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ItemSubsurface Sediment Mobilization on Mars: Insights Provided by Orbital Remote Sensing Datasets(Georgia Institute of Technology, 2021-08-24) Dapremont, Angela M.Mud volcanism, a specific type of subsurface sediment mobilization process known to occur on Earth, has been suggested to explain the formation of morphologically diverse edifices across the surface of Mars. Previous studies have provided valuable knowledge about the morphometry, morphology, and geologic setting of putative Martian mud volcanoes. However, major knowledge gaps pertaining to the compositional characteristics of these features remain. This dissertation primarily focuses on the use of multiple orbital remote sensing datasets to investigate the mineralogical characteristics of putative Martian mud volcanoes. The validity of the mud volcanism hypothesis for pitted cones in a northern hemisphere study region of Mars is assessed, and the mineralogy of postulated Martian mud volcanoes is examined on a global scale through the use of some of the highest resolution orbital datasets currently available to study surface features on Mars. This dissertation also provides supplemental knowledge to these compositional analyses through the incorporation of an expanded morphometric dataset, a spatial analysis methodology, and the first application of an analytical modeling technique to the study of proposed mud volcanoes on Mars. Microbial activity has been documented at both onshore and offshore mud volcanism system sites on Earth. Therefore, the possibility that this geologic process once operated on the surface of Mars is intriguing given the astrobiological potential of the associated locations, as well as the ability to study sediments that would otherwise be inaccessible and possibly represent life in the deep biosphere of a second terrestrial planet in the Solar System. The study of this geologic process on Mars is also worthwhile due to implications for Martian climate, comparative planetology, and future landed mission exploration of the Martian surface.
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ItemModeling and Observations of High-silica Magmatic Systems on Earth and Mars(Georgia Institute of Technology, 2021-07-27) Eggers, Gabriel L.On Earth, evolved felsic crust is commonly associated with plate tectonics, specifically subduction zones, and the role of water in modulating melting conditions and phase equilibria in the mantle and crust. As Mars lacks evidence of both plate tectonics and extensive water, felsic rock is unexpected there. However, new studies via remote sensing and in situ observation indicate a wider range of primary rock compositions on Mars, suggesting an incomplete understanding of how these materials form. Nili Patera, a caldera on the Syrtis Major shield volcano, has been a locus of compositional research on Mars, including the first detection of bedrock spectrally consistent with evolved felsic material. Using visible/near-infrared data from the CRISM instrument aboard the Mars Reconnaissance Orbiter, the extent of this feldspathic terrane in Nili Patera is mapped and its relation to surrounding mafic units is investigated. This provides important controls such as the areal extent (a proxy for volume) and relative age that can be used to constrain its magmatic formation history. A high-silica magma system on Earth, the Laguna del Maule volcanic field in Chile, is also studied. A stochastic magmatic model unifying dynamics and compositional understanding of magma system evolution is used to generate numerous realizations using known Laguna del Maule conditions and exploring a range of unknown magmatic fluxes in the crust. Forward models are developed and used to transform the magmatic model outputs to observable geophysical signals in gravity, magnetotellurics, and seismic velocity, which are evaluated against field measurements to determine a probable history of the Laguna del Maule magmatic system and investigate current arguments about the structure and supports of shallow, silicic systems. Together, these studies elucidate our understanding of how high-silica systems can form and evolve in disparate conditions.
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ItemThe impacts of atmospheric radiation on studies of planetary habitability(Georgia Institute of Technology, 2018-07-26) McDonald, George D.The conditions required for Earth-like life to emerge on a planet are thought to include the presence of liquid water, the availability of energy, the existence of organic material, and shielding from high energy charged particles. There are situations when determining whether these conditions exist on a planetary body is not possible without a detailed understanding of the radiative processes occurring in a planet’s atmosphere. In this work, studies of the radiative flux and transfer within planetary atmospheres are carried out in order to elucidate whether certain planetary bodies may be habitable. The first section of this work quantifies the impinging X-ray flux on sub-Neptune sized planets in the Kepler spacecraft dataset. This study determines the conditions for such planets to be stripped of their primordial atmospheres, with implications for the stability of liquid water on their surfaces. In the second part, the absorption of light in the atmosphere of Saturn’s largest moon Titan is modeled in order to understand how close to the surface one has to be to detect organic molecules of prebiotic relevance, including amino acids and nucleobases.
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ItemThe preservation, distribution, and detectability of lipid biomarkers in the Atacama desert and implications for Mars(Georgia Institute of Technology, 2017-07-13) Wilhelm, Mary BethDesert environments on Earth are colonized by organisms adapted to desiccation. We hypothesized that extreme and prolonged dryness might impart too great a challenge for microbial survival. To test this, we surveyed biomolecular proxies for soil microorganism activity across a steep rainfall gradient from the driest region within the Atacama Desert in Chile that receives just a few millimeters of precipitation per decade to a few millimeters a year. Lipid biomarker proxies for membrane response to environmental stress, degree of amino acid racemization, integrity of stress proteins suggest that organisms in the driest soils in the Atacama are not or very minimally metabolically active. While dry Atacama soils in this region might not be habitable, we found that dryness leads to greater preservation of biomarkers. Lipids from soil horizons in a 2.5 m vertical profile in the Yungay region were extracted and analyzed using GC-MS and LC-MS. Buried clay units were found to contain 40,000 year old-2 My lipids in an excellent state of structural preservation with functional groups and unsaturated bonds in carbon chains. We then took advantage of the above-mentioned characterized Atacama soil samples to assess the organic detection capability of current and future Mars mission flight-instrumentation including Raman laser spectroscopy and evolved gas analysis. Our data implies that Mars surface soils are too dry to support microbial life, but lipid biomarkers generated during a wetter epoch could be well preserved by hyperaridity if protected from other degradative processes.
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ItemGeophysical and remote sensing study of terrestrial planets(Georgia Institute of Technology, 2016-07-12) Ojha, LujendraThe overarching theme of this dissertation is the study of the evolution of terrestrial planets and its effect on surface processes and planetary habitability. In many regards, planetary habitability is an enthralling yet obscure topic because our understanding is limited by our terrestrial experience. The utmost necessity for habitability, based on terrestrial experience and general chemical principles, is water. The dissertation provides key spectroscopic evidence for contemporary liquid water on Mars. Pure water is highly unstable on Mars, so any water on the surface would likely be salty. The spectral data from Mars further provides evidence for hygroscopic salts called perchlorates that may be aiding in the formation of these present day brine streaks on Mars. Similar hygroscopic salts are found elsewhere on Mars; in every instance their presence occurs near known ice deposits, ancient sedimentary rocks or modern day brines. The important role of these hygroscopic salts in the present and past Martian water cycle and on habitability is discussed. Change is an inevitable part of natural processes, and nowhere is it manifested more exuberantly than in planetary landscapes. Planets evolve, and the corroboration of change is evident in surface features. An effort to understand the evolution of terrestrial planets in our own solar system, to better understand the formation and evolution of terrestrial planets elsewhere in the universe, is the second central theme of the dissertation. Specifically, by using the gravity data from the orbiters, a series of predictions about the InSight landing site is made. These predictions will test the validity of various methodologies and help constrain the radiogenic content of the Martian crust. In the long term, the measurements from InSight will help answer the evolutionary course Mars took, and what effect higher heat flow during the early stage of its history may have had on the loss of liquid water from the surface.