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The organic inventories of carbonaceous chondrites (CCs) provide insights into the physicochemical environments involved in the formation of the Solar System and the post-accretionary evolution of meteorite parent bodies. Studying changes in these inventories across samples that have experienced varying degrees of aqueous/hydrothermal alteration untangles one aspect of such complex records. Here, the polycyclic aromatic hydrocarbon (PAH) and heterocyclic aromatic compound (HAC) contents of 15 CCs representing CI1, CM1, CM2, C2u, C3u, and CO3 classes were probed with two-step laser mass spectrometry (L2MS) and subjected to a comparative analysis using PCA, a multivariate analysis method. PAHs with mass-to-charge ratios (m/z) of 116 to > 300 were detected, with large PAHs (4-6 rings) dominating the spectra of the most aqueously altered samples like Ivuna (CI1) and NWA 12328 (CM1), while a larger relative fraction of smaller PAHs (3 rings) was observed in relatively unaltered samples like Chwichiya 002 (C3.00u). The same gradual trend was observed across CM2 samples with varying degrees of aqueous alteration with the exception of Jbilet Winselwan (CM2.3-2.5), which has experienced impact shock. Alkylated homologs of C14H10 and C16H10 were detected in all samples, the latter showing a stronger correlation with aqueous alteration. Additionally, oxygen-containing PAHs and thiophenes were detected. These experiments demonstrate that aqueous alteration generally increases the size and alkylation of PAHs in CCs of multiple chemical groups. Thus, secondary alteration significantly alters the PAH contents of CCs, and PAH size distributions in particular may be an additional parameter to consider when evaluating a meteorite's alteration history.

We generated a series of 15 particulate San Carlos olivine samples with varying porosity and particle size. We created five different particle size distributions and each particle size distribution was prepared with three different packing techniques. These samples were then imaged under a microscope and a binarization thresholding technique was used to determine each sample's surface porosity by the ratio of dark, void pixels to the total number of pixels in each image. Our results show that we could estimate surface porosity from the analysis of a microscopic image, a non-destructive technique. These samples were then placed in the Planetary Analogue Surface Chamber for Asteroid and Lunar Environments (PASCALE) and their thermal infrared (TIR) emissivity spectra were measured under ambient or Earth-like conditions. We selected key diagnostic spectral features and compared how these features changed with increased porosity and reduced particle size. From this investigation, we concluded that the spectral effects due to surface porosity and particle size could only be uniquely distinguished from one another when we observed shifts in the transparency feature due solely to changes in porosity.

The rotational and secular light curve of the comet 2P/Encke has been a matter of debate for some decades. Understanding of the rotational properties is fundamental to deriving information on the interior structure of comets, which in turn has implications for solar system formation and evolution. Encke is one of the best observed comets throughout history and yet these basic properties have been highly elusive. While the basic rotational period is broadly known to be approximately 11 hours, it seems to change by almost 1 percent per orbit, and the cause of the unusual single-peaked rotational light curve morphology, which could be attributed to the shape of the nucleus, complex rotation, variable albedo across the surface or a combination of those factors, has been similarly difficult to pin down. Here we present a comparison between optical and mid-Infrared light curves of Encke obtained in 2005, ruling out albedo variations and arguing for a period of 11.03 hours. Furthermore, radial profile analyses indicate that the unexpected brightness near aphelion cannot be attributed to more than 20 percent extended emission and the nucleus does truly resemble a point source.

Atmospheric retrieval is the inverse modeling method where atmospheric properties are constrained based on measured spectra. Due to the low signal-to-noise ratios of exoplanet observations, exoplanetary retrieval codes pair a radiative transfer (RT) simulator with a Bayesian statistical framework in order to characterize the distribution of atmospheric parameters that could explain the observations (the posterior distribution). This requires on the order of 106 RT model evaluations, which requires hours to days of compute time depending on model complexity. In this work, I investigate atmospheric retrieval methods and apply them to observations of hot Jupiters. Chapter 2 presents a set of RT and retrieval tests to validate the Bayesian Atmospheric Radiative Transfer (BART) retrieval code and applies BART to the emission spectrum of HD 189733 b. Chapter 3 investigates the dayside atmosphere of WASP-12b and resolves a tension in the literature over its composition. Chapter 4 introduces a machine learning direct retrieval framework which spawns virtual machines, generates spectra, trains neural networks, and performs atmospheric retrievals using trained neural networks. Chapter 5 builds on this and presents a machine learning indirect retrieval method, where the retrieval is performed using a neural network surrogate model for RT within a Bayesian framework, and compares it with BART. Chapter 6 utilizes the neural network surrogate modeling approach for thermochemical equilibrium chemistry models and compares it with other equilibrium estimation methods. Appendices address retrieval errors induced by choice of wavenumber gridding for opacity-sampling RT schemes, neural network model selection, the effects of data set size on neural network training, and the accuracy of Bayesian frameworks used for atmospheric retrieval.

Primitive asteroids have remained mostly unprocessed since their formation, and the study of these populations has implications about the conditions of the early solar system and the evolution of the asteroid belt. This spectroscopic study of inner main-belt (IMB) primitive asteroids addresses three central objectives: 1) determine the origin and composition of objects in the near-Earth object population, particularly spacecraft targets; 2) test theories of how processes such as space weathering and aqueous alteration affect surface properties of small, low-albedo bodies; and 3) explore how primitive objects in the background population (i.e., asteroids not belonging to dynamical families) relate to each other and their implications for the evolution of the asteroid belt. In this work, I use the NASA Infrared Telescope Facility and the Telescopio Nazionale Galileo to obtain near-infrared (NIR; 0.7 to 2.5 microns) spectra of objects from three families and the background population. I compare the sample spectra with the published spectra of near-Earth objects and dynamical studies to test arguments for origin. I compare the VNIR spectra with laboratory spectra of meteorites to constrain the asteroid compositions. I test for space-weathering effects by comparing the spectra of the younger families with the older, more-weathered families. I look for trends between the spectra of objects in the background family and their physical and orbital properties to uncover information about this primordial population at the time of formation and throughout its evolution. Chapter 3 describes the NIR characterization of the Klio family. Chapter 4 describes the NIR characterization of the Chaldaea family and its relationship to the Klio family. In Chapter 5, I characterize the Sulamitis family and compare with the Polana family. Finally, in Chapter 6 I characterize the primitive background population and compare the background objects with the families at similar locations.

The primary objective of this research is to characterize the surface composition of five comet-asteroid transition objects via near-infrared spectroscopy. The five targets include two asteroids with Tisserand invariants lower than 3.0 (1373 Cincinnati and 2906 Caltech), one asteroid that is likely an extinct comet (944 Hidalgo), one intermittent activity comet (162P/Siding Spring), and one nearly dormant comet (28P/Neujmin1). Previous research regarding cometary end states and dynamical and physical properties of comets and asteroids provides the foundation for this work. Focusing primarily on the 1-2.5 µm spectral region of the five target objects, this project specifically searches for mineral species such as olivine, pyroxene, hydrated silicates, and organics. Comparisons are made with comets, main belt asteroids, and Trojan asteroids. All our targets have near-infrared spectra with varying "red" slopes from S'=1.7 to 5.3. Slopes in this range are characteristic of both primitive asteroids and comets. Three of our objects, 944 Hidalgo, 162P/Siding Spring, 28P/Neujmin 1, showed relatively featureless near-infrared spectra. The two objects dynamically most likely to be of asteroidal origin, 1373 Cincinnati and 2906 Caltech, both displayed features in the 0.8 to 2.5 micron range, not present in any of our other targets or the comparison cometary nuclei. Spectra of 944 Hidalgo were acquired at several rotational phases and clear rotational variations were found. Hints of spectral variability were also observed in 28P/Neujmin 1 and 162P/Siding Spring. Neither 1373 nor 2906 were examined for rotational variability. Based on our results, we believe that 1373 Cincinnatti and 2906 Caltech are not cometary. The spectral range of our targets and cometary spectra in the near-infrared is the same as that of Trojan asteroids. Recommendations for future investigation are suggested.

We present results from a continuing effort to understand activity drivers for the enigmatic Comet 29P/Schwassmann-Wachmann 1 (SW1). SW1 has been of interest since its discovery almost 100 years ago because of its nearly continuous, quiescent activity beyond the water-sublimation line and its highly variable, outburst activity while receiving a nearly constant insolation due to its low eccentricity orbit. These characteristics make SW1 a useful target for investigating both distant cometary activity drivers and also cometary outburst behavior. We approach answering these questions through a detailed analysis of SW1; first by measuring nucleus properties required for a more accurate nucleus thermophysical modeling and second, by applying thermal modeling to replicate its activity. Our project began with an analysis of Spitzer Space Telescope infrared observations of SW1 from 2003. Coma removal techniques when applied to the images provided nucleus photometry measurements. Application of the Near Earth Asteroid Thermal Model (NEATM) to these measured photometry values resulted in an effective nucleus radius of 32.3 ± 3.1 km and a thermal beaming parameter of 1.14 ± 0:22. These results indicated that SW1 is one of the largest Jupiter Family Comets and also has a relatively smooth overall surface and/or a low thermal inertia. We next placed constraints on the nucleus' spin state through analysis of evolution seen in the coma's morphological structure through two sets of outburst coma observations. The first set analyzed are from the Kitt Peak 2.1-m telescope taken ± 2 days after a major outburst in 2008. 3-D Monte Carlo coma modeling showed that the nucleus' spin period is on the order of days and/or the spin pole orientation was along the Earth's directions during observations. The second set are Hubble Space Telescope observations from 1996 taken ± 15 hours after a major outburst. Modeling similarly showed a rotation period on the order of days. Due to the observing geometry differing between the 2008 and 1996 observations, we conclude the rotation period lower limit must be on the order of days even if the spin-pole direction was directed along the sub-Earth direction during one set of observations. The nucleus properties measured or constrained by our project were incorporated into a thermophysical model to replicate the quiescent activity via the sublimation of the supervolatile species CO or CO2. A progenitor nucleus was thermally evolved in SW1's current orbit using different plausible nucleus interior compositional and layering schemes. We discuss results of this analysis and additionally possibilities for future thermal modeling efforts.

<p>A series of elastic x-ray and inelastic neutron experiments have been conducted on La_2-xBa_xCuO₄ (LBCO) crystals for 0 <= x <= 0.35. We find that the dynamic correlations in the system are gapless and persist to at least order Kelvin temperatures. These features display qualitative and quantitative similarity to its sister compound La_2-xSr_xCuO₄ (LSCO) for the same doping. We also find evidence that suggests connection between the dynamic rods of scattering and the pseudogap phase found in these materials, though nothing conclusive can be said at present . We will explore the doping, temperature and energy dependence of these dynamic features in detail.</p> / Master of Science (MS)