Thesis (Ph.D.) - Rijksuniversiteit Groningen (Netherlands), 2009.

Comets and Centaurs are icy remnants from the formation of the solar system. Analyzing the physical properties of their nuclei and their production rates can serve as powerful tools for tracing primitive solar system material. The four research projects in this dissertation examine these properties in comets and Centaurs. The first project focuses on observations of main belt comet 176P/LINEAR that were obtained with the Kepler space telescope. Optical lightcurves were used to constrain models of the nucleus's spin pole axis, shape and activity level. The second project used millimeter-wavelength spectra from the Arizona Radio Observatory Submillimeter Telescope and infrared photometry of Spitzer images to derive production rates of CO and CO2 from Oort Cloud comet C/2016 R2 (PANSTARRS). The third project is a compendium of CO, CO2, and H2O production rates in more than 25 comets and Centaurs that were obtained with a variety of space-based and ground-based telescopes and which were analyzed to test models of comet formation and evolution. CO, CO2, and H2O are the most abundant molecules observed in comets. The combination of these three molecules are likely the largest sources of elemental oxygen in the gas comae of comet and therefore a close approximation of the oxygen released in the comae. One key result of the survey is that CO/CO2 production rate ratios appear largely heliocentric dependent, with more CO produced the farther the comet is from the Sun. One exception is dynamically new comets which typically produce more CO2 than CO which is in predicted by models of significant cosmic-ray processing over time. The fourth project produced the first CO2 detection in a Centaur (39P/Oterma), which shows significant differences between the CO/CO2 in 39P and 29P, another Centaur, which may be partly due to different heating and processing histories.

Every scientific experiment or innovation goes through a phase of testing equipment. This is not only true for experiments in the laboratory, but also very relevant for experiments on other planetary bodies. In order to test tools and robotic equipment that are destined for another planet, moon, asteroid or comet, it is necessary to simulate the regolith environment on that surface. In this thesis we have provided an overview of two methods for regolith simulant development. In one approach we made simulants in different compositions to find the best spectral fit to Jupiter Trojan asteroids. At visible to near-infrared (VNIR) wavelengths, the Trojans' spectra have low overall reflectance and red spectral slopes, and a distinctive 10 μm plateau at thermal infrared (TIR) wavelengths. Trojan spectra may be explained by high porosity, fine particulate silicate minerals like olivine mixed with opaques and organics. Our Trojan simulants were made from silicate (olivine), opaque (iron sulfide) and organics (coals) in various proportions and particle sizes. Resulting mixtures were analyzed with spectrometers VNIR to TIR wavelengths. While the perfect Trojan simulant was not created, compositional and particle size effects were characterized, which helps to better understand the Trojan spectra. It is unknown how water ice content changes regolith and dust properties. To be safe during lunar exploration more research and modeling of possible regolith behavior is necessary. The second project presented in this thesis is about a new production method for lunar permanently shadowed regions (PSRs) icy regolith simulant. We build on an existing lunar highlands simulant, by adapting it for lunar poles, where water ice might be present in permanently shadowed regions. We have developed a production pipeline to make granular icy simulant with variable water ice content. We found that icy simulant has an increased porosity, that persists even after dehydration.

Binary asteroid systems make up roughly 15% of objects occupying near-Earth space, the Main Belt, and trans-Neptunian space. The impact history of asteroids in binary systems represents an interesting aspect of the general problem pertaining to the nature and evolution of surfaces for such objects. Specifically, the post-impact dynamics of ejecta and its relation to surface modification is a challenging question owing, in part, to the unusual gravitational field in a binary system and the subsequent capture and emplacement of debris on either binary component. Observable differences or similarities between the two bodies in the color, reflectance, thermal properties, and grain properties of their respective regoliths could give insight into the system's past and the circumstances of recent impacts. Here we present simulations of impact scenarios in a wide variety of binary systems in order to generate a large family of prediction models for resurfacing and ejecta covering outcomes due to impacts. In this way, we can address our main science question of how specific binary system parameters influence the evolution of their surfaces. To create a library of ejecta outcomes, we first developed the Rebound Ejecta Dynamics (RED) package (Larson and Sarid 2021), an N-body integrator designed to model post-impact debris dynamics that builds on the existing Rebound software (Rein and Tamayo 2015). This package allows us to vary the many of the important parameters of a binary system, including primary-secondary separation, rotation periods, and mass ratios, as well as impact-related parameters, such as impact surface location, ejecta size and velocity distribution, and ejecta compositions. Our simulations generally use 10,000 particles and cover one week of simulation time. From our simulations, we calculate the percentage of the system that is resurfaced, the distance that particles travel from the impact site, and the percentage of particles that impact the surface. These regions of resurfacing can often be observed with different colors or spectral properties than the original surface. We find that there are trends in ejecta end-states as a function of binary system properties (i.e., primary rotation period and system mass ratio) for several common impact scenarios. We analyzed the dominant effect that influences the outcome of each impact event.

In this dissertation work we sought to answer questions about the age, composition, and origin of planetary bodies. We implemented multiple approaches to answer these questions. To determine the age of the Clarissa asteroid family we implemented a modified version of SWIFT: a Solar System integration software package by Levison & Duncan (1994) to account for gravitational as well as thermal perturbations. This work constrained the age of the Clarissa asteroid family to be 56 ± 6 My. Next, we used a sum to one constraint weighted least squares (STO WLS) modeling approach to model thermal infrared (TIR) spectra of a suite of primitive asteroid analogs spectrally and volumetrically dominated by fine particulates ( < 38 µm). We determined that an alternative approach to the STO WLS model is needed to analyze asteroid regolith when it is dominated by fine particles ( < 90 µm). Our next approach included the Trojan asteroids (911) Agamemnon, (1172) Aneas, and (624) Hektor, and primitive asteroid (944) Hidalgo whose emissivity spectra share a prominent 10 µm plateau that is also present in cometary comae spectra. We used Multiple Sphere T-Matrix (MSTM) and Hapke reflectance models to model the asteroid spectral features using a mixture of olivine components (Mg-rich and Fe-rich olivine), fine particles (~0.5-1.0 µm), and lunar-like porosities (~74-87%). Finally, we used a light scattering Mie and Monte Carlo radiative transfer approach to model ambient (measured under Earth-like conditions) lunar regolith spectra. This study indicates that additional work needs to be done to develop an integrated thermal and light-scattering model that can replicate the effects of the thermal gradient present under lunar environment conditions because a light-scattering model alone is not able to reproduce the observed changes in the spectra that we see with space weathering.

Transiting exoplanets provide the best opportunity for planetary characterization, and thus the search for life outside the Solar System. These planets orbit such that they pass in front ("transit'') and behind ("eclipse'') their host star, and a spectrum of the lost flux constrains the atmospheric properties of the planet. In transits, the flux modulation scales with the cross-sectional area of the planet, and the spectrum includes signatures of molecules in the upper atmosphere of the planet's terminator, which the host star's light passes through on the way to the observer. With eclipses, the lost flux is the direct emission of the planet, a spectrum of which contains emission and absorption features of molecules in the atmosphere depending on atmospheric thermal structure. These signals scale with the size and brightness of the planet and are so dwarfed by the brightness of the host star that only > 1000 K Jupiter-sized planets are observable with current instrumentation. In this work, I develop new techniques and compare existing data analysis methods to extract weak planetary signals. Chapter 2 describes a new elliptical photometry data analysis approach to disentangle exoplanet observations from telescope vibrations. Chapter 3 describes an analysis of Spitzer Space Telescope observations of eclipses of the planet WASP-29b using elliptical photometry and two different light curve modeling methods, and addresses the differences between results. In Chapter 4, I analyze two similar observations of WASP-34b using a grazing eclipse light-curve model. Finally, in Chapter 5 I reanalyze all Spitzer eclipse observations of the Neptune-sized GJ 436b, applying the lessons learned from my earlier works, and comparing my results with the literature.

The Almahata Sitta meteorites produced from the breakup of 2008 TC3 were highly unusual, as the stones contained various meteorite types, with stones spanning almost every meteorite petrologic type. This was considered a remarkable event at the time since meteorites of different types had never been found among the same fall before. However, new discoveries of exogenous material on (4) Vesta, (101955) Bennu, and (162173) Ryugu in subsequent years imply that this event may be more common than initially thought. This is unexpected due to the high average collisional velocity in the asteroid belt of ~5 km/s. High velocity impacts are more likely to have low impact retention efficiencies, which lowers the likelihood of xenoliths surviving the collision. Our understanding of this material and the mechanisms by which it is delivered can give insights into the dynamic histories of these asteroids and even the greater dynamic history of the asteroid belt.

Most small asteroids are defined as "rubble-piles," or bodies with zero tensile strength and large bulk porosity that are tenuously held together by cohesive forces. Improving the accuracy of predictions of asteroid strengths requires suitable laboratory measurements of relevant materials, as well as increasing the availability of materials from sample return. In this work, we use Atomic Force Microscopy (AFM) force measurements and particle characterization to characterize, evaluate, and decouple variables that affect cohesive forces that act between micron-sized grains. In our first investigation we explored interactions of JSC-1 lunar simulant grains using three sample sizes, three spherical AFM tip diameters, and varying relative humidity, observing that the results are very dependent on the RH and, by proxy, adsorbed water. We observed weaker adhesion with larger grain/tip size, which can be attributed to the changing contact area between the samples and the tips. We next performed experiments in vacuum conditions and characterized the cohesive values of a high-fidelity CI simulant (Exolith) based on the CI1 meteorite Orgueil. Our results show no significant trend in adhesion, but we do observe that some correlating characteristics of the grains, such as roughness, can dominate the work of adhesion. The chemical nature of the grains, including their affinity for water, also played a role in if they became more adhesive in vacuum conditions or less adhesive in vacuum conditions. Our studies decouple several factors that contribute to the complex physics of adhesion and even more complex idea of understanding adhesion in a space environment with irregularly shaped grains. This approach will pave the way to a better understanding of regolith surface properties, improve contact models for irregularly shaped particles, and provide suitable inputs for models of asteroid cohesion. This analysis technique can be used on future materials provided by sample return missions.

<p>The gravitational collapse of a giant molecular cloud produces localized dense regions, called clumps, within which low-mass star formation is believed to occur. Recent studies have shown that limitations of current observing techniques make it difficult to correctly identify and measure properties of these clumps that reflect the true nature of the star-forming regions. In order to make a direct comparison with observations, we produced synthetic column density maps and a spectral-line cube from the simulated collapse of a large 5000 solar mass molecular cloud. The synthetic observations provide us with the means to study the formation of star-forming clumps and cores in our simulation using methods typically used by observers. Since we also have the full 3D simulation, we are able to provide a direct comparison of `observed' and `real' star-forming objects, highlighting any discrepancies in their physical properties, including the fraction of cores which are gravitationally bound. We have accomplished this by studying the global properties of the star-forming objects, in addition to performing a direct correlation of individual objects to determine the error in the observed mass estimates. By correlating the clumps found in the simulation to those found in the synthetic observations, we find that the properties of objects derived from the spectral-line data cube were more representative of the true physical properties of the clumps, due to effects of projection greatly impacting the estimates of clump properties derived from two-dimensional column density maps.</p> / Master of Science (MSc)

<p>A deep, wide-field survey was conducted to hunt for the light echo systems associated with SN 1054 (Crab) and SN 1181 as an initial step to acquiring spectra and the prospect of extracting lightcurves of these historical, core-collapse supernovae. Images were acquired by the Canada-France-Hawaii Telescope’s MegaCam during the 2011A and 2011B semesters for fields adjacent to SN 1054 and SN 1181, respectively. A total of 367 Sloan g’ fields for the Crab and 195 Sloan r’ fields for SN 1181 were imaged twice, with a minimum of one month separation.</p> <p>Examination of 13,880 and 11,052 difference images for the Crab and SN 1181, respectively, revealed no light echoes with surface brightnesses brighter than 24.0 mag/arcsec² (the threshold for being able to acquire useful spectra). Based on our non-detections and assuming similar dust properties to nearby (detected) supernova light echo systems (Tycho and Cas A), we conclude it is unlikely that either SN was a Type II-L outburst but cannot provide constraints on other sub-types.</p> <p>We further examined the known light echo locations for Tycho and Cas A and found a statistically-significant correlation between CO brightness temperature and the presence of scattering dust. However, the spacing of grid points in existing CO surveys is too sparse to be useful even a few degrees away from the galactic plane. We have yet to identify a search strategy based on survey data which is superior than random field placement.</p> / Master of Science (MSc)