Theses and Dissertations from UMD
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Item A prototype miniature mass spectrometer for in situ analysis of trace elements on planetary surfaces(2021) Farcy, Benjamin Jacob; Arevalo, Ricardo D; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Interrogation of the chemical composition of rocky planets provides a deeper understanding of the history and evolution of the solar system. While laboratory studies of returned samples and remote sensing surveys of planetary surfaces can give insight into planetary history, one technique that has delivered major insights to planetary geology is in situ measurements of a planetary surface via mass spectrometry. Here, a new approach to spaceflight mass spectrometry is discussed, including an overview of the pursued scientific questions, the analytes targeted, and the prototype hardware in development. This effort constitutes the scientific and technological foundation of a landed planetary mission. This dissertation focuses on the history and evolution of the Earth-Moon system as recorded by trace elements. Specifically, the abundance and distribution of the heat producing elements (HPEs: K, Th, U) and their implications for mantle dynamics is considered. The radiogenic heat produced from K, Th, and U drives mantle convection, volcanism, and planetary dynamos. To understand better the chemical dynamics of radiogenic heat distribution in the Earth, the HPE abundance of a series of oceanic basalts was statistically analyzed. This analysis revealed the K/U ratio of the mantle and how it changes due to the enrichment or depletion of incompatible elements. The HPE abundance of the lunar interior was also discussed as a target of a future investigation, along with a series of trace element proxies meant to probe the lunar farside mantle. Further, an analysis of lunar farside craters provides a series of landing sites for an in situ mission, specifically for their surficial exposure of upper mantle material and later emplacement of lunar basalts. To access the trace element systems discussed in this dissertation, a prototype miniature inductively coupled plasma mass spectrometer (ICPMS) was developed to analyze trace elements in situ for landed planetary missions. First, the capability of the plasma to atomize and ionize input material was investigated. A plasma operating at reduced pressure can achieve 99\% ionization efficiency of most elements on the periodic table, with as much as a 50 to 100 times reduction in gas load and forward power compared to commercial systems for both He and Ar based plasma ion sources. The plasma system was integrated with a quadrupole mass spectrometer via a series of DC ion optics and vacuum housing, with its ion current and peak resolution optimized. Quantative data for an analyte spectrum of Kr demonstrates the ability for this instrument to resolve individual mass peaks, which lead to an accuracy and precision measurement of isotope ratios. This effort represents an end-to-end prototype miniature ICPMS, successfully demonstrating a viable instrument for landed planetary missions.Item DETERMINATION OF SIDEROPHILE ELEMENT CHARACTERISTICS THROUGHOUT LUNAR HISTORY: IMPLICATIONS FOR THE LUNAR MAGMA OCEAN AND LATE HEAVY BOMBARDMENT(2014) Sharp, Miriam; Walker, Richard J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Examining the chemical behavior of highly siderophile elements (HSE) in impact events and during planetary differentiation can illuminate geologic processes that have affected the Moon. This dissertation addresses impactor compositions during the putative late heavy bombardment and the chemical composition of the evolving lunar magma ocean at both the times of core segregation and crust formation. Concentrations of the HSE Re, Os, Ir, Ru, Pt, and Pd and 187Os/188Os isotopic compositions are reported for seven Apollo 17 and four Apollo 16 impact melt rocks. Most Apollo 17 samples examined here as in prior studies are characterized by very similar HSE signatures, consistent with a common impactor that had suprachondritic Ru/Ir, Pd/Ir, and Re/Os. In contrast to the Apollo 17 signature, the Apollo 16 impact melts have a wider range of Ru/Ir, Pd/Ir, and Re/Os. This compositional range might be the result of sampling at least three impactor signatures at this site. Experimentally determined plagioclase-melt partition coefficients are also presented. These partition coefficients are used to estimate the concentrations of Sr, Hf, Ga, W, Mo, Ru, Pd, Au, Ni, and Co in a crystallizing lunar magma ocean at the point of plagioclase flotation. Plagioclase-melt derived concentrations for Sr, Ga, Ru, Pd, Au, Ni, and Co are also consistent with prior estimates. Estimates for Hf, W, and Mo, however, are higher. These elements may have concentrated in the residual liquid during fractional crystallization, due to their incompatibility. Experimentally determined metal-silicate partition coefficients are used to constrain the concentrations of W, Mo, Ru, Pd, Au, Ni, and Co in the lunar magma ocean at the time of core formation. The resulting lunar mantle estimates are generally consistent with previous estimates for the concentration of these elements in the lunar mantle. Together, these new results are used to present a compositional timeline for the Moon between the crystallization of the lunar magma ocean and the late heavy bombardment.