presented at an unprecedented scale, revealing critical details of lunar stratigraphy and providing insight into the erosive power of large impacts. This work demonstrates that large basins significantly alter the lunar surface out to at least 4 radii from the rim, two times farther than previously thought. Further, the effect of pre-existing topography on the degradation of impact craters is unclear, despite their use in the age dating of surfaces. Crater measurements made over large regions of consistent coverage using LROC images and slopes derived from LROC topography show that pre-existing topography affects crater abundances and absolute model ages for craters up to at least 4 km in diameter.

On Mars, small volcanic edifices can provide valuable insight into the evolution of the crust and interior, but a lack of superposed craters and heavy mantling by dust make them difficult to age date. On Earth, morphometry can be used to determine the ages of cinder cone volcanoes in the absence of dated samples. Comparisons of high-resolution topography from the Context Imager (CTX) and a two-dimensional nonlinear diffusion model show that the forms observed on Mars could have been created through Earth-like processes, and with future work, it may be possible to derive an age estimate for these features in the absence of superposed craters or samples.

Guided by the Obama administration, NASA has begun developing commercial launch capabilities. For both cargo and crew delivery to the International Space Station, NASA has selected companies to build and operate the vehicles at a fixed price. Alexander McDonald suggests that this continues a trend in space exploration established by large observatory projects, and that the Apollo-era style of funding and operation was a historical anomaly. This paper attempts to discover if historical analog can support or weaken this thesis. The analogs chosen are two episodes in the history of terrestrial exploration: the experience of the Spanish and British empires in North America. These are compared to the history of space exploration up until today, focusing on how the role of private enterprise has changed in each instance. While the analogies between historical episodes are weak in a few areas, they do possess a common narrative concerning the shifting balance between private and government interests. This narrative supports McDonald's thesis, and shows that NASA's current policy anticipates an expected transition towards a private-public hybrid model of exploration and expansion.