ORCID
http://orcid.org/0000-0002-4737-278X
Date of Award
Summer 8-15-2019
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Our understanding of planetary bodies and their surfaces originates from measurements made by spacecraft instruments and laboratory analysis of extraterrestrial materials. Integration of these datasets can significantly advance the fields of planetary geology and geochemistry. The goal of my dissertation research has been to develop novel methods for interrogating extraterrestrial samples and planetary regoliths, with an emphasis on integrating these complementary datasets. Additionally, my research has focused on utilizing ‘big data’ within the geoscience and planetary science communities, whether that data be geospatial or geochemical in nature. My dissertation research involves two separate, but related projects: (1) coupling Apollo 17 sample analyses with orbital observations from the Lunar Reconnaissance Orbiter Camera (LROC); and (2) development of quantitative compositional mapping (QCM) and lithologic mapping (LM) techniques using the electron microprobe, with specific applications demonstrated using vestan and lunar meteorites. For the Apollo 17 photometry research, the effects of composition, surface maturity, mineralogy, and glass content on the photometric properties of the lunar surface were investigated using Apollo 17 soil compositions as ground truth. A regional Hapke photometric parameter map of Taurus-Littrow Valley (TLV) on the Moon was produced and provides information about the photometric properties of the lunar regolith at a pixel scale of ~5 mpp. Finally, an empirical calibration was developed to relate the photometric properties (e.g., single scattering albedo) of the surface to the mafic content of Apollo 17 soils (wt.% MgO+FeO+TiO2). This relationship was used to generate a regional, topography-corrected compositional map of the TLV at high-resolution (~5 meters per pixel; mpp). Specifically, LROC Narrow Angle Camera (NAC) images were combined with NAC-derived digital terrain models to solve for photometric parameters by taking local illumination geometry into account, and thus allowing photometric parameters to be determined at a pixel scale of NAC DTMs (~5 meters per pixel). Locations of the Apollo samples and Lunar Roving Vehicle (LRV) stations, along with physiochemical information of soils collected from those stations, were used to precisely located each sample in NAC images, and to determine the correlation between the single scattering albedo and various measures of composition such as the alumina (Al2O3) content, which corresponds to high-albedo anorthositic components, or the mafic index (FeO+MgO+TiO2), which corresponds to the low-albedo mafic mineral components. The strongest correlation was observed for the mature soils, presumably because the soil maturation process breaks rocks and minerals down to a similar fine grain size. Additionally, the photometric data are self-consistent for incidence angles less than ~60 degrees. Using Bear Mountain as a test case, we describe a very effective method for removing slope effects, except for the steepest slopes where immature regolith occurs, by using the photometric parameters determined from NAC DTM data to account for local illumination geometry. Finally, we make inferences about the local geology, where for example, we examine the photometric characterization of Tycho impact melt at Apollo 17 and discuss the potential for Tycho impact melt in Station 2 soils. For the project on vestan and lunar meteorites, my dissertation research involved developing data processing protocols, multivariate statistical classification routines, and data interpretation workflows for QCM and LM. These methods, along with standard geochemical analyses (e.g., electron probe microanalysis and instrumental neutron activation analysis), were used to quantitatively characterize the mineralogic and lithologic heterogeneity (modal abundance and mineral compositions) of vestan and lunar meteorite samples using non-destructive techniques. For example, six paired howardites, collected from the Dominion Range, Antarctica, during the 2010 ANSMET field season, were extensively characterized using petrography, electron probe microanalysis (EPMA), laser ablation ICP-MS, instrumental neutron activation analyses (INAA), and fused-bead (FB) analysis by EPMA. These howardites contain abundant lithic clasts of eucritic and diogenitic compositions, as well as atypical lithologies only recently recognized (dacite and Mg-rich harzburgite). Additionally, we identified secondary material (breccia-within-breccia and impact melt) derived from multiple impact events. We describe the characteristics of the howardites, and the lithic clasts they contain, to (1) establish the range and scale of petrologic diversity, (2) recognize inter- and intra-sample mineralogical and lithological heterogeneity, (3) confirm the initial pairing of these stones, and (4) demonstrate the magmatic complexity of Vesta, and by inference, early formed planetesimals. We identified a minimum of 21 individual lithologies represented by lithic clasts >1 mm, based on textural and geochemical analysis; however, more lithologies may be represented as comminuted mineral fragments. Large inter- and intra-sample variations exist between the howardites, with distinct diogenite:eucrite and basaltic eucrite:cumulate eucrite ratios, which may be identifiable in Dawn data. We conclude that these meteorites are fragments of the megaregolith and have the potential to represent the largest sample of the vestan surface and are therefore ideal for remote sensing calibration studies. In summary, the results from my dissertation projects are used to: (1) correlate the photometric properties of the lunar regolith to physiochemical characteristics of Apollo 17 soil samples and address outstanding science questions at the Apollo 17 landing site (e.g., characterization of impact melt from Tycho crater); and (2) assess the extent of magmatic differentiation in the vestan crust, and by inference early planetesimals. This dissertation offers new methods for investigating small-scale compositional variations on the Moon; and provides new, highly effective methods for petrologic investigations of complex samples for which only limited quantities exist (e.g., returned lunar and asteroid samples).
Language
English (en)
Chair and Committee
Bradley L. Jolliff
Committee Members
Raymond E. Arvidson, Robert F. Dymek, Michael J. Krawczynski, Mark S. Robinson,
Recommended Citation
Hahn, Timothy Michael, "Investigation and Classification of Planetary Materials and Surfaces using Novel Methods to Analyze Large Compositional Datasets: Quantitative X-ray Compositional Mapping and Lunar Reconnaissance Orbiter Narrow Angle Camera Photometric Analysis" (2019). Arts & Sciences Electronic Theses and Dissertations. 1907.
https://openscholarship.wustl.edu/art_sci_etds/1907
Comments
Permanent URL: https://doi.org/10.7936/6ds7-me94