Understanding the evolution of planetary climates and corresponding changes to planetary surfaces involves the study of terrains of various ages and morphologies. Here, I study Endeavour and Jezero, two craters within the martian Noachian Highlands. I use multiple approaches \u2014 including sedimentology, stratigraphy, geomorphology, numerical modeling, and the quantitative study of geologic structures in 3D \u2014 and a combination of orbital images from satellites and on-the-ground or in-situ images from rover-based instruments to conduct detailed and ground-truthed studies at both craters. At each site, I characterize the role of water in shaping the surface and thus constrain the climate of ancient Mars. Also presented in this work is a methodological approach to optimize the usage of rover and orbital images for three-dimensional orientation of geologic structures.
\r\n\r\nIn Chapter 2, I find that rockfall is a potential source of erosion on Endeavour\u2019s crater rim. Repeated events of large clasts bouncing downslope and eroding bedrock could have generated incised landforms in the absence of flowing liquid water. Boulder deposits atop other crater-infilling units indicate the process of rockfall continued during or after the Noachian-Hesperian boundary (~2.5-2.7 Ga), potentially continuing to shape the crater rim morphology after regional surface desiccation. In contrast, the Jezero crater strata at Kodiak butte discussed in Chapter 3 are interpreted as either preserved fluvial bars in a braided river or mouth bars in a shallow lake, indicating water was abundant in the crater. Gravel- sized grains were transported by energetic flows, with minimal quiescent settling of fine-grained sediment. Deposits of such settings may have a lower biosignature preservation potential than those of Gilbert deltas, the previous depositional hypothesis. In Chapter 4, I performed traces of beds of the Jezero delta-fan structure in HiRISE and then used apparent dips of a given feature seen from multiple perspectives in rover images to estimate true surface orientations. I confirmed that the orientations of scarps, beds, or other quasi-planar surfaces measured from the highest-available resolution orbital datasets are accurate. However, it is challenging to distinguish hierarchical stratigraphic elements from each other and from erosional surfaces using orbital data, and therefore rover data adds key context for depositional interpretations that inform paleoenviroment. In particular, bedform internal structures could only be determined from rover datasets. In all, through a synthesis of methodological approaches and datasets, I find that the two studied craters potentially record disparate predominant morphology-shaping forces \u2014 dry rockfall in Endeavour, and fluvio-lacustrine activity at Jezero. These sites provide spatial and temporal snapshots of past surface conditions on Mars that can be used to build a more complete narrative of the planet\u2019s history.
", "doi": "10.7907/dry1-3w54", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18617", "collection": "thesis", "collection_id": "18617", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252026-061937325", "primary_object_url": { "basename": "baker_samantha_2026_thesis.pdf", "content": "final", "filesize": 67145016, "license": "other", "mime_type": "application/pdf", "url": "/18617/1/baker_samantha_2026_thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Remote Sensing Aqueous Surface Processes on Planets Red and Blue: From Chemical Weathering Mineralogy on Mars to Water Temperature in Alaska's River Corridors", "author": [ { "family_name": "Baker", "given_name": "Samantha Rose", "orcid": "0009-0001-7705-3261", "clpid": "Baker-Samantha-Rose" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" } ], "thesis_committee": [ { "family_name": "de Kleer", "given_name": "Katherine R.", "orcid": "0000-0002-9068-3428", "clpid": "de-Kleer-K-R" }, { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-C" }, { "family_name": "Fischer", "given_name": "Woodward W.", "orcid": "0000-0002-8836-3054", "clpid": "Fischer-W-W" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Ever since satellites were first launched into space in the 1950s, they have been utilized for critical science on Earth and eventually, around other planets as well. In Chapters 2 and 3, we use hyperspectral imagery and other remotely sensed data to examine the formation of aluminum phyllosilicate on Mars. Al-phyllosilicates across Mars have been proposed to have formed from extensive water leaching of basalt, though regional-specific studies suggest diversity between Al-phyllosilicate-bearing regions. Considering this complexity, in Chapter 2, we reexamine Al-phyllosilicate and its associated minerals in the Nili Fossae region. Using hyperspectral imagery from the CRISM instrument, we used Gaussian fitting to automatically identify and map Al-phyllosilicate and its associated minerals. We find that in contrast to prior interpretations, the Al-phyllosilicate in Nili Fossae most likely formed from weathering of an aluminous volcanic ash rather than from extensive leaching of basalt. In Chapter 3, we expand this analysis to a global survey of 6 Al-phyllosilicate-bearing regions on Mars. We examine the composition and stratigraphy of each region to determine their weathering histories, and we compare the regions to place them in a global context. We find that most of the Al-phyllosilicate on Mars is more consistent with volcanic ash alteration rather than extensive basalt leaching, though some regions are more consistent with basalt leaching. We conclude that the Al-phyllosilicate on Mars did not all form from one process, and our results demonstrate the potential for less extensive alteration and more widespread ash-producing volcanism in Mars\u2019 history than previously thought. In addition to composition, remotely sensed data can also be used to measure temperature. In Chapter 4, we use surface temperature derived from Landsat satellite data to examine the spatial and seasonal patterns of river temperature in Arctic rivers and their surrounding floodplains. Water temperature in the Arctic is interwoven with numerous environmental processes and is responding rapidly to the changing climate, but it is poorly monitored. We demonstrate that the Landsat temperature dataset is accurate for application to Arctic river environments, and we generate and examine water temperature maps of the Yukon River watershed. With these, we show that satellite-based temperature measurements can and should be used to address critical environmental questions in this region.", "doi": "10.7907/vz5n-qn22", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18660", "collection": "thesis", "collection_id": "18660", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282026-024019971", "primary_object_url": { "basename": "thesis_abigail_keebler_2026.pdf", "content": "final", "filesize": 9559989, "license": "other", "mime_type": "application/pdf", "url": "/18660/1/thesis_abigail_keebler_2026.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "From Spectra to Mineralogy: a Remote Sensing Approach to Earth's Arid Dust Source Regions", "author": [ { "family_name": "Keebler", "given_name": "Abigail May", "orcid": "0000-0001-6358-9834", "clpid": "Keebler-Abigail-May" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "de Kleer", "given_name": "Katherine R.", "orcid": "0000-0002-9068-3428", "clpid": "de-Kleer-K-R" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Frankenberg", "given_name": "Christian", "orcid": "0000-0002-0546-5857", "clpid": "Frankenberg-Christian" }, { "family_name": "Thompson", "given_name": "David R.", "orcid": "0000-0003-1100-7550", "clpid": "Thompson-David-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Mineral dust plays a critical role in Earth\u2019s climate and biogeochemical systems, influencing radiative forcing, cloud microphysics, and nutrient fertilization of terrestrial and marine ecosystems. These impacts are strongly dependent on dust mineralogy, particularly the abundance and speciation of iron-bearing phases, clays, and carbonates, which control both the optical properties and chemical reactivity of dust aerosols. Despite this importance, mineralogical properties of dust source regions remain poorly constrained at regional to global scales, limiting the representation of dust processes in Earth system models. Hyperspectral visible to shortwave infrared (VSWIR) remote sensing offers a promising pathway for addressing this gap by enabling spectrally resolved characterization of surface mineralogy globally. However, translating reflectance spectra into quantitative mineral abundances remains challenging due to the nonlinear nature of VSWIR spectra of intimate mineral mixtures. \r\nThis dissertation combines hyperspectral remote sensing, field spectroscopy, and laboratory analyses to improve quantitative interpretation of mineral dust source regions and to evaluate the extent to which mineralogical properties can be retrieved from VSWIR observations. The work is structured around three complementary studies that collectively link global satellite observations, field measurements, and empirical modeling approaches.\r\nFirst, a global analysis of arid dust source regions is conducted using hyperspectral observations from the Earth Surface Mineral Dust Source Investigation (EMIT) mission. A systematic sampling and filtering framework is developed to extract a representative dataset of bare soil reflectance spectra from more than one billion observations. The resulting dataset characterizes global variability in surface albedo and mineralogical absorption features across major dust source regions, revealing distinct regional spectral endmembers associated with differences in mineralogy, including bright iron oxide- and kaolinite-rich Saharan surfaces and darker clay- and carbonate-dominated Asian surfaces. These results demonstrate substantial compositional diversity in dust source regions and provide constraints on surface radiative properties relevant to Earth system modeling.\r\nSecond, we investigate the physical and compositional controls on spectral variability using a novel dataset of co-located in situ VNIR reflectance spectra and laboratory measurements of mineralogy, grain size, and iron speciation. We compare the spectral variability captured in this dataset to that of the EMIT global dust source dataset to evaluate the range of global variability represented. We assess compositional controls on spectral variation, including absorption feature presence, position, and strength, as well as overall reflectance and continuum shape. Clay and carbonate absorption features show systematic but non-linear relationships with mineral presence and abundance, reflecting overlapping absorptions and mixed-phase effects. In contrast, iron oxide abundance exhibits strong, approximately linear relationships with diagnostic absorption features in fine-grained clay-rich sediments. We also identify a distinct population of hematite-bearing sands that display strong absorption features despite low hematite abundance. Radiative transfer modeling shows that grain size and bright mineral matrices significantly modulate iron oxide spectral expression. Overall, these results highlight that composition and sediment physical context in control spectral variability.\r\nThird, the dissertation evaluates empirical approaches for predicting quantitative mineral abundances from VSWIR spectra. Using the coupled spectral-mineralogical dataset, a partial least squares regression model is trained to estimate mineral and iron species abundances. Results show that mineral components which control continuum shape and albedo over the full spectral range, including quartz, feldspar, and iron oxides, can be predicted accurately, while phases that express diagnostic feature in a narrow spectral range, such as clays and carbonates, are less-well predicted. Application of the calibrated models to EMIT reflectance data demonstrates that PLSR models successfully identify the major minerals present in the ground-truth data. Compared with EMIT mineralogy products, the empirical approach provides several advantages. In particular, the models improve quantitative retrievals of carbonate abundance, and more frequently resolve complex multi-mineral assemblages containing combinations of clays, carbonates, and evaporite minerals within individual spectra. The models produce reasonable values when applied to spectra from sediment types outside the training dataset, suggesting promising transferability across heterogeneous dust source environments. Together, these findings demonstrate both the potential and current limitations of empirical inversion approaches for hyperspectral mineral retrieval and highlight their utility as a complement to existing feature-based remote sensing frameworks.\r\nTogether, these results provide a framework for improving quantitative interpretation of hyperspectral observations of Earth\u2019s bare sediment surface. By linking global-scale satellite data with field-based measurements and empirical modeling, this work advances the ability to retrieve physically meaningful mineralogical information from VSWIR remote sensing. These improvements are essential for better constraining the radiative and biogeochemical impacts of mineral dust in Earth system models and for extending hyperspectral approaches to future Earth and planetary remote sensing missions.", "doi": "10.7907/ce3x-6f96", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17382", "collection": "thesis", "collection_id": "17382", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-233903333", "primary_object_url": { "basename": "Seeger_Christina_2025_Thesis.pdf", "content": "final", "filesize": 70932931, "license": "other", "mime_type": "application/pdf", "url": "/17382/1/Seeger_Christina_2025_Thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Surface Evolution on Basaltic Bodies: Tectonic, Geomorphic, and Diagenetic Modification on Io and Mars", "author": [ { "family_name": "Seeger", "given_name": "Christina Hope", "orcid": "0000-0003-4993-9724", "clpid": "Seeger-Christina-Hope" } ], "thesis_advisor": [ { "family_name": "Grotzinger", "given_name": "John P.", "orcid": "0000-0001-9324-1257", "clpid": "Grotzinger-J-P" }, { "family_name": "de Kleer", "given_name": "Katherine R.", "orcid": "0000-0002-9068-3428", "clpid": "de-Kleer-K-R" } ], "thesis_committee": [ { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "orcid": "0000-0001-9324-1257", "clpid": "Grotzinger-J-P" }, { "family_name": "de Kleer", "given_name": "Katherine R.", "orcid": "0000-0002-9068-3428", "clpid": "de-Kleer-K-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "All planets and moons in the Solar System evolve over geologic timescales, though the processes affecting each body vary widely depending on gravity, atmosphere thickness and composition, volcanic activity, and perhaps most importantly, the presence of a hydrologic cycle. This dissertation investigates the surface evolution of two basaltic bodies in our Solar System: one that has barely changed in 3.5 billion years, and one that changes almost daily. Jupiter\u2019s moon Io is continually resurfaced by large-scale volcanic eruptions of low-viscosity lava and sulfur dioxide gas, driven by interior heating generated by diurnal tidal stresses. Such tidal stresses have been linked to eruptive activity and tectonic ridge formation on other moons like Titan and Europa; while they strongly influence Io, they are orders of magnitude weaker than the crustal subsidence stresses which control the expression of tectonic features on the surface (kilometers-tall mountains and caldera-like volcanic features called paterae). Chapter 2 investigates whether tidal stresses may have any influence on the formation of mountains and paterae. Though no global trends have been identified, I suggest that local correlations between patera orientations and the large volcanic center of Loki Patera may provide insight into the magma plumbing pathways of this unique volcano. As soon as tectonic mountains are uplifted on Io, they are subject to gravity- and seismicity-driven erosional processes tearing them down. In Chapter 3, I present the first regional geologic map of a trio of mountains named Cocytus Montes and identify a new geologic unit\u2014a blocky deposit composed of kilometer-scale slab-shaped blocks of crust\u2014that are visible thanks to the favorable resolution and near-terminator lighting conditions of new Junocam imagery. I explore several new erosional mechanisms for Io that could create these blocks, determining regolith creep-modified cliff collapse to be the most likely. The orders of magnitude higher resolution imagery collected by the Mars Science Laboratory Curiosity rover provides a backdrop for much closer analysis of how sediments moved, deposited, lithified, and were subsequently modified by diagenetic fluids on ancient Mars. Chapter 4 takes advantage of hand-sample scale data to categorize a diverse array of diagenetic fabrics (nodules, pits, color variations) that correlate with the stratigraphy in a region defined by a transition from clay-bearing rocks to sulfate-bearing rocks. I present several hypotheses to explain how the Mg sulfate detected in these nodules and pore-filling cements may have precipitated at depth, to complement current evaporite-driven models. These hypotheses could be tested in the coming years of Mars exploration by the rover, and will provide insights into the longevity of a groundwater system after surface water ceased to flow on ancient Mars. Overall, this work explores the well-studied terrestrial processes of surface modification, degradation, and diagenesis under distinctly alien conditions throughout the Solar System.", "doi": "10.7907/4mfp-zx56", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17045", "collection": "thesis", "collection_id": "17045", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03052025-175659528", "primary_object_url": { "basename": "ParraSergio_PhdThesis_Final.pdf", "content": "final", "filesize": 9240598, "license": "other", "mime_type": "application/pdf", "url": "/17045/1/ParraSergio_PhdThesis_Final.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Location, Location, Location: Insights from Spatially-Resolved Observations of Marine Seep Carbonate Ecosystems and Carbonaceous Chondrite Surfaces", "author": [ { "family_name": "Parra", "given_name": "Sergio Alexander", "orcid": "0000-0002-2637-7960", "clpid": "Parra-Sergio-Alexander" } ], "thesis_advisor": [ { "family_name": "Orphan", "given_name": "Victoria J.", "orcid": "0000-0002-5374-6178", "clpid": "Orphan-V-J" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Fischer", "given_name": "Woodward W.", "orcid": "0000-0002-8836-3054", "clpid": "Fischer-W-W" }, { "family_name": "Orphan", "given_name": "Victoria J.", "orcid": "0000-0002-5374-6178", "clpid": "Orphan-V-J" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Meile", "given_name": "Christof", "orcid": "0000-0002-0825-4596", "clpid": "Meile-C" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Spatially heterogeneous, multi-component systems are prevalent topics of study in geobiology and planetary science. However, previous studies of these systems often represent limited measurements that abstract or separate the sample from its localized context, thereby obscuring or precluding insights into the drivers ultimately shaping these systems. This challenge motivates the work presented in this thesis, where we provide an extensive and spatially-resolved examination of two complex, heterogeneous systems in geobiology and planetary science: marine seep carbonates and carbonaceous chondrite surfaces, respectively. In marine seep systems worldwide, seep carbonates are a mineral byproduct of a microbial metabolism (the anaerobic oxidation of methane, or AOM) and can continue hosting metabolically active microbial communities, including methane-oxidizing microbes. However, much of our understanding of these endolithic microbial communities stems from bulk, centimeter-scale evaluations of microbial identity and/or metabolic activity across a limited number of samples. As such, the range of structural and environmental conditions that ultimately shape the degree and extent of microbial activity in seep carbonates, including AOM, remains relatively under-constrained. To address this gap, Chapters 1-3 investigate carbonate-hosted microbial communities at a methane seep site in Santa Monica. In Chapter 1, we explore carbonate \u2018nodules\u2019 from methane seep sediments at and below the sulfate-methane transition zone (SMTZ), analyzing their mineral composition, internal structures, and hosted microbial communities compared to their host sediment communities and porewater chemistry. We also discuss key implications of the connectivity of seep sediments to nodules over geologic timescales and the preservation of microbial \u2018thumbprints\u2019. Chapter 2 describes rare tripartite associations between two groups of anaerobic methanotrophic archaea (ANME-1 and ANME-2) and a bacterial partner within seep carbonate crusts and other substrates at the seafloor, with implications towards understudied diversity in the syntrophic interactions governing AOM beyond seep carbonates. Chapter 3 examines the impact of seep carbonate internal structure on endolithic communities from various carbonate crusts, revealing similarities and differences between surface and interior communities that may reflect the importance of pore networks in maintaining favorable local environments. In Chapter 4, we pivot to an extensive analysis of spectra from carbonaceous chondrite surfaces. Carbonaceous chondrites (CCs) are a group of meteorites that represent the oldest materials in the solar system, whose mineralogy preserves a record of early alteration processes thought to be shared with certain asteroids. However, most studies connecting specific CCs to specific asteroids have relied on spectroscopic measurements of bulk powder CCs, which are spatially unresolved and destroy textures, thereby hindering tying shared spectral features to particular phases, petrologic contexts, and alteration histories. As such, Chapter 4 presents an analysis of CCs measured using microimaging hyperspectral visible-and-shortwave-infrared (VSWIR) spectroscopy, where we capture chondrite surfaces features at high spatial resolution. We also compare CC spectral features with asteroids using the Expanded Bus-DeMeo taxonomy, which provides a systematic framework to examine and identify shared drivers of spectral diversity within this spectral range, including Fe-bearing minerals from both original and terrestrial alteration processes. Together, these studies emphasize the importance of spatially-resolved sampling across disciplines, specifically in geobiology and planetary science, thereby capturing and highlighting the heterogenous nature of key systems in these fields and bettering our understanding of the factors shaping them.", "doi": "10.7907/c0w0-ns76", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:17281", "collection": "thesis", "collection_id": "17281", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282025-033216413", "type": "thesis", "title": "Fresh Eyes for an Old Moon: ALMA and JWST Perspectives of Callisto", "author": [ { "family_name": "Camarca", "given_name": "Maria Noel", "orcid": "0000-0003-3887-4080", "clpid": "Camarca-Maria-Noel" } ], "thesis_advisor": [ { "family_name": "de Kleer", "given_name": "Katherine R.", "orcid": "0000-0002-9068-3428", "clpid": "de-Kleer-K-R" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Hallinan", "given_name": "Gregg W.", "orcid": "0000-0002-7083-4049", "clpid": "Hallinan-G-W" }, { "family_name": "de Kleer", "given_name": "Katherine R.", "orcid": "0000-0002-9068-3428", "clpid": "de-Kleer-K-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "As though its surface were frozen in time, Jupiter's moon Callisto has seemingly done little more than collect and degrade impact features since its formation some ~4.5 billion years ago. One outcome of Callisto\u2019s quiescence is that its geologic map retains only a few units, with large-scale landforms consisting of either enormous multi-ring impact basins or crater-laden plains. Despite this geologic simplicity, our knowledgebase of Callisto\u2019s material surface properties and volatile ice distributions is limited compared to the other icy Galilean moons. Understanding how Callisto localizes its thermal properties and delicate volatile ices is essential to understanding how long-term particle bombardment, solar insolation, and extended impact damage has sculpted its aged surface. While Callisto\u2019s much more active sibling satellites have scrubbed some or all of their surfaces free of the most ancient records, the oldest surface processes in the Galilean system remain visible today on Callisto. And with large telescope facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the James Web Space Telescope, these surface properties are now accessible to Earth-based observers.
\r\n \r\nIn Chapters 2 and 3 of my dissertation, I complete the icy Galilean satellite ALMA catalogue with the full Callisto dataset which includes leading and trailing hemisphere images at ALMA Bands 7, 6, and 3, corresponding to 343, 223, and 97 GHz, respectively. At these frequencies, we sample the subsurface depths of order a few centimeters down to about half a meter. From these data, I demonstrate that Callisto\u2019s\u2019 subsurface thermal emission is much less susceptible to diurnal variation compared to the other icy satellites and that while Callisto\u2019s largest craters are thermally consistent with much smaller ones, the warm surface anomalies tell a story of impact bombardment not recorded in current geologic maps. Moreover, I identify several cold anomalies associated with large impacts, as well as one that might be relevant to Callisto's tenuous and patchy CO\u2082 atmosphere.
\r\n \r\nIn Chapter 4 of my dissertation, I present the results from a JWST NIRSpec 2.85\u20135.35 micron observing campaign that allowed us to inspect many of Callisto's volatile surface materials for the first time since the end of the Galileo mission in the early 2000s. In this work, I identify the Lofn/Heimdall impact region as Callisto's largest source of non-radiolytic CO\u2082. This particular crater suite may represent one of the best locations on Callisto to look for deep subsurface materials brought to the surface by the impact. Additionally, I propose Callisto's well-known radiolytic CO\u2082 trailing hemisphere bullseye is accompanied by a second bullseye in water ice exposure that may share a common origin.
\r\n\r\nLastly, in Chapter 5, I offer a brief synthesis of the icy moon ALMA survey, an endeavor that fulfills scientific promises that pre-date the array itself.
\r\n \r\nAltogether, this dissertation offers the community two of the key Callisto datasets of the 2020s era of research. Now that ESA\u2019s JUICE mission and NASA's Europa Clipper are en-route to the Jovian system, this research offers a timely complement to what is a blossoming era for Callisto and broader icy satellite exploration.
", "doi": "10.7907/y6t5-en36", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:15095", "collection": "thesis", "collection_id": "15095", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302023-185542422", "primary_object_url": { "basename": "Thesis_20230130_finalized_submitted.pdf", "content": "final", "filesize": 79139952, "license": "other", "mime_type": "application/pdf", "url": "/15095/1/Thesis_20230130_finalized_submitted.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Tracer Transport in Three Dimensions: Dispersion of Methane on Mars, Coupled Chemistry and Dynamics on Exoplanets, and Submesoscale Mixing in the Ocean", "author": [ { "family_name": "Luo", "given_name": "Yangcheng", "orcid": "0000-0003-0983-3650", "clpid": "Luo-Yangcheng" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Callies", "given_name": "Joern", "orcid": "0000-0002-6815-1230", "clpid": "Callies-J" } ], "thesis_committee": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Callies", "given_name": "Joern", "orcid": "0000-0002-6815-1230", "clpid": "Callies-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "One-dimensional (1D) modeling from a horizontally averaged perspective can oftentimes greatly simplify problems in atmospheric and oceanic sciences and thus capture leading-order physics. Meanwhile, 1D numerical models have great advantages such as numerical stability and time efficiency, hence they are widely used to gain insights into complex problems. However, oversimplification by 1D models may cause failures in finding solutions, revealing novel phenomena, and discovering scaling laws in the three-dimensional (3D) real world, and those are when 3D thinking proves its value. Also, the rise in computational power has allowed investigations using 3D numerical models. This thesis discusses three examples of how 3D modeling transcends the limitations of 1D modeling and reveals new solutions, phenomena, and scalings in planetary atmospheres and Earth\u2019s ocean.
\r\n\r\nChapter 2 is focused on the dispersion of methane plumes on Mars and how it can reconcile the discrepancy between observations. In the face of ostensibly inconsistent observational results of methane on Mars, we adopt a novel approach\u2014inverse Lagrangian modeling in 3D space\u2014to find the scenarios in which the inconsistency in the observations can be reconciled and locate the methane source. We find that the inconsistency between the results of the near-surface in situ methane measurements and the satellite remote sensing measurements can be reconciled if and only if an active methane emission hot spot is located in the immediate vicinity of the Curiosity rover in northwestern Gale crater, or unknown physical or chemical processes are rapidly removing methane.
\r\n\r\nChapter 3 presents a novel phenomenon that could exist on exoplanets\u2014self-sustained photochemical oscillations, which is only produced by 3D atmospheric models. We use a 3D, fully coupled, chemistry-radiation-dynamics model to simulate the ozone-NOx-HOx photochemistry in the atmosphere of a tidally locked Earth-like exoplanet in the circumstellar habitable zone, and calculate the transmission spectra during transits. We find that under certain conditions, biological nitrogen fixation like the one on the Earth can drive large-magnitude, self-sustained photochemical oscillations in the atmospheres of terrestrial exoplanets. The resulting large temporal variability in ozone abundance on exoplanets, if observed, may suggest a strong surface NOx emission source, which could signal extrasolar life participating in the nitrogen cycle on exoplanets. Fully coupled, three-dimensional atmospheric chemistry-radiation-dynamics models can reveal new phenomena that may not exist in one-dimensional models, and hence they are powerful tools for future planetary atmospheric research.
\r\n\r\nChapter 4 uses a 3D fluid dynamics model to study the vertical exchange in the upper part of Earth\u2019s ocean that potentially has great implications for the marine ecosystem. We develop scaling laws for the exchange rate between the surface ocean and the ocean interior which is critical to the rate of nutrient supply to phytoplankton near the ocean surface. These scaling laws could substitute the crude 1D parameterizations that are currently widely used in ocean models. We find that submesoscale turbulence energized by baroclinic instability in the ocean mixed layer can induce tracer exchange between the surface ocean and the ocean interior. Various environmental physical parameters affect the exchange rate. The exchange is stronger where the ocean mixed layer is thicker, the Richardson number (defined as the ratio of the squared buoyancy frequency to the squared vertical shear of the horizontal flow) of the thermocline is smaller, and the Richardson number of ocean mixed layer is larger. The associated nutrient supply from the ocean interior to the surface ocean is also expected to be stronger under these conditions.
", "doi": "10.7907/91p7-gg59", "publication_date": "2023", "thesis_type": "phd", "thesis_year": "2023" }, { "id": "thesis:14607", "collection": "thesis", "collection_id": "14607", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05252022-013922276", "primary_object_url": { "basename": "Scheller_thesisdocument_March2022_final_edited.pdf", "content": "final", "filesize": 70105539, "license": "other", "mime_type": "application/pdf", "url": "/14607/4/Scheller_thesisdocument_March2022_final_edited.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "A Multi-Disciplinary Approach: How Aqueous Minerals Hold the Key to Understanding the Climate and Habitability of Terrestrial Planets", "author": [ { "family_name": "Scheller", "given_name": "Eva Linghan", "orcid": "0000-0002-9981-5802", "clpid": "Scheller-Eva-Linghan" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "orcid": "0000-0001-9324-1257", "clpid": "Grotzinger-J-P" } ], "thesis_committee": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Eiler", "given_name": "John M.", "orcid": "0000-0001-5768-7593", "clpid": "Eiler-J-M" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "orcid": "0000-0001-9324-1257", "clpid": "Grotzinger-J-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Understanding the interplay between geological processes and the climate within the ancient pasts of terrestrial planets holds the key to deciphering what makes terrestrial planets habitable. The climates of both Mars and Earth were drastically different in their ancient pasts. Liquid water once flowed on Mars ~3-4 Ga, creating fluvial valleys and aqueous minerals, until Mars dried out to the desert planet we know today. During the Pleistocene (~ 2.6 Ma \u2013 11.7 ka) and Neoproterozoic (640-710 Ma), Earth experienced widespread glaciations and even a global glaciated state, respectively. Aqueous minerals, such as clays and carbonates, record the history of their aqueous environments and can be used to track these dramatic changes in climate and environment. In Chapter 2, I use hyperspectral infrared imagery and high resolution images retrieved by the Mars Reconnaissance Orbiter to characterize the lithology of some of the oldest Noachian ~3.8-4.1 Ga crust exposed on Mars. I document eight geological units and features that will be studied with the Perseverance rover and record the presence of pyroxene-bearing igneous crustal materials, aqueous environments that led to widespread clay formation, and basin-forming impact processes that brecciated the crust. Associated younger Noachian-aged magnesium carbonate-bearing geological units will also be studied and sampled with the Perseverance rover. In Chapter 3, I review magnesium carbonate formation on Earth and Mars and find that textures of nodules, crusts, veins, sparry crystals, and thrombolites/stromatolites, their associated host lithologies and related secondary mineralogy can be used to distinguish between formation within weathering, lacustrine, hydrothermal, diagenetic, or microbially influenced aqueous environments, respectively, with rover analyses. Laboratory analysis of stable and radiogenic isotopes of returned samples will allow us to analyze the surface temperature and atmospheric isotopic composition of ancient Mars. In Chapter 4, I characterize the paragenesis of hydrated carbonates. In frigid environments, carbonates form in hydrated species known as monohydrocalcite (MHC) and ikaite that transform to calcite upon heating. Through petrographic analysis of Pleistocene ikaite pseudomorphs and a review of more ancient examples, I define a new carbonate microtexture, guttulatic calcite, which is diagnostic for carbonate dehydration and can be used to document frigid temperature conditions. In Chapter 5, I characterize the stable carbon, oxygen (\u03b4\u00b9\u2078OCARB), and clumped (\u0394\u2084\u2087) isotope systematics of hydrated carbonates. Through heating experiments of modern MHC, I measure and model change in \u03b4\u00b9\u2078OCARB and \u0394\u2084\u2087 signatures facilitated by equilibrium exchange as MHC is dehydrated. Using the determined correction for dehydration overprint allows reconstruction of precursor ikaite formation temperatures and isotopic signatures. The textural and isotopic proxies can now be used for reconstructing temperatures and isotopic signatures within Pleistocene and Neoproterozoic sedimentary deposits. In Chapter 6, I use the Perseverance rover\u2019s SHERLOC instrument\u2019s deep-UV Raman and fluorescence spectroscopy to discover evidence for two potentially habitable ancient aqueous environments that contain aromatic organic compounds. Spectral and textural observations of the olivinecarbonate assemblage within Jezero crater, Mars reveal carbonation of ultramafic protolith. A separate, later brine formed sulfate-perchlorate mixtures in void spaces. Fluorescence signatures consistent with multiple types of aromatic organic compounds occur throughout these samples, preserved in minerals related to both aqueous processes. These organic-mineral associations indicate that aqueous alteration processes led to the preservation and possibly formation of organic compounds on Mars. In Chapter 7, I model the global water budget and hydrogen isotopic composition (D/H) of Mars, using measured constraints from geomorphology, atmospheric escape rates, volcanic degassing processes, crust volatile content, and D/H. In my simulations, I find that chemical weathering sequestered a 0.1-1 km global equivalent layer of water, decreasing the volume of water participating in the hydrological cycle by 40 to 95% over the Noachian (~3.7-4 Ga) period, reaching present-day values by ~3 Ga. Between 30 and 99% of Martian water was sequestered through crustal hydration, demonstrating that irreversible chemical weathering can increase the aridity of terrestrial planets. In summary, this PhD thesis demonstrates that the formation of aqueous minerals is a major control on terrestrial planet climates and that aqueous minerals can be used to track the conditions of their formation environments.
", "doi": "10.7907/8rj3-6k52", "publication_date": "2022", "thesis_type": "phd", "thesis_year": "2022" }, { "id": "thesis:14182", "collection": "thesis", "collection_id": "14182", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05272021-220554457", "primary_object_url": { "basename": "DanielNeamati_SeniorThesis.pdf", "content": "final", "filesize": 7095381, "license": "other", "mime_type": "application/pdf", "url": "/14182/1/DanielNeamati_SeniorThesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "New Method and Analysis of Proximity Trajectory-Only Learned Dynamics for Small Body Gravity Fields", "author": [ { "family_name": "Neamati", "given_name": "Daniel A.", "orcid": "0000-0002-1555-1433", "clpid": "Neamati-Daniel-A" } ], "thesis_advisor": [ { "family_name": "Chung", "given_name": "Soon-Jo", "orcid": "0000-0002-6657-3907", "clpid": "Chung-Soon-Jo" } ], "thesis_committee": [ { "family_name": "Minnich", "given_name": "Austin J.", "orcid": "0000-0002-9671-9540", "clpid": "Minnich-A-J" }, { "family_name": "Chung", "given_name": "Soon-Jo", "orcid": "0000-0002-6657-3907", "clpid": "Chung-Soon-Jo" }, { "family_name": "Hunt", "given_name": "Melany L.", "orcid": "0000-0001-5592-2334", "clpid": "Hunt-M-L" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" } ], "local_group": [ { "literal": "Senior Undergraduate Thesis Prize" }, { "literal": "div_eng" } ], "abstract": "Recent missions to small bodies in the past decade (e.g., Rosetta, Hayabusa 2, and OSIRIS-REx) have reshaped our understanding of small bodies and inspired new, more-capable future missions. Despite the high demand for more missions, large uncertainties in small body properties make missions challenging. Recent work in stochastic optimal control can ensure safety in the face of uncertainty in state, constraints, and dynamics. These stochastic optimal controllers require a model of the underlying dynamics, which is difficult for proximity maneuvers and landing around small bodies. Shape models and finite element-like models are the state-of-the-art for high-fidelity gravity models, but they are computationally expensive and do not readily incorporate onboard data. No gravity model yet exists that can use short-horizon position and acceleration data from recent trajectories onboard in safety-critical autonomous proximity maneuvers and landing. Therefore, we propose a new trajectory-only learning-based method to develop a gravity model. We consider three learning frameworks: Gaussian Process Models, Neural Networks, and Physics-Informed Neural Networks. For each framework, we assess the benefits, computational costs, and limitations of the framework. We found that the Gaussian Process Model generally outperforms the other frameworks in cases of moderate uncertainty. As the uncertainty declines or the data is sufficiently filtered, Neural Networks with spectral normalization provide more accurate gravity models and are computationally cheaper to evaluate. Lastly, we reflect on the methods in this thesis and recommend possible problem reformulations for future research.
", "doi": "10.7907/4csx-4636", "publication_date": "2021", "thesis_type": "senior_major", "thesis_year": "2021" }, { "id": "thesis:13869", "collection": "thesis", "collection_id": "13869", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09072020-172907018", "primary_object_url": { "basename": "HaydenDissertation_SUBMIT.pdf", "content": "final", "filesize": 79966526, "license": "other", "mime_type": "application/pdf", "url": "/13869/2/HaydenDissertation_SUBMIT.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Exhumed Fluvial Deposits: New Paleohydrological Tools Indicate Long-Duration Fluvial Activity on Early Mars", "author": [ { "family_name": "Hayden", "given_name": "Alistair Thompson", "orcid": "0000-0003-3540-7807", "clpid": "Hayden-Alistair-Thompson" } ], "thesis_advisor": [ { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" } ], "thesis_committee": [ { "family_name": "Fischer", "given_name": "Woodward W.", "orcid": "0000-0002-8836-3054", "clpid": "Fischer-W-W" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "orcid": "0000-0001-9324-1257", "clpid": "Grotzinger-J-P" }, { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Fluvial sinuous ridges are common landforms on Mars that have been used for interpreting the history of ancient martian rivers. They are typically interpreted as eroded casts of an ancient river at a snapshot in time. However, some ridges might instead be channel belts that preserve river history, leading to significant differences in interpretation of paleohydrology, including flow direction, duration, and discharge. In this thesis, I used analog sites on Earth and techniques from fluvial sedimentology and fluvial geomorphology to determine that many ridges are exhumed channel belts, and to create and apply new tools for measuring bankfull discharge and duration of river flow from remote-sensing observations of these sedimentary deposits. I found evidence that rivers on ancient Mars were comparable in size to those on Earth today, and that they flowed for at least millions of years.
\r\n\r\nI examined sinuous ridges in three terrestrial sites to better understand ridges on Mars: the Cretaceous Cedar Mountain Formation and Jurassic Morrison Formation of Eastern Utah, and the Miocene Caspe Formation of Northeast Spain. Ridges at all sites are capped with sandy units rich with dune and bar strata atop a mudstone pedestal and they cross each other at different stratigraphic levels, observations that together indicate that ridges are channel belts exhumed from floodplain sediments \u2014 the most common arrangement of fluvial stratigraphy. By compiling measurements of hundreds of terrestrial channel belts and their associated channels, I found that the best methods to reconstruct paleochannel bankfull geometry from such deposits are to use thickness of channel belts (1-4 times paleochannel depth) or radius of curvature of lateral accretion sets (half the channel width). Ridge width and planview wavelength, common proxies for paleochannel width, are significantly more uncertain due to channel amalgamation and ridge erosion by scarp retreat, which I quantified with geometry and a new erosion model. Intermittency factor converts bankfull discharge to average discharge, enabling measurement of duration of river flow. I calculated the intermittency factor for 206 fluvial deposits and USGS streamgages, and found that it ranges between 0.003-0.7 with a median of 0.10, with values depending on the ratio of catchment-averaged erosion rate to average precipitation but independent of timescale, river size, climate, or grainsize.
\r\n\r\nThroughout the work, I applied the methods to sinuous ridges on Mars to demonstrate their applicability. I found that many ridges are likely channel belts, and that the ancient rivers they represent are likely smaller but longer than previously studies have indicated. Altogether, this contribution enables new quantitative analyses of ancient rivers on Earth and Mars, and provides evidence that ancient Martian climate was capable of supporting liquid water at many locations across the surface for at least millions of years.
", "doi": "10.7907/68ft-xm49", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14049", "collection": "thesis", "collection_id": "14049", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01082021-174930437", "primary_object_url": { "basename": "trumbo_samantha_2021.pdf", "content": "final", "filesize": 13491859, "license": "other", "mime_type": "application/pdf", "url": "/14049/1/trumbo_samantha_2021.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Views of an Ocean World: The Signatures of Internal and External Processes on the Surface of Europa", "author": [ { "family_name": "Trumbo", "given_name": "Samantha Kathleen", "orcid": "0000-0002-0767-8901", "clpid": "Trumbo-Samanth-Kathleen" } ], "thesis_advisor": [ { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Beneath a comparatively thin ice shell, Europa harbors a global, salty, liquid-water ocean in contact with a rocky seafloor, making it an exciting target for exploring habitability in the Solar System. The potential habitability of Europa's ocean depends on its composition, which may be reflected in that of Europa's geologically young, fractured surface. However, two intertwined uncertainties are the degree to which the ocean and the surface are in contact, and the degree to which surface materials truly represent oceanic signatures. The latter is complicated by the fact that Europa\u2019s surface is continuously altered by sulfur plasma and particle irradiation due to its location within Jupiter\u2019s magnetosphere. In this thesis, I utilize a variety of multi-spectral, Earth-based observations of Europa to explore the balance and interplay of internal and external processes in shaping its surface.
\r\n\r\nChapters II and III focus on using visible-wavelength spectroscopy from the Hubble Space Telescope (HST) to understand the chemistry of Europa's surface salts. In Chapter II, I present the detection of irradiated sodium chloride (NaCl) and show that its distribution correlates with geologically disrupted chaos terrain, suggesting an ocean source. In Chapter III, I investigate multiple spectral features across Europa's sulfur-bombarded trailing hemisphere. In comparing their geographies with the distributions of large-scale geology, magnetospheric particle bombardment, and surface color, I identify some features as reflective of purely exogenous sulfur radiolysis products and others as indicative of radiolysis products formed from a mixture of endogenous material and magnetospheric sulfur.
\r\n\r\nChapters IV and V further consider the effects of radiolytic processing through the analysis of infrared spectra obtained with Keck NIRSPEC. In Chapter IV, I report a previously unseen spectral feature at 3.78 \u00b5m in disk-integrated spectra of the trailing hemisphere. Using Hapke spectral modeling, I demonstrate that it represents an unidentified radiolytic product of potential relevance to understanding the alteration of endogenic material. Chapter V considers a radiolytic species thought to be independent of endogenic material -- hydrogen peroxide (H\u2082O\u2082), a species relevant to the oxidation state and habitability of the ocean in the case of mutual exchange through the ice shell. Contrary to laboratory expectations, I observe the largest H\u2082O\u2082 absorptions within salty, low-latitude chaos terrain. I hypothesize that this distribution may reflect decreased hydrogen peroxide destruction due to electron scavenging by CO\u2082 within these same regions, which would suggest an internal carbon source.
\r\n\r\nFinally, Chapters VI and VII present preliminary studies of Europa's thermal emission using four images obtained with the Atacama Large Millimeter Array (ALMA) and a global thermophysical model developed to simulate Europa's expected thermal emission. In Chapter VI, I combine a single ALMA image with an observation from the Galileo Photopolarimeter Radiometer (PPR) to show that a thermal anomaly seen by the PPR and associated with two potential plume detections is better explained by a locally high thermal inertia than by geologic heating. Chapter VII considers all four ALMA images. While much of the large-scale thermal structure can be readily attributed to albedo variation, modeling of the images reveals a number of localized anomalies, which may indicate variations in geothermal heat flow, thermal inertia, or millimeter emissivity. In the absence of the additional observations needed to distinguish between such possibilities, I construct hypothetical maps presenting the ranges of possible thermal inertia and emissivity values.
", "doi": "10.7907/d63b-y030", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14167", "collection": "thesis", "collection_id": "14167", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05202021-183729767", "primary_object_url": { "basename": "RobackThesis-final.pdf", "content": "final", "filesize": 6346301, "license": "other", "mime_type": "application/pdf", "url": "/14167/2/RobackThesis-final.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Investigating Sand Transport and Landslides, and Implications for Past and Present Environments on Mars and Earth", "author": [ { "family_name": "Roback", "given_name": "Kevin Patrick", "orcid": "0000-0001-5209-2873", "clpid": "Roback-Kevin-Patrick" } ], "thesis_advisor": [ { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "orcid": "0000-0002-3060-8442", "clpid": "Avouac-J-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Wind-driven movement of sand and landslide activity are among the most important processes driving modern-day change on planetary surfaces. This thesis uses novel techniques and datasets to investigate the forces driving these processes on the surface of Mars, and also considers possible applications of the techniques described to Earth. Chapter 1 introduces past work done to understand these processes, and outstanding questions our work aims to answer. Chapter 2 presents and tests a new technique which aims to improve predictions of sand transport driven by wind on planetary surfaces by correcting coarse-resolution GCM predictions for the short-timescale fluctuations they miss. Chapter 3 presents new multiyear measurements of ripple migration at two dune fields on the surface of Mars, and applies these measurements, in conjunction with the new techniques described in Chapter 2, to investigate the dynamics of the Martian atmosphere, and test the accuracy of predictions made by Martian climate models. In Chapter 4, we study a large-scale natural sand trap in the Meroe Patera dune field on Mars, and estimate its trapped volume of sand in comparison to the volume of \"missing\" sand in a dune-free shadow zone downwind of the crater. The volume of trapped sand is far less than the missing volume, suggesting past escape of sand from the crater, despite a lack of obvious evidence for such escape in the present day. In Chapter 5, we change focus from sand transport to introduce an analysis of controls on the global distribution of Martian landslides. Chapter 6 discusses the limitations of applying the techniques of satellite image and climate model analysis described in Chapters 2-4 to terrestrial settings, as well as the possible utility of Chapter 5\u2019s method on other planets.
", "doi": "10.7907/gykg-wz60", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:13603", "collection": "thesis", "collection_id": "13603", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12112019-142555725", "primary_object_url": { "basename": "PEMartin_Thesis2019_final.pdf", "content": "final", "filesize": 612559339, "license": "other", "mime_type": "application/pdf", "url": "/13603/1/PEMartin_Thesis2019_final.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Detection and Analysis of Martian Low-Temperature Geochemistry", "author": [ { "family_name": "Martin", "given_name": "Peter Eckels", "orcid": "0000-0003-4243-2090", "clpid": "Martin-Peter-Eckels" } ], "thesis_advisor": [ { "family_name": "Farley", "given_name": "Kenneth A.", "clpid": "Farley-K-A" } ], "thesis_committee": [ { "family_name": "Eiler", "given_name": "John M.", "clpid": "Eiler-J-M" }, { "family_name": "Farley", "given_name": "Kenneth A.", "clpid": "Farley-K-A" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The history of Mars is encoded in the geochemistry of ancient sedimentary Martian rocks and secondary phases. Recent landed missions have provided unparalleled datasets with which to investigate this geochemistry. Accordingly, this thesis is concerned primarily with the in-situ analysis of low-temperature Martian geochemical processes by landed missions, and the attendant Earth-based studies which enrich those in-situ investigations. There are five main studies reported here. The first is an analysis of a Mars-analog environment on Earth. Datasets similar to those that will be produced by the upcoming Mars-2020 rover are used to evaluate the ability of the rover to reconstruct a known paleoenvironment, to identify reference datasets that require further development, and to suggest operational modes that most efficiently use the rover\u2019s resources. The second study is an in-situ noble gas analysis using the SAM instrument on the Curiosity rover to investigate a jarosite-containing sample using a two-step heating analysis for K-Ar dating. The jarosite likely formed at 2.12\u00b10.36 Ga while plagioclase in the sample formed at 4.07 \u00b1 0.63 Ga, indicating that liquid water interactions continued in Gale crater well past the end of the Hesperian period. The following chapter details another noble gas analysis, focusing on cosmogenic dating of surface exposure. In contrast to <100 Ma exposure ages observed at the floor of Gale crater, exposure ages exceeding 1 Ga are detected on the flanks of Mount Sharp. These ages indicate Mount Sharp formed during the Hesperian and has been largely unchanged in the intervening 3.1 Ga. The next study is a reevaluation of the data used to identify the presence of perchlorate in Gale crater. These data suggest that perchlorate is indeed present, but that it must be Amazonian in age, suggesting that rare surface wetting events have caused leaching of this soluble ion into the bedrock. The final study reports the development of a technique for measuring the isotopes in perchlorate using Orbitrap mass spectrometry on Earth, allowing investigation of the formation processes that impact the chlorine isotope ratio of this molecule on both Earth and Mars.", "doi": "10.7907/EF7Y-D584", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13642", "collection": "thesis", "collection_id": "13642", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02192020-182835054", "type": "thesis", "title": "Investigating the Evolution of Surface Water on Mars through Spectroscopy of Secondary Minerals", "author": [ { "family_name": "Leask", "given_name": "Ellen Kathleen", "orcid": "0000-0002-3220-4003", "clpid": "Leask-Ellen-Kathleen" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" }, { "family_name": "Fischer", "given_name": "Woodward W.", "clpid": "Fischer-W-W" }, { "family_name": "Frankenberg", "given_name": "Christian", "clpid": "Frankenberg-C" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Despite its current arid climate, Mars\u2019 surface preserves a wide variety of morphologies and minerals that point to a water-rich past. However, the mechanisms and timing of this environmental change are not yet well understood. In this dissertation, we explore a variety of water-related minerals through visible-shortwave infrared (VSWIR) reflectance spectroscopy to better understand the environmental conditions at the time of their formation, and trace the evolution of surface water on Mars over time. We also demonstrate the capabilities of VSWIR spectroscopy at laboratory and field scales in a Mars analogue environment (Samail Ophiolite, Oman)\u2014an emerging technique for use on future landed missions that enables us to differentiate between spectrally-similar minerals and spot rare minerals that help to constrain environmental conditions and better understand the geologic context of samples. On Mars, we use orbital datasets (predominantly CRISM, the Compact Reconnaissance Imaging Spectrometer for Mars) to investigate secondary minerals in the southern highlands of Mars, focusing on perchlorate, chloride, and sulphate minerals. We identify a previously unknown artifact in the CRISM dataset, which mimics perchlorate absorptions; previous orbital perchlorate detections (including those associated with recurring slope lineae) are not robust when data are reprocessed, suggesting that there may not be orbitally-detectable reservoirs of perchlorate on Mars, which would enable liquid brines to exist at the surface today. A detailed investigation of chloride deposits across the southern highlands of Mars points to an episodic surface-runoff water source rather than upwelling groundwater, a process which continued to create chloride deposits into the Amazonian era. Where chloride and sulphate deposits are in close proximity (Terra Sirenum, Mars), they do not appear to be genetically related as they often are on Earth; instead, they point to chemically distinct groundwater vs. surface water reservoirs in Terra Sirenum through the Hesperian and into the Amazonian. Together, these studies indicate that briny and/or acidic volumes of water at the surface capable of creating mineral deposits continued to exist \u2014 at least episodically \u2014 on Mars into the Amazonian, rather than ceasing much earlier in Mars\u2019 history.
", "doi": "10.7907/TWR4-N128", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:11803", "collection": "thesis", "collection_id": "11803", "cite_using_url": "http://resolver.caltech.edu/CaltechTHESIS:09282019-173537468", "type": "thesis", "title": "Tracking Volatile Elements in Protoplanetary Disks and on Planetary Surfaces", "author": [ { "family_name": "Anderson", "given_name": "Dana Eklund", "orcid": "0000-0002-8310-0554", "clpid": "Anderson-Dana-Eklund" } ], "thesis_advisor": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "thesis_committee": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Batygin", "given_name": "Konstantin", "orcid": "0000-0002-7094-7908", "clpid": "Batygin-K" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Knutson", "given_name": "Heather A.", "orcid": "0000-0002-5375-4725", "clpid": "Knutson-H-A" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "The formation of planets begins with collisions of tiny, micron-sized, dust grains. These grains reside in structures known as protoplanetary disks, rotating disks consisting of gas and dust that encircle young protostars as a natural outcome of star formation. Although the processes of planet formation and evolution take place over millions and billions of years, in our limited view we can only see snapshots of the different stages. Many of the formative processes are difficult, if not impossible, to observe directly. However, evidence of these events exists in the chemical composition of the bulk material and surfaces of planets themselves, the gas and solid components of protoplanetary disks, and planetary debris such as asteroids and comets. This thesis utilizes modeling and observations of the carbon and nitrogen content of protoplanetary disks to shed light on key factors that control the formation and chemical composition of planets. In addition, this thesis advances techniques for the elemental analysis of planetary surfaces facilitating the detection of salts on the surface of Mars.
\r\n\r\nChapter 2 estimates the maximum potential destruction of solid, refractory carbon in protoplanetary disks in an effort to explain the lack of carbon found in meteorites and the bulk silicate Earth relative to the interstellar materials that seeded their formation. In a T-Tauri disk assuming uniform turbulence and passive heating from stellar photons destruction of refractory carbon sources via oxidation and UV photolysis is limited to the warm, photochemically-active disk surface layers. Exploration of distinct disk environments, considering non-idealized mass transport or enhanced disk heating due to active stellar mass accretion, is needed to explain the widespread lack of carbon in rocky solar-system bodies.
\r\n\r\nChapters 3 and 4 present spectral observations by the Atacama Large Millimeter/submillimeter Array (ALMA) of mature, 5-11 Myr-old, protoplanetary disks in the Upper Scorpius region that indicate diverging behavior of the key carbon and nitrogen species in the disk gas as disks evolve. Selective depletion of CO from the gas may cause disk gas masses to be underestimated if based on CO measurements alone and further investigation of additional gas tracers is warranted.
\r\n\r\nDepletion of CO from the gas in the outer regions of disks observed by ALMA may be the result of sequestration of carbon into less volatile species such as CO2 and CH3OH. Chapter 5 explores the fate of CO2 and CH3OH ices entering the inner regions of protoplanetary disks. Carbon returns to CO in unshielded transparent regions of the inner disk surface, consistent with infrared observations, but carbon reservoirs in the disk midplane may be distinct depending on the efficiency of mass transport in the disk.
\r\n\r\nChapter 6 examines the abilities of the Laser-Induced Breakdown Spectroscopy (LIBS) instrument ChemCam on the Mars rover Curiosity in regards to the detection of salts. LIBS analysis of a set of prepared sample pellets containing decreasing concentrations of salt identifies elemental emission lines of Cl, C, and S that are sensitive to changes in chloride, carbonate, and sulfate salt concentrations, respectively, and provides detection limits for ChemCam measurements of these salts.
", "doi": "10.7907/GZSA-DK98", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:13810", "collection": "thesis", "collection_id": "13810", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06092020-122543624", "primary_object_url": { "basename": "Stein_Thesis_Final.pdf", "content": "final", "filesize": 106613613, "license": "other", "mime_type": "application/pdf", "url": "/13810/1/Stein_Thesis_Final.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Investigation of Past Habitable Environments through Remote Sensing of Planetary Surfaces", "author": [ { "family_name": "Stein", "given_name": "Nathaniel Thomas", "orcid": "0000-0003-3385-9957", "clpid": "Stein-Nathaniel-Thomas" } ], "thesis_advisor": [ { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" }, { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" }, { "family_name": "Fischer", "given_name": "Woodward W.", "clpid": "Fischer-W-W" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Planetary surfaces record a history of potentially habitable environments throughout the solar system. This dissertation focuses on the characterization of three planetary surfaces to inform their evolution and past habitability: Earth (Chapter 2), Mars (Chapters 3-4), and Ceres (Chapters 5-6). In chapter 1, we introduce major questions driving the work presented in this thesis. In Chapter 2, we use a combination of UAV-based images and in-situ observations to characterize the processes that control the texture and distribution of modern microbial mats in the Turks and Caicos. We find that the surface texture and distribution of the mats is controlled primarily by subtle differences in elevation that drive significant changes in subaerial exposure time. Sedimentation and mechanical weathering from storm events also play a key role in controlling the distribution of mats. In Chapter 3, we apply a PCA-based regression method to stereo Curiosity Mastcam images to measure the structural orientation of the Murray formation. We constrain the dip to be effectively horizontal, which indicates that the Murray formation predates the creation of Aeolis Mons and is consistent with flat strata being deposited on an equipotential surface in a lacustrine setting. In Chapter 4, we summarize the investigation of networks of reticulate ridges on the surface of several rock slabs in the Murray formation using data from the Curiosity rover. We find that the features are preserved mudcracks that were likely deposited during a lowstand in a lake ~3.2-3.6 Ga. The mudcracks are one of few definitive textural markers of drying in the Murray formation and suggest a history of oscillating lake levels that led to intermittent exposure. In Chapter 5, we catalog bright spots on Ceres and propose mechanisms for their formation. We identify hundreds of Na-carbonate-bearing regions on Ceres. We show with a Monte Carlo impact model that these deposits must have been exposed within the last few hundred Ma. In Chapter 6, we investigate the source of shallow subsurface Na-carbonate deposits. We show that the deposits must have been emplaced in the last ~1 Ga and that the solid-state mobilization of water ice and hydrated Na-carbonates could simultaneously explain the formation of domes and large crater rim Na-carbonate exposures. Chapter 7 synthesizes the major results of this thesis and avenues for future exploration.", "doi": "10.7907/cq9c-sg21", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:11344", "collection": "thesis", "collection_id": "11344", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01172019-113222535", "primary_object_url": { "basename": "witkosky_rebecca_thesis_2019.pdf", "content": "final", "filesize": 19923162, "license": "other", "mime_type": "application/pdf", "url": "/11344/38/witkosky_rebecca_thesis_2019.pdf", "version": "v10.0.0" }, "type": "thesis", "title": "Tectonics in Nevada and Southern California: Subsidence of the Ediacaran Johnnie Formation, Cumulative Offset Along the Lavic Lake Fault, and Geomorphic Surface Development Along the Southern San Andreas Fault", "author": [ { "family_name": "Witkosky", "given_name": "Rebecca Amber", "clpid": "Witkosky-Rebecca-Amber" } ], "thesis_advisor": [ { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Wernicke", "given_name": "Brian P.", "orcid": "0000-0002-7659-8358", "clpid": "Wernicke-B-P" } ], "thesis_committee": [ { "family_name": "Wernicke", "given_name": "Brian P.", "orcid": "0000-0002-7659-8358", "clpid": "Wernicke-B-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "While we know the ages and tectonic histories of many critical geologic events in the history of the Earth, there are still questions regarding the timing of key events and structures that have and continue to influence life on this planet. This thesis includes three separate studies in Nevada and southern California: two potential new methods for measuring/organizing geologic time, and also an analysis of the long-term displacement along an active fault in the eastern California shear zone. In Chapter II, we used tectonic subsidence modeling to find that the Shuram carbon isotopic excursion in the Ediacaran Johnnie Formation likely occurred from 585-579 Ma, and that incision of the Rainstorm Member shelf occurred during the 579 Ma Gaskiers glaciation. The pre-Shuram-excursion chemostratigraphic carbon isotope profiles from the Khufai Formation in Oman and the type locality of the Johnnie Formation in Nevada are both generally positive and therefore possibly correlative. In Chapter III, we determined the cumulative tectonic offset along the Lavic Lake fault, an active structure that ruptured with >5 m of coseismic slip in the 1999 Mw 7.1 Hector Mine earthquake. We calculated a net slip of 960 +70/-40 m, based on the slip vector formed by a vertically separated lithologic contact and a horizontally separated older cross fault. The net slip we calculated is significantly less than a previous estimate that was based on an offset magnetic gradient, a disparity that may be explained by considering off-fault deformation, as well as the unknown depth and nature of the source of the magnetic contrast. In Chapter IV, we explored using a new method for the relative dating of Quaternary geomorphic surfaces, which is based on the positive correlation between increased spectral contrast in thermal hyperspectral airborne imagery and surface age. With field data, we found that desert varnish scores, desert pavement scores, and vegetation spacing estimates also correlate positively with surface age, implying that these factors could contribute to the increased spectral contrast in airborne remote sensing spectra. Additionally, the general increase in the band depth of airborne spectra at 9.16 \u03bcm could be due to increasing clay mineral abundance in progressively heavier desert varnish coatings on older surfaces. The positive correlation observed in this study between surface age and spectral contrast in airborne spectra can perhaps be used to develop a method for relative dating of varnished geomorphic surfaces elsewhere. All of the chapters in this thesis are broadly related by the concepts of geologic time and tectonic activity, which are two aspects of modern geology that are intrinsic to the science as a whole.
", "doi": "10.7907/XTZX-X107", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:11711", "collection": "thesis", "collection_id": "11711", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-115333958", "primary_object_url": { "basename": "NThomas_Thesis_revised_submitted_compressed.pdf", "content": "final", "filesize": 9940420, "license": "other", "mime_type": "application/pdf", "url": "/11711/1/NThomas_Thesis_revised_submitted_compressed.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Remotely Sensing Aqueous Alteration on Mars: Innovative Statistical and Analytical Methods for Large Spectral Datasets", "author": [ { "family_name": "Thomas", "given_name": "Nancy Helen", "orcid": "0000-0003-1989-4860", "clpid": "Thomas-Nancy-Helen" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Knutson", "given_name": "Heather A.", "clpid": "Knutson-H-A" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Fischer", "given_name": "Woodward W.", "clpid": "Fischer-W-W" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Liquid water once flowed on Mars and altered the crust. Aqueous minerals and salts record a rich history of aqueous processes and environmental changes. In this dissertation, I developed and applied innovative analytical and statistical methods to large spectral datasets to better characterize aqueous alteration on Mars. The Mars Science Laboratory (MSL) Curiosity rover is investigating the sedimentary sequence at Gale crater recording a potentially global transition from clay-enriched to sulfate-enriched rocks. Volatile elements like H and Cl are important for investigating aqueous processes but are difficult to quantify in the large ChemCam laser-induced breakdown spectroscopy (LIBS) dataset. In the first part of this dissertation, I measured aqueously altered samples with LIBS in the laboratory under Mars-relevant conditions to develop analytical methods for application to ChemCam. The Murray formation, the lowest exposed strata of the sedimentary sequence, contains 2.6 \u00b1 2.1 wt. % H2O. Carriers of H enrichment including clays, opal, Mg-sulfates, Ca-sulfates, hydrous Mn-oxides, akageneite, and jarosite are identified. Variability in the H content of the Murray formation records multiple aqueous alteration events as well as potential increases in salinity in the Gale crater lake. In the fourth chapter, I measured chlorine in Gale crater using multiple MSL instruments. Cl-enrichments correlated with increased Na2O are detected in the bedrock, in nodular textures, and at vein margins, indicating halite. The scattered, isolated occurrences of chlorides are consistent with late groundwater reworking and remobilization. Halite is concentrated in particular members of the Murray formation; the chlorides may have been emplaced as primary deposits in these members, consistent with varying salinity in the past lakewaters. In the second part of this dissertation, I adapted and applied semi-automated statistical methods called factor analysis and target transformation to the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) dataset to systematically search for hematite in stratified, candidate sedimentary outcrops. Few outcrops containing hematite are found and no obvious analogs to terrestrial iron formations are identified. Future studies will search for hematite in other geologic settings as well as other Fe-bearing phases such as Fe-phyllosilicates and Fe-sulfates to better characterize aqueous processes on Mars.", "doi": "10.7907/8JFC-BY64", "publication_date": "2019", "thesis_type": "phd", "thesis_year": "2019" }, { "id": "thesis:10953", "collection": "thesis", "collection_id": "10953", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05282018-115947263", "primary_object_url": { "basename": "Daven-Quinn-thesis-2018.pdf", "content": "final", "filesize": 155896431, "license": "other", "mime_type": "application/pdf", "url": "/10953/9/Daven-Quinn-thesis-2018.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Regional Structural Geology of Earth and Mars", "author": [ { "family_name": "Quinn", "given_name": "Daven Patel", "orcid": "0000-0003-1895-3742", "clpid": "Quinn-Daven-Patel" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "orcid": "0000-0001-9324-1257", "clpid": "Grotzinger-J-P" } ], "thesis_committee": [ { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Eiler", "given_name": "John M.", "orcid": "0000-0001-5768-7593", "clpid": "Eiler-J-M" }, { "family_name": "Asimow", "given_name": "Paul David", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "orcid": "0000-0001-9324-1257", "clpid": "Grotzinger-J-P" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "This thesis explores the geologic context around several key environmental transitions on Earth and Mars which are expressed at continental margins. Regional mapping techniques are applied to build links between methodologies used to explore rock samples and units \u2014 stratigraphy, structural geology, remote sensing, geochemistry, petrology, and geodynamic modeling. Four research projects are presented: Chapter 2 explores the tectonic context of xenoliths beneath the western margin of North America and illuminates the structural history of the lithospheric underpinnings of the California coast. In Chapter 3, we undertake a structural study of the southern Naukluft Mountains, Namibia, and re-interpret its tectonic context and age. Chapter 4 builds a new method for applying statistical errors to remotely measured planar orientations, and Chapter 5 applies this method to mapping the 3D structure of a globally significant stratigraphy on Mars. We find a long history of interaction with water at the margin of Isidis Basin. Together, these projects demonstrate the application of structural techniques to continental margins on Earth and Mars, and the creation of new techniques to support geological analysis from remotely-sensed data, where structural measurements may be poorly resolved.", "doi": "10.7907/9enj-wn23", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:11026", "collection": "thesis", "collection_id": "11026", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06052018-220558731", "primary_object_url": { "basename": "Wong 2018 A Planetary Perspective of Life (PhD Thesis Final).pdf", "content": "final", "filesize": 11915487, "license": "other", "mime_type": "application/pdf", "url": "/11026/15/Wong 2018 A Planetary Perspective of Life (PhD Thesis Final).pdf", "version": "v5.0.0" }, "type": "thesis", "title": "A Planetary Perspective of Life", "author": [ { "family_name": "Wong", "given_name": "Michael L.", "clpid": "Wong-Michael-L" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Knutson", "given_name": "Heather A.", "clpid": "Knutson-H-A" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "clpid": "Blake-G-A" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "3MT Competition (Caltech)" }, { "literal": "div_gps" } ], "abstract": "Join me on my journey to Jupiter, Titan, Pluto, Earth, and Mars as I seek a deeper understanding of life through the lessons that I learn from each world. How should we define life? What does life do? Why does life exist, and how did it begin? And what do the answers to these questions mean for the prospect of life beyond Earth? No, you\u2019re not going to get any spoilers here. Yes, you actually have to read the manuscript. I spent a lot of time weaving this story together, adding supplementary material to each chapter, connecting the dots between the five planetary bodies that I\u2019ve chosen to tell this tale. There\u2019s a lot in here besides just my published work, including two essays on the origin of life (presented in the Interlude) and two scientific works in progress (presented in the Prologue and the Epilogue). I encourage you to follow the wending tale of my graduate school career from start to finish as I build a planetary perspective of life that I now proudly present to you.
", "doi": "10.7907/KVBE-HJ52", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10746", "collection": "thesis", "collection_id": "10746", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03012018-170927159", "primary_object_url": { "basename": "wong_ian_2018.pdf", "content": "final", "filesize": 6677821, "license": "other", "mime_type": "application/pdf", "url": "/10746/1/wong_ian_2018.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Probing the Trojan-Hilda-KBO Connection: An Empirical Test of Dynamical Instability Models of Solar System Evolution", "author": [ { "family_name": "Wong", "given_name": "Ian Yu", "orcid": "0000-0001-9665-8429", "clpid": "Wong-Ian-Yu" } ], "thesis_advisor": [ { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" } ], "thesis_committee": [ { "family_name": "Knutson", "given_name": "Heather A.", "orcid": "0000-0002-5375-4725", "clpid": "Knutson-H-A" }, { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Batygin", "given_name": "Konstantin", "orcid": "0000-0002-7094-7908", "clpid": "Batygin-K" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "In recent decades, the paradigm of solar system formation has undergone radical change. Many current models posit that a significant reorganization of the outer Solar System occurred after the end of planet formation. Specifically, it is hypothesized that Jupiter and Saturn crossed a mutual mean motion resonance, leading to a chaotic expansion of the ice giants' orbits that disrupted the large population of planetesimals situated further out. While the majority of these bodies were ejected from the Solar System, a fraction of them were retained as the present-day Kuiper Belt, while others were scattered inward and captured into resonances with Jupiter to become the Trojans and Hildas. These dynamical instability models invariably predict that the Trojans, Hildas, and Kuiper Belt objects (KBOs) were sourced from the same primordial body of outer solar system planetesimals. Therefore, a comparative exploration of these minor body populations serves as one of the definitive observational tests of our present understanding of solar system evolution. Over the past four-and-a-half years, I have carried out a diverse series of systematic studies aimed at synthesizing a detailed picture of Trojan, Hildas, and KBOs. By combining novel analyses of archival data with new photometric surveys, I have derived the first debiased color distributions of Trojans and KBOs and expanded our knowledge of their respective size distributions. In addition, I have explored the peculiar color bimodality attested in the all three asteroid populations, which indicates the presence of two sub-populations. Utilizing the full body of observations, I have formulated the first self-consistent hypothesis outlining the formation, composition, and dynamical/chemical evolution of the primordial outer solar system planetesimals, with special attention given to explaining the color bimodality, size distribution shapes, and collisional families. My results lay the groundwork for future studies with next-generation instruments and ultimately, the Trojan flyby mission Lucy.
", "doi": "10.7907/Z9B856BX", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10932", "collection": "thesis", "collection_id": "10932", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05242018-144308725", "primary_object_url": { "basename": "Buz_Thesis_Macro_Micro_Mars_final.pdf", "content": "final", "filesize": 11918023, "license": "other", "mime_type": "application/pdf", "url": "/10932/27/Buz_Thesis_Macro_Micro_Mars_final.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Macro Mars to Micro Mars: Mapping Minerals and Magnetization", "author": [ { "family_name": "Buz", "given_name": "Jennifer", "orcid": "0000-0002-0491-2686", "clpid": "Buz-Jennifer" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" } ], "thesis_committee": [ { "family_name": "Lamb", "given_name": "Michael P.", "orcid": "0000-0002-5701-0504", "clpid": "Lamb-M-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" }, { "family_name": "Fischer", "given_name": "Woodward W.", "orcid": "0000-0002-8836-3054", "clpid": "Fischer-W-W" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Combination of remote sensing data with in-situ measurements provides a fuller understanding of Mars phenomena. This dissertation focuses on integrating macroscopic and microscopic scales of measurement with regard to spectroscopy and magnetization. In the first chapter high resolution orbital spectroscopy (~18 m/px) and imagery (~30 cm/px) are used to identify potential sources for some of the sedimentary rocks investigated by the Curiosity rover and expand the accessible stratigraphy. While we find mineralogies in common outside and inside the crater as well as transport mechanisms, we conclude that additional sedimentary sources and/or modification after transport are required to explain chemical differences and that strata point to multiple episodes of a lake in Gale crater. In the third chapter we conducted a laboratory photometric study on candidate calibration target materials for the Mars-2020 rover. We characterized these target materials for proper calibration and monitoring of the Mastcam-Z instrument to enable mineral identification through reflectance spectroscopy. The fourth and fifth chapters focus on the microscopic magnetizations found within Martian meteorite ALH84001. Chapter four reports on paleomagnetic experiments conducted on isolated carbonate crystals which contain magnetite previously reported to be biogenic. We compare paleomagnetic test results which distinguish between biogenic and abiogenic origin hypotheses and find that the magnetization within the carbonates is most consistent with a shock processes. In chapter five we analyzed the distribution of dipoles within slices of ALH84001 and determined that they lie in a girdle distribution which could be interpreted as resulting from a true polar wander event on Mars. Looking at kilometer scale observations outside of Gale enlightened observations made along the rover transverse path. A high resolution laboratory analysis of calibration materials will enable future multispectral mineralogical explorations. Microscopic analyses of magnetization inform ancient surface processes on Mars and hint at large-scale global change. In each of these chapters our results were only made possible or greatly enhanced by the combination of data sources and scales.
", "doi": "10.7907/Z6EH-M526", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10990", "collection": "thesis", "collection_id": "10990", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-155112365", "primary_object_url": { "basename": "Thesis_v4.pdf", "content": "final", "filesize": 11364608, "license": "other", "mime_type": "application/pdf", "url": "/10990/1/Thesis_v4.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Measuring and Modeling the Interplay between Planetary Orbits, Interiors, Surfaces, and Atmospheres", "author": [ { "family_name": "Buhler", "given_name": "Peter Benjamin", "orcid": "0000-0002-5247-7148", "clpid": "Buhler-Peter-Benjamin" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Avouac", "given_name": "Jean-Philippe", "clpid": "Avouac-J-P" }, { "family_name": "Tsai", "given_name": "Victor C.", "clpid": "Tsai-V-C" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Typically, we only have access to observations that directly probe the instantaneous state of a planet. However, these instantaneous properties are often set by the long-term interplay between several aspects of the planet. I thus use quantitative models of the interactions between the orbital, interior, surface, and atmospheric evolution in the case of three planetary bodies (Mars, Pluto, and the extrasolar planet HAT-P-13b) to gain insight into the underlying physical processes that govern the evolution of planets.
\r\n\r\nIn chapter 2, the interplay between the interior structure and orbital evolution of the gas giant exoplanet HAT-P-13b allows measurements of its orbit to reveal its interior structure. I use telescopic observations of HAT-P-13b to measure its orbit and thus determine its core mass.
\r\n\r\nIn chapter 3, cell-shaped landforms on Sputnik Planitia, the surface of a vast deposit of nitrogen ice covering 5% of Pluto\u2019s surface, are the surface expression of convection within the nitrogen ice that is driven by heat flow from Pluto\u2019s interior. The cells have sublimation pits on them, with smaller pits near their centers and larger pits near their edges. Using a simple model, I calculate the sublimation rate of these pits, which allows the determination of a size-age relationship. I then use the spatial size distribution of pits on cells to calculate their convection rate, which constrains the plutonian heat flow and thus the interior properties of Pluto.
\r\n\r\nIn chapter 4, the interplay of condensation and sublimation between the surface and atmosphere of Mars create a baffling array of uniquely martian morphologies carved into the martian residual south polar CO2 cap (RSPC). Using a multi-year baseline of high-resolution observations to track the evolution of these morphologies, I build a self-consistent conceptual framework capable of explaining the basic mechanisms that give rise to the diversity of landforms that make up the RSPC.
\r\n\r\nIn chapter 5, the secular evolution of Mars' orbit drives the evolution of the equilibrium relationship between the martian atmospheric pressure and the large CO2 ice deposit on the martian south polar cap. I construct the first self-consistent conceptual framework capable of predicting the existence and form of the martian residual south polar cap and the buried CO2 deposit. I then use this framework to compute the secular pressure history of Mars.
\r\n\r\nTogether, the results of these investigations provide new perspective into the fundamental processes driving the formation and evolution of planetary bodies.
\r\n", "doi": "10.7907/MEXZ-2586", "publication_date": "2018", "thesis_type": "phd", "thesis_year": "2018" }, { "id": "thesis:10098", "collection": "thesis", "collection_id": "10098", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03182017-212454688", "primary_object_url": { "basename": "orourke_joseph_2017_thesis.pdf", "content": "final", "filesize": 9981691, "license": "other", "mime_type": "application/pdf", "url": "/10098/1/orourke_joseph_2017_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Divergent Evolution of Earth and Venus", "author": [ { "family_name": "O'Rourke", "given_name": "Joseph Ghilarducci", "orcid": "0000-0002-1180-996X", "clpid": "O'Rourke-Joseph-Ghilarducci" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Knutson", "given_name": "Heather A.", "orcid": "0000-0002-5375-4725", "clpid": "Knutson-H-A" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Jackson", "given_name": "Jennifer M.", "orcid": "0000-0002-8256-6336", "clpid": "Jackson-J-M" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Venus and Earth are similar in terms of size and bulk composition, yet their surface conditions are radically different. Earth has hosted plate tectonics and a global magnetic field for billions of years, sustaining water oceans and allowing life to flourish. A thick atmosphere chiefly composed of carbon dioxide, in contrast, drives a greenhouse effect on Venus that would instantly reduce any terrestrial organism to ash. In this thesis, I present several contributions to the debate raging over whether Venus and Earth resembled each other in the past or if unique circumstances placed these celestial siblings on divergent paths from the start. First, I introduce a new process\u2014precipitation of magnesium-rich minerals\u2014that explains the apparent longevity of Earth's dynamo given plausible assumptions about how the core and mantle lose heat. This mechanism relies on high-temperature equilibration in the aftermath of giant impacts, meaning that Earth's violent birth enabled its clement present. The lack of a magnetic field thus indicates that Venus escaped savage bombardment or simply that sluggish mantle convection insulates the core. My analyses of the size and spatial distributions of impact craters suggest that volcanism proceeds planet-wide at gradual rates rather than as catastrophic resurfacing events, which supports a uniformitarian view of Venus. Modeling of enigmatic features called coronae on Venus also sheds light on the properties of the crust and lithosphere that yield a stagnant lid rather than plate tectonics. Finally, I present a thermal history for Venus that is consistent with these and other available constraints. Various uncertainties in my models highlight the pressing need to gather more data relevant to Earth's deep interior and from the most Earth-like planet in our solar system.
", "doi": "10.7907/Z9JH3J6S", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:10136", "collection": "thesis", "collection_id": "10136", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04132017-163326100", "type": "thesis", "title": "Insights into the Geologic History of Mars\u2019 Northern Lowlands from Near-Infrared Spectroscopy \r ", "author": [ { "family_name": "Pan", "given_name": "Lu", "orcid": "0000-0002-8151-2125", "clpid": "Pan-Lu" } ], "thesis_advisor": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Hydrated minerals, identified on Mars using near-infrared spectroscopy data, reveal new insights into the aqueous processes and evolution of climate in the history of Mars. Through investigations of the mineralogical record using near-infrared spectroscopy, this dissertation focuses on the geologic history and aqueous processes in the northern lowlands of Mars in order to assess the existence of a long-lived global ocean, the extent and volume of Noachian-Hesperian volcanic flows filling the northern lowlands, the nature of aqueous activity in the most recent Amazonian age, and the spectral variability of carbonates. The first chapter reports widespread and diverse mafic and hydrated mineralogy of units associated with impact craters across the northern lowlands. In the lowlands-wide survey, no pervasive carbonate or evaporative salts are found in support of a northern ocean, but we identify widespread phyllosilicates inferred to be Noachian basement materials excavated beneath 1-2 km of mafic lava flows. In the second and third chapters, combined analysis of imagery and spectral data is used to investigate local geologic processes related to liquid water in the knobby terrains of Acidalia and in the vicinity of Lyot crater. Phyllosilicates and hydrated silica are detected in the knobby terrains of Acidalia indicative of a declining prevalence of aqueous alteration through time. We also find diverse mineralogy in the vicinity of Lyot, probably formed in a hydrothermal system and later excavated by the Lyot impact. In contrast, we did not identify mineralization related to local channels that are syn- or post-impact. The fourth study analyzes the spectral properties of unshocked and impact-shocked carbonate rocks on Earth and found similar spectral characteristics between Mars carbonate detections and terrestrial carbonates in impact environments. Using near-infrared spectroscopy, we have identified and characterized the mineralogic record of Mars, and found past environments within the northern lowlands of Mars with varying style and intensity of aqueous alteration through time, with implications for the evolution of Mars climate.
", "doi": "10.7907/Z94747WX", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:10173", "collection": "thesis", "collection_id": "10173", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05152017-105730412", "type": "thesis", "title": "Sedimentary Processes on Earth and Mars: Canyon Erosion, Sand-Ripple Formation, and Mineral Composition", "author": [ { "family_name": "Lap\u00f4tre", "given_name": "Mathieu Gaetan Andre", "orcid": "0000-0001-9941-1552", "clpid": "Lap\u00f4tre-Mathieu-Gaetan-Andre" } ], "thesis_advisor": [ { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" } ], "thesis_committee": [ { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" }, { "family_name": "Farley", "given_name": "Kenneth A.", "clpid": "Farley-K-A" }, { "family_name": "Golombek", "given_name": "Matthew P.", "clpid": "Golombek-M-P" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Over the past few decades, orbiters, landers, and rovers have significantly expanded our understanding of Mars\u2019 hydrology and climate; however, significant knowledge gaps stand in the way of our quest for martian life. In particular, the global drying of the planet remains one of the grandest unsolved mysteries in planetary science. To help unravel this puzzle, we develop new quantitative theories for sedimentary processes with implications for both Earth and Mars. This thesis revolves around three main sedimentary processes \u2013 erosion, deposition, and sediment transport. First, we focus on the erosion of bedrock canyons by water on Earth and Mars. After showing that groundwater seepage erosion is only efficient at carving canyons in restricted conditions, we develop a new hydraulic theory for flow focusing upstream of horseshoe-shaped waterfalls and combine it with waterfall-erosion mechanics to constrain the discharge, duration, and volume of canyon-carving floods on Earth and Mars. We show that martian Hesperian floods were large but short-lived. Second, we investigate fluid and sediment controls on the equilibrium size of bedforms. We develop a comprehensive scaling relation to predict the size of ripples forming in various sedimentary environments, including martian brines and methane flows on Titan, and show that the scaling relation predicts the size of large wind ripples forming under a thin martian atmosphere. This new theory, combined with observations of large-ripple cross-strata in wind-blown sandstones of the Burns formation at Victoria crater, suggests that Mars had a thin atmosphere around the Noachian-Hesperian boundary. Finally, we use orbiter-based inferences of the mineralogy of sands of the Bagnold dunes of Gale crater to disentangle the magnitude of wind sorting and local sediment sources. We develop a new probabilistic framework to invert for surface mineralogy, groundtruth our predictions with compositional datasets provided by the Curiosity rover, and discuss the implications of our findings for mineral sorting by martian winds and paleoenvironmental interpretations of martian wind-blown sandstones. Collectively, these results provide new mechanistic and quantitative constraints on the past hydrology and climate of Mars that are key to assess Mars\u2019 astrobiological potential through space and time.", "doi": "10.7907/Z9RF5S2T", "publication_date": "2017", "thesis_type": "phd", "thesis_year": "2017" }, { "id": "thesis:9838", "collection": "thesis", "collection_id": "9838", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06032016-155530034", "primary_object_url": { "basename": "Siebach_Kirsten_Thesis_2016.pdf", "content": "final", "filesize": 5980738, "license": "other", "mime_type": "application/pdf", "url": "/9838/13/Siebach_Kirsten_Thesis_2016.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Formation and Diagenesis of Sedimentary Rocks in Gale Crater, Mars", "author": [ { "family_name": "Siebach", "given_name": "Kirsten Leigh", "orcid": "0000-0002-6628-6297", "clpid": "Siebach-Kirsten-Leigh" } ], "thesis_advisor": [ { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" } ], "thesis_committee": [ { "family_name": "Asimow", "given_name": "Paul David", "clpid": "Asimow-P-D" }, { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Farley", "given_name": "Kenneth A.", "clpid": "Farley-K-A" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The history of surface processes on Mars is recorded in the sedimentary rock record. Sedimentary rock layers exposed in Gale Crater on the modern crater floor (Aeolus Palus) and on Mount Sharp (Aeolus Mons), which hosts one of the more complete records of transitions between major mineralogical eras on Mars, have been investigated by the Mars Science Laboratory Curiosity rover since landing in August 2012. This dissertation focuses on the formation and diagenesis of the sedimentary rocks in Gale crater in order to assess the compositional diversity of the volcanic sources around Gale crater, the effects of transport processes on the sediment grains, and the volumes and geochemistry of water that transported and cemented the sediments. The first study uses orbital mapping of a distinctive cemented boxwork layer on Mount Sharp to constrain a minimum volume of groundwater available to form this layer, 1 km above the modern floor of Gale, with implications for the formation of Mount Sharp. The other three studies use Curiosity rover imagery and geochemical data to investigate sedimentary rocks in Aeolus Palus and at the base of Mount Sharp. The second study identifies and describes diagenetic synaeresis cracks in the Sheepbed mudstone, at the lowest elevation in Aeolus Palus, with implications for the duration of water saturation of these lake sediments. The third and fourth studies identify and explain geochemical trends in the fluvio-deltaic Bradbury group, the Murray mudstone formation, and the eolian Stimson sandstone, focusing on geochemical diversity in the source regions for each of these units and how different depositional processes are reflected in the geochemical data. The sedimentary system in Gale crater has changed our understanding of Mars by expanding the known variety of igneous rocks, increasing estimates of the longevity of surface water lakes, and showing that there were once habitable environments on our neighboring planet.", "doi": "10.7907/Z97D2S4K", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:8713", "collection": "thesis", "collection_id": "8713", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10272014-105243856", "primary_object_url": { "basename": "Limaye_Ajay_2014_thesis_optimized.pdf", "content": "final", "filesize": 14222230, "license": "other", "mime_type": "application/pdf", "url": "/8713/7/Limaye_Ajay_2014_thesis_optimized.pdf", "version": "v8.0.0" }, "type": "thesis", "title": "Valley Evolution by Meandering Rivers", "author": [ { "family_name": "Limaye", "given_name": "Ajay Brian Sanjay", "clpid": "Limaye-Ajay-Brian-Sanjay" } ], "thesis_advisor": [ { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Thompson", "given_name": "Andrew F.", "clpid": "Thompson-A-F" }, { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Fluvial systems form landscapes and sedimentary deposits with a rich hierarchy of structures that extend from grain- to valley scale. Large-scale pattern formation in fluvial systems is commonly attributed to forcing by external factors, including climate change, tectonic uplift, and sea-level change. Yet over geologic timescales, rivers may also develop large-scale erosional and depositional patterns that do not bear on environmental history. This dissertation uses a combination of numerical modeling and topographic analysis to identify and quantify patterns in river valleys that form as a consequence of river meandering alone, under constant external forcing. Chapter 2 identifies a numerical artifact in existing, grid-based models that represent the co-evolution of river channel migration and bank strength over geologic timescales. A new, vector-based technique for bank-material tracking is shown to improve predictions for the evolution of meander belts, floodplains, sedimentary deposits formed by aggrading channels, and bedrock river valleys, particularly when spatial contrasts in bank strength are strong. Chapters 3 and 4 apply this numerical technique to establishing valley topography formed by a vertically incising, meandering river subject to constant external forcing\u2014which should serve as the null hypothesis for valley evolution. In Chapter 3, this scenario is shown to explain a variety of common bedrock river valley types and smaller-scale features within them\u2014including entrenched channels, long-wavelength, arcuate scars in valley walls, and bedrock-cored river terraces. Chapter 4 describes the age and geometric statistics of river terraces formed by meandering with constant external forcing, and compares them to terraces in natural river valleys. The frequency of intrinsic terrace formation by meandering is shown to reflect a characteristic relief-generation timescale, and terrace length is identified as a key criterion for distinguishing these terraces from terraces formed by externally forced pulses of vertical incision. In a separate study, Chapter 5 utilizes image and topographic data from the Mars Reconnaissance Orbiter to quantitatively identify spatial structures in the polar layered deposits of Mars, and identifies sequences of beds, consistently 1-2 meters thick, that have accumulated hundreds of kilometers apart in the north polar layered deposits.", "doi": "10.7907/Z9MG7MFJ", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:8735", "collection": "thesis", "collection_id": "8735", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12042014-212249920", "primary_object_url": { "basename": "stack_thesis_final.pdf", "content": "final", "filesize": 55316234, "license": "other", "mime_type": "application/pdf", "url": "/8735/1/stack_thesis_final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Reconstructing Past Depositional and Diagenetic Processes through Quantitative Stratigraphic Analysis of the Martian Sedimentary Rock Record", "author": [ { "family_name": "Stack", "given_name": "Kathryn Marie Morgan", "orcid": "0000-0003-3444-6695", "clpid": "Stack-Kathryn-Marie-Morgan" } ], "thesis_advisor": [ { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" } ], "thesis_committee": [ { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Lamb", "given_name": "Michael P.", "clpid": "Lamb-M-P" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Grotzinger", "given_name": "John P.", "clpid": "Grotzinger-J-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "High-resolution orbital and in situ observations acquired of the Martian surface during the past two decades provide the opportunity to study the rock record of Mars at an unprecedented level of detail. This dissertation consists of four studies whose common goal is to establish new standards for the quantitative analysis of visible and near-infrared data from the surface of Mars. Through the compilation of global image inventories, application of stratigraphic and sedimentologic statistical methods, and use of laboratory analogs, this dissertation provides insight into the history of past depositional and diagenetic processes on Mars. The first study presents a global inventory of stratified deposits observed in images from the High Resolution Image Science Experiment (HiRISE) camera on-board the Mars Reconnaissance Orbiter. This work uses the widespread coverage of high-resolution orbital images to make global-scale observations about the processes controlling sediment transport and deposition on Mars. The next chapter presents a study of bed thickness distributions in Martian sedimentary deposits, showing how statistical methods can be used to establish quantitative criteria for evaluating the depositional history of stratified deposits observed in orbital images. The third study tests the ability of spectral mixing models to obtain quantitative mineral abundances from near-infrared reflectance spectra of clay and sulfate mixtures in the laboratory for application to the analysis of orbital spectra of sedimentary deposits on Mars. The final study employs a statistical analysis of the size, shape, and distribution of nodules observed by the Mars Science Laboratory Curiosity rover team in the Sheepbed mudstone at Yellowknife Bay in Gale crater. This analysis is used to evaluate hypotheses for nodule formation and to gain insight into the diagenetic history of an ancient habitable environment on Mars.
", "doi": "10.7907/Z9FN144M ", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:7343", "collection": "thesis", "collection_id": "7343", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12192012-121428518", "primary_object_url": { "basename": "chemtob_thesis_121812_final.pdf", "content": "final", "filesize": 21594275, "license": "other", "mime_type": "application/pdf", "url": "/7343/1/chemtob_thesis_121812_final.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Origin and Evolution of Amorphous Silica Coatings on Young Hawaiian Basalts", "author": [ { "family_name": "Chemtob", "given_name": "Steven Michael", "clpid": "Chemtob-Steven-Michael" } ], "thesis_advisor": [ { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" } ], "thesis_committee": [ { "family_name": "Eiler", "given_name": "John M.", "clpid": "Eiler-J-M" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Ehlmann", "given_name": "Bethany L.", "clpid": "Ehlmann-B-L" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Young basaltic lavas on the Big Island of Hawaii frequently feature brightly colored surface coatings. These coatings, the product of interaction of volcanically-derived acidic fluids with basaltic substrates, provide an opportunity to study the rates and mechanisms of early onset chemical weathering in a natural setting. Lava flows of various ages, from hours to ~40 years, at sites along Kilauea's southwest and east rift zones and at Mauna Loa were visited and sampled to determine the nature and extent of this alteration phenomenon. The coatings are composed of a layer of amorphous silica, 1-80 \u03bcm thick, capped in some cases by a 1 \u03bcm layer of Fe-Ti oxide. Raman, infrared, and
The silicon isotope compositions of silica coatings and basalts were measured to determine the degree of Si mobility during coating formation. Coatings are enriched in
The morphologic, spectroscopic and geochemical observations presented here are most consistent with a dissolution-reprecipitation mechanism for silica coating formation. Acidic solutions dissolved near-surface basalt, then precipitated
We investigated the dynamical paleoclimatology of Mars with a focus on three areas: large scale dynamics, atmospheric collapse, and controls on precipitation and aridity of a warm, wet Mars. We explored the changes, and lack of changes, in the large scale circulation over a range of atmospheric masses. We present the results here, with an emphasis on the response of the winds and the meridional transport.
\r\n\r\nThe conditions for continuous condensation of the CO2 atmospheres in the polar regions, often called 'atmospheric collapse', were explored by simulating the Martian atmosphere over a wide range of obliquities for a wide range of atmospheric thicknesses. As expected, atmospheric collapse occurs at low obliquities, but surprisingly, collapse occurs for high obliquities (up to 40\u25e6) for moderate atmospheric thicknesses (100's of millibars up to 1000 millibars). Using the MarsWRF model, we show that a competition between atmospheric heating feedbacks, including the greenhouse feedback and the heat transport feedback, and the condensation temperature feedback determines whether atmosphere collapse occurs.
\r\n\r\nFinally, we explored the precipitation and aridity of a warm, wet Mars with an active hydrological system. Even an extremely wet climate with a northern hemisphere ocean produces an extremely dry, desert climate in the southern hemisphere, with an equatorial band of rain and run off. Cross-equatorial flows deliver moist air from the northern ocean into the southern region, but topography and the distribution of land versus ocean limit the extent of the rainfall.
", "doi": "10.7907/3D9Y-DC44", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" } ]