<p>  </p> <p>Though we cannot directly characterize the internal structure of Pluto, its interior can be probed remotely by observing its response to impact-induced deformation. The formation and evolution of giant impact basins like Sputnik Planitia, Pluto’s massive 1200 x 1400-km-diameter impact basin, is a unique geologic process that links the dwarf planet’s interior structure to the basin’s morphology and overall longevity. Its large size, location, and relationship to tectonic features has led researchers to suggest that Sputnik Planitia preserves evidence of a large subsurface ocean, while possible antipodal features observed on Pluto’s far side raise questions of how stress waves from impact may have traveled through Pluto’s interior, which remains somewhat unconstrained. In this dissertation, I strive to understand the relationship between the formation and evolution of Sputnik Planitia and the thermal and mechanical structure of Pluto at a variety of scales. The years following New Horizons’ flyby of the Pluto system in 2015 have yielded more questions than answers about the state of Pluto’s interior, including the thickness and thermal structure of its ice shell, the possible presence of a liquid water ocean, and the composition of its rocky core. I use impact simulations to reproduce the unique physics associated with impact cratering and further investigate which internal structures are consistent with the cratering record, as well as finite element models to explore the postimpact evolution of Pluto’s largest impact basin and probe the mechanical and thermal structure of the ice shell in more detail. With these tools, I show that the formation and evolution of Sputnik Planitia is consistent with the presence of a hydrated core and thick subsurface ocean in Pluto’s interior. The results of this dissertation contribute to understanding the origin, evolution, and interior of Pluto as well as other icy moons, ocean worlds, and large Kuiper Belt Objects in our solar system, and has direct implications for future exploration of other such worlds in our solar system.</p>

<p>While hypervelocity impacts are ubiquitous throughout the solar system and have received decades  of  research,  the dynamic  fragmentation that  occurs  during an impact has received relatively little attention. This is made more troublesome by the fact that, by volume, more material in the target is altered by the tensile stresses of the rarefaction wave that relieves the pressure of the shock wave, compared to the amount excavated by the impact itself. This tensionally affected material  can  include  Grady-Kippfragments,  fragments  of  material  that  were  broken  apart according to a dynamic fragmentation model developed by Grady and Kipp in 1980. By using their model and inserting it into the Eulerian hydrocode iSALE, we have been able to examine the role tensile stressesand dynamic fragmentation play in hypervelocity impacts. We started by finding the limits on Grady-Kipp fragmentation on an already well studied surface, the Moon. We found that fragment sizes are weakly dependent on impactor size and impact velocity. For impactors 1 km in diameter or smaller, a hemispherical zone centered on the point of impact contains meter‐scale fragments. For an impactor 1 km in diameter this zone extends to depths of 20 km. At larger impactor  sizes,  overburden  pressure  inhibits  fragmentation  and  only  a  near‐surface  zone  is fragmented. For a 10‐km‐diameter impactor, this surface zone extends to a depthof ~20 km and lateral distances ~300 km from the point of impact. This suggests that impactors from 1 to 10 km in diameter can efficiently fragment the entire lunar crust to depths of ~20 km, implying that much of the modern day megaregolith can be created by single impacts rather than by multiple large impact events.</p> <p>With the extent of in-situ fragmentation examined we turned ourattention to getting our dynamic fragmentation code to run smoothly with iSALE’s PorTens. PorTens is a change made to iSALE to allow for pore space creation in material undergoing tensile stresses and pressures in order to keep thermodynamic consistency. Importantly, wefound that when the two routines are combined, porosity increases substantially, and that the large basins currently observed on the Moon’s surface are likely most responsible for the high porosity detected by the Gravity Recovery and Interior Laboratory (GRAIL) mission. Additionally, we discovered that deep lying porosity seems to be additive, suggesting that even without the influence of the largest impactors it is possible for porosity to increase over time. The final, and possibly most consequential conclusion from this work is the ability of tensile stresses and pressures can create potential sitesof refugia for early life that may have existed on early Earth or possibly Mars.</p> <p>Our final dive into hypervelocity impacts focuses on modeling fragments of ejecta. To study this, we have restructured the original fragmentation code substantially. Because most of the damage occurring in the ejecta is done in shear, our previously used Grady-Kipp implementation is not able to provide any useful data, without first making some necessary changes. Much of shear stresses occurring during the passage of a shockwave is accommodated by ductile deformation. Thus, we allow tensile damage to accumulate independently of any calculated shear damage. This simple assumption allows us to track fragment size within ejecta curtains.We then present the results of fragment size vs velocity for different sized impactors.</p> <p><br></p>

<p>The <i>Curiosity</i> and <i>Perseverance</i> rovers have both found overwhelming evidence of a long-lived history of complex rock-water interactions on Mars. Understanding how the mineralogy of these deposits is related to depositional and diagenetic environments is critical for evaluating past habitable environments and guiding the search for signs of life with the <i>Curiosity</i> and <i>Perseverance</i> rovers. However, the chemistry and timing of these aqueous environments are poorly constrained. In particular, it is unclear which secondary minerals in the rock record formed in primary lacustrine vs. later diagenetic events. Understanding the origin of alteration minerals is crucial for studying habitability because they provide constraints on the timing and types of environments that existed. The goal of my thesis research is to better constrain the history of diagenetic processes in Gale and Jezero craters using the morphology, sedimentology, and mineralogy of features from rover and orbiter observations and comparisons to Earth analogs to understand their formation mechanisms. This research contributes to building a framework of the history of water in Gale and Jezero craters and will help us better understand past climate, habitability, and sources of water on Mars.</p><p>The <i>Curiosity</i> rover on the Mars Science Laboratory (MSL) mission has found extensive evidence that Gale crater once hosted a habitable lacustrine environment; however, there are remaining questions about the chemistry and duration of the lake and the nature of the climate at the time. In Chapter 2 of this thesis, I use Mastcam multispectral data to investigate the mineralogy of the Sutton Island member of the Murray formation, a part of the basal layers of Mt. Sharp, which consists of heterolithic mudstone and sandstone that are distinct from the finely laminated mudstones that dominate much of the Murray. Sutton Island includes at least one instance of desiccation cracks, indicative of subaerial exposure, and uniquely irregular diagenetic features that may be related to local bedrock permeability. These features suggest that Sutton Island experienced a complex history of deposition and diagenesis which may be crucial for understanding changing water-rock interactions within Gale. I find that most Mastcam bedrock spectra in this region lack the absorptions associated with hematite found throughout the Murray, and instead show deeper absorptions shifted toward longer wavelengths that are more consistent with Fe-smectites such as nontronite. Elemental chemistry from ChemCam supports this interpretation, as SiO, MgO, Li, and the chemical index of alteration are elevated in this region. Combined with observations of bedrock sedimentology, this suggests that Sutton Island was deposited in a nearshore or low stand environment, and we hypothesize that the clay minerals were produced in this region due to sub-aerial exposure and weathering in a semi-arid climate.</p><p>In Chapter 3, I use the Middle Jurassic Carmel Formation from Utah as a terrestrial analog to understand how the history of rock-water interactions is expressed in the rock record on Mars and how we can interpret this history of deposition and diagenesis using visible/near-infrared/short wave-infrared reflectance spectroscopy at rover scales. The Carmel Formation consists of carbonate- and sulfate-rich heterolithic strata deposited in a range of environments from fluvial, aeolian, and coastal sabkha to shallow marine settings. The alteration mineralogy, variable sedimentology, and diagenetic features present makes this formation a good analog for parts of the Murray formation in Gale crater and rocks from the Jezero crater delta front. In this thesis, we find that changes in lake level and climate manifest themselves in diagenetic features and mineralogy in the Carmel Formation with increased carbonate content in marine strata and increased evaporite/clay mineral content in near-shore/playa deposits. These results generally correspond to correlations with sedimentology and bedrock composition observed in Gale and Jezero craters and allows us to better interpret evidence of complex rock-water interactions on Mars using reflectance spectroscopy.</p><p>Although NASA’s <i>Curiosity</i> rover has found evidence of diagenesis, at a variety of scales, the broader extent of diagenesis in Gale crater is poorly constrained. <i>Curiosity</i> has observed extensive evidence of diagenesis at the unconformity between Mt. Sharp group fluvial/lacustrine mudstones and Siccar Point group (SPg) aeolian sandstones, which is part of the much larger Mound Skirting Unit (MSU) that mantles Mt. Sharp. This diagenetic horizon is visible as a light-toned tan, gray, or blue region in color images from both the ground and orbit. In Chapter 4 of this thesis, I use orbital color images and spectroscopy to look for possible evidence of alteration at the MSU unconformity elsewhere in Gale crater. I find that color variations appear at the MSU unconformity across Mt. Sharp and are co-located with detections of alteration minerals such as hydrated silica and phyllosilicates. This suggests that some of the diagenetic alteration observed by <i>Curiosity </i>below the MSU unconformity was extensive across Mt. Sharp. I hypothesize that this diagenesis was primarily driven by differences in permeability, where the more permeable SPg/MSU sandstones provided a conduit for diagenetic fluids that stagnated within and altered the upper few meters of less permeable clay bearing strata in the Mt. Sharp group below. The extensive diagenesis observed in Gale implies that subsurface fluids were long-lived and widespread in this region on Mars. Gaining a better understanding of what rock properties control and influence diagenetic fluid flow on Mars will help us improve the search for ancient aqueous environments, and possible biosignatures, on Mars.</p><p>The work included herein contributes to our understanding of rock-water interactions on Mars by demonstrating how bedrock properties, such as changes in permeability, can affect the flow of diagenetic fluids. These studies emphasize the importance of reflectance spectroscopy as a useful tool for constraining bedrock mineralogy and how it links to variable depositional and alteration environments. This will help guide current and future missions to search for past habitable environments and biosignatures on Mars.</p>

<p dir="ltr">We present a model describing an impact jetting origin for the formation of chondrules, the mm– scale, igneous components of chondritic meteorites which originated during the first few million years of solar system history. The ubiquity of chondrules in both non-carbonaceous and carbonaceous chondrites suggests their formation persisted throughout the protoplanetary disk, but their formation mechanism is debated and largely unexplored in the outer disk.<b> </b>Using the iSALE2D shock physics code, we generate models of the process of impact jetting during mixed material (dunite and water ice) impacts that mimic accretionary impacts that form giant planet cores. We show that the process of impact jetting provides the conditions necessary to satisfy critical first-order constraints on chondrule characteristics (size, shape, thermal history). We then explore the implications of chondrule formation by impact jetting during the formation of giant planet cores by combining the original results with simulations of giant planet core accretion generated using a Lagrangian Integrator for Planetary Accretion and Dynamics (LIPAD) code.</p><p dir="ltr">The second closest Galilean satellite to Jupiter is Europa, an ocean world with an outer ice shell and subsurface water ocean encapsulating its rocky core. The surface of Europa is covered in double ridges. These features are defined by two topographic highs about 100 meters tall, with a central trough between them, which extend for hundreds of kilometers over the surface of the moon. Accurate models for the formation of features as prominent as double ridges will help to further constrain the interior structure and dynamics of the interior of the body. We use analytical and numerical finite element models to show that the incremental growth of an ice wedge within the ice shell can cause deformation matching the observed size and shape of observed double ridges on Europa. These models indicate that the total height and width of the ridges correspond to the depth of the wedge, so that deeper wedges create shorter and broader ridges. We consider different sources for the wedge material and ultimately argue in favor of local sources of liquid water within the ice shell.</p>

Constraining the behaviour of small fractions of partial melt in a solid silicate matrix has been the focus of numerous experimental petrology studies over several decades, and is an important factor in constraining upper mantle rheology, melt extraction at mid-ocean ridges and mechanisms of core formation in the early solar system. Deformation of partially molten rock has been observed to change melt geometry, and may enhance permeability and interconnectivity of melt otherwise trapped in a solid silicate matrix, although it is uncertain how applicable results of high strain-rate laboratory experiments are to the real Earth. The addition of deformation precludes attainment of textural equilibrium, complicating textural analysis, which has previously relied on extrapolation of 3D textures from quenched and polished 2D sections for hydrostatically annealed samples. X-ray computed tomography gives the potential to visualise sample textures directly in three dimensions, and is becoming popular as a complementary technique for textural analysis in petrologic studies. The aim of this project has been to develop techniques to improve visualisation of small fractions of partial melt within a solid silicate matrix using X-ray CT, to examine textures of various partially molten systems at high PT in hydrostatic, and dynamically deforming systems. Experiments carried out in the FeS-melt, solid olivine system have examined the potential for deformation-enhanced percolation of core forming melts before the onset of silicate melting. Access to the newly designed rotational Paris-Edinburgh Cell (roPEC/rotoPEC) equipment has allowed us to carry out controlled, torsional deformation experiments under PT conditions applicable to planetary interiors. Experiments conducted at lower strain-rates over longer duration than in previously published studies show that deformation enhances connectivity at low melt fractions, at strain-rates down to 10-6s-1. This is in contrast to earlier work suggesting melt textures are unaffected at strain-rates below 10-5s-1. Quenched melt networks have been fully characterised in 3D using multi-scale CT, with voxel sizes down to 70nm for small sample sub-volumes. Results suggest segregation of metallic melt below the silicate solidus could be an efficient process, and should be taken into account in geochemical models of planetary evolution. Experiments on basaltic melt in a solid silicate matrix were conducted in application to upper mantle melting. A heavy element, hafnium, was added to the basaltic glass starting composition to enhance contrast between the basalt and olivine phases during CT scans. In-house micro-CT equipment was used to visualise post-quench run products of hydrostatic and deformation experiments. The doping technique was successful for long-duration, high temperature hydrostatic experiments. Some issues with undissolved / re-precipitated HfO¬2 crystals complicated tomographic imaging of partial melt textures in a number of experiments, particularly those carried out on the rotoPEC equipment, limiting comparison between samples. The doping technique requires further adjustment, but is shown to be a viable way to improve visibility of basaltic melt without significantly affecting melt texture. The X-ray transparent design and fully rotating top and bottom anvils of the rotoPEC allow X-ray tomography to be carried out in-situ while experiments are in progress, enabling collection of 4D datasets. During this project, the rotoPEC equipment was incorporated into two different synchrotron beamlines, to carry out time-resolved studies of textural development within samples of varying composition. The migration of gold melt along fractures with a BN matrix was imaged using 2D radiography, in combination with repeated 3D tomography to fully characterise the 3D fracture geometry. This allowed melt migration velocity to be estimated directly from in-situ observations. These techniques could be developed further to constrain melt migration processes quantitatively for a number of geological systems in the near future.

<p dir="ltr">This dissertation explores the history of water on Mars through the lens of the Mars 2020 Perseverance rover mission at Jezero crater. In particular, I use in-situ rover observations to characterize evidence of past surface alteration at Jezero crater. I also present investigations of a modern lake analog on Earth to contextualize potential past depositional processes within the Jezero paleolake system.</p>

The ultimate goal of this dissertation was to better understand what the Apollo sample collection tells us about the impact history of the Moon. My main research tool is a computer code called Cratered Terrain Evolution Model (CTEM). CTEM is a Monte Carlo landscape evolution code developed to model a planetary surface subjected to impacts. While the main effect of impact cratering that CTEM simulates is elevation changes of the landscape through the excavation process of craters and the deposition of ejecta, I worked to extend the capabilities of the code to study problems in material transport. As impact cratering is a dominant process on the surface of Moon, the stratigraphy of lunar geology is thought to be composed of stacks of impact-generated ejecta layers. Each individual impact generates ejecta that is sourced from varying depths of the subsurface. This ejecta contains a rich abundance of material containing information, including composition and datable impact products, such as impact glasses. The extensions to the CTEM code that I developed allows me to track all ejecta generated during a simulation and model the complex history of the lunar regolith.

Die Kartierung planetarer Körper stellt ein wesentliches Mittel der raumfahrtgestützten Exploration der Himmelskörper dar. Aktuell kommen zur Erstellung der planetaren Karten Geo-Informationssysteme (GIS) zum Einsatz. Ziel dieser Arbeit ist es, eine GIS-orientierte Prozesskette (Planetary Mapping System (PMS)) zu konzipieren, mit dem Schwerpunkt geologische und geomorphologische Karten planetarer Oberflächen einheitlich durchführen zu können und nachhaltig zugänglich zu machen. / Mapping of planetary bodies has been an important asset in the space-based exploration. The aim of this work is to create a mapping chain (Planetary Mapping System (PMS)) with the focus on geological and geomorphological mapping of planetary surfaces, using Geo-Informationsystems (GIS) and an associated data model. Along with a user-targeted design the PMS has been developed in order to provide means for a homogeneous digital mapping workflow and storage of information that allows comparability of map results and the extraction of new information.

Craters formed by impact and volcanic processes are among the most fundamental planetary landforms. This study examines the morphology of diverse craterforms on Io, the Moon, Mars, and Earth using quantitative, outline-based shape analysis and multivariate statistical methods to evaluate the differences between different types of. Ultimately, this should help establish relationships between the form and origin of craterforms. Developed in the field of geometric morphometrics by paleontological and biological sciences communities, these methods were used for the analysis of the shapes of crater outlines. The shapes of terrestrial ash-flow calderas, terrestrial basaltic shield calderas, martian calderas, Ionian paterae, and lunar impact craters were quantified and compared. Specifically, we used circularity, ellipticity, elliptic Fourier analysis (EFA), Zahn and Roskies (Z-R) shape function, and diameter. Quantitative shape descriptors obtained from EFA yield coefficients from decomposition of the Fourier series that separates the vertical and horizontal components among the outline points for each shape. The shape descriptors extracted from Z-R analysis represent the angular deviation of the shapes from a circle. These quantities were subjected to multivariate statistical analysis including principal component analysis (PCA) and discriminant analysis, to examine maximum differences between each a priori established group. Univariate analyses of morphological quantities including diameter, circularity, and ellipticity, as well as multivariate analyses of elliptic Fourier coefficients and Z-R shape function angular quantities show that ash-flow calderas and paterae on Io, as well as basaltic shield calderas and martian calderas, are most similar in shape. Other classes of craters are also shown to be statistically distinct from one another. Multivariate statistical models provide successful classification of different types of craters. Three classification models were built with overall successful classification rates ranging from 90% to 75%, each conveying different shape information. The EFA model including coefficients from the 2nd to 10th harmonic was the most successful supervised model with the highest overall classification rate and most successful predictive group membership assignments for the population of examined craterforms. Multivariate statistical methods and classification models can be effective tools for analyzing landforms on planetary surfaces and geologic morphology. With larger data sets used to enhance supervision of the model, more successful classification by the supervised model could likely reveal clues to the formation and variables involved in the genesis of landforms.

Planetary science is often limited to only surface observations of planets requiring the development of modeling techniques to infer information about the planet’s interior. This work outlines three separate scientific problems that arose from planetary surface observations, the methodology utilized to explain the formation of these observation, and what we learned about the planet’s interior by solving these problems. Chapter 1 discusses why lunar mascon basins (impact basins associated with a central freeair gravity positive) form for only a limited range of basin diameters. Modeling the full formation of South-Pole Aitken (SPA) basin using a sequential two-code (hydrocode and Finite Element Model) shows that due to SPA’s great size (long wavelength) and the high geothermal gradient of the Moon at impact, the basin’s relaxation process was controlled by isostatic adjustment with minimal influence from lithospheric rigidity or membrane stresses. Additionally, the modeling shows that the Moon was hot and weak at impact. Chapter 2 addresses why there is a lack of olivine abundance on Mars around large impact basins, and the formation of the megabreccia that is associated with an orthopyroxene signature in the circum-Isidis Planitia region. Hydrocode modeling of the excavation of the Isidis forming impact shows the impact was more than capable of excavating mantle material and reproducing the observed megabreccia. This coupled with the lack of olivine signature indicates that the Martian upper mantle is orthopyroxene-rich. Chapter 3 covers the investigation into why the nitrogen ice sheet on Pluto, Sputnik Planitia, is the youngest observed terrain and why the surface is divided into irregular polygons about 20– 30 kilometers in diameter. The utilization of a new parameterized convection model enables the computation of the Rayleigh number of the nitrogen ice and shows that the nitrogen ice is vigorously convecting, making Rayleigh–Bénard convection the most likely explanation for these polygons (Trowbridge et al., 2016). Additionally, the diameter of Sputnik Planitia’s polygons and the dimensions of its ‘floating mountains’ of water ice suggest that its nitrogen ice is about five to ten kilometers thick (Trowbridge et al., 2016). The estimated convection velocity of 1.5 centimeters a year indicates a surface age of only around a million years (Trowbridge et al., 2016). The accumulation of this work is three chapters that use three separate techniques to further understand three separate planets.