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<p>Space weathering refers to the gradual spectral, microstructural, and chemical alteration of airless planetary regoliths due to their exposure to the harsh environment of outer space. Solar wind irradiation and micrometeoroid impacts are the primary space weathering processes at work in our solar system. Although the microstructural and compositional effects of space weathering are small, occurring at the sub-micron scale in individual regolith grains, their collective impact on the spectral signature of planetary surfaces is critical. Space weathering is known to change the slope, albedo, and strength of absorption band features of reflectance spectra acquired by ground- and spacecraft-based instrumentation. In this way, space weathering impedes our ability to determine planetary surface compositions from remote sensing data and pair meteorites with their parent bodies. Thanks to decades of research since the Apollo sample return missions, the planetary science community has developed a comprehensive understanding of how space weathering alters the Moon and silicate-rich asteroids. However, the effects of space weathering on primitive, carbon-rich asteroids—which dominate the outer main belt—are more poorly constrained and very complex. This dissertation aims to improve our understanding of how solar wind irradiation and micrometeoroid bombardment modifies the spectral, microstructural, and chemical properties of carbonaceous asteroidal regoliths. To accomplish this goal, this research experimentally simulates constituent space weathering processes in the laboratory on carbon-rich analog materials. A multi-faceted analytical approach including a variety of electron microscopy and spectroscopic techniques is used to probe the spectral, microstructural, and chemical changes induced by experimental space weathering.</p><p>Chapter 1 of this dissertation provides an introduction to space weathering, including a description of the current state of knowledge in the field as well as the motivation for this research. Similarly, chapter 2 provides an overview of the various experimental simulations and coordinated analytical techniques employed in this work. Chapter 3 initiates the discussion of research accomplished during this doctoral program, presenting a detailed characterization of the spectral, microstructural, and chemical effects derived from simulated solar wind irradiation of a carbonaceous asteroid analog material. More specifically, in chapter 1, I perform high flux (~1013 ions/cm2/s), high fluence (1018 ions/cm2) 1 keV H+ and 4 keV He+ irradiation experiments on the Murchison meteorite. Chapter 2 investigates the role of incident ion flux in solar wind space weathering of carbonaceous asteroidal regolith by performing a set of low flux (~1011 ions/cm2/s) and high flux (~1013 ions/cm2/s) H+ and He+ irradiation experiments on Murchison samples. These experiments are the lowest flux solar wind simulations carried out, to date. Finally, chapter 5 presents results from the first <i>combined</i> ion irradiation and heating experiments performed on a carbon-rich analog using in situ transmission electron microscopy (TEM). In situ TEM is a relatively novel technique in the planetary and geological sciences which allows users to observe the physiochemical changes caused by an external stimuli in <i>real time</i>. The experimental approach used in chapter 5 simulates both solar wind irradiation and micrometeoroid impacts, and, thus, probes the cumulative microstructural and compositional modifications induced by these concurrent space weathering processes. In chapters 3 through 5, I compare my results to previous space weathering simulations and observations of lunar and asteroidal returned samples. Findings from this dissertation advance the existing model of space weathering on carbon-rich asteroids, help inform remote sensing observations from the Hayabusa2 and OSIRIS-REx missions which have rendezvoused with C-complex asteroids Bennu and Ryugu, respectively, and provide experimental ground-truth for analyzing returned samples from these missions.</p>

<p>The natural chemical and physical variations that occur within volcanic rocks (petrology) provide critical insights into mantle and crust conditions on terrestrial bodies. Visible/near-infrared (VNIR; 0.3-2.5 µm) and thermal infrared (TIR; 5-50 µm) spectroscopy are the main tools available to remotely characterize these materials from satellites in orbit. However, the accuracy of petrologic information that can be gained from spectra when rocks exhibit complex variations in mineralogy, crystallinity, microtexture, and oxidation state occurring together in natural settings is not well constrained. Here, we compare the spectra of a suite of volcanic planetary analog rocks from the Three Sisters, OR to their mineralogy, chemistry, and microtexture from X-ray diffraction, X-ray fluorescence, and electron microprobe analysis. Our results indicate that TIR spectroscopy is an effective petrologic tool in such rocks for modeling bulk mineralogy, crystallinity, and mineral chemistry. Given a library with appropriate glass endmembers, TIR modeling can derive glass abundance with similar accuracy as other major mineral groups and provide first-order estimates of glass wt.% SiO2 in glass-rich samples, but cannot effectively detect variations in microtexture and minor oxide minerals. In contrast, VNIR spectra often yield non-unique mineralogic interpretations due to overlapping absorption bands from olivine, glass, and Fe-bearing plagioclase. In addition, we find that sub-micron oxides hosted in transparent matrix material that are common in fine-grained extrusive rocks can lower albedo and partially to fully suppress mafic absorption bands, leading to very different VNIR spectra in rocks with the same mineralogy and chemistry. Mineralogical interpretations from VNIR spectra should not be treated as rigorous petrologic indicators, but can supplement TIR-based petrology by providing unique constraints on oxide minerals, microtexture, and alteration processes.</p>