abstract: During the early Solar System many physiochemical processes were taking place that would shape the formation and evolution of rocky bodies. Growth of these rocky objects was rapid, with some growing to sizes of 10s – 1000s km (“planetesimals”) in the first few million years. Because these objects formed early, they contained sufficient 26Al (an isotope of Al with a short half-life of ~705,000 yrs) to heat the interiors to melting temperatures, resulting in the formation of the first igneous rocks in nascent Solar System. Depending on the size and time of accretion, some bodies experienced high degrees of melting (with some having global magma oceans) while others experienced lower degrees of partial melting, and yet others did not experience any melting at all. These varying degrees of heating and melting processes on early-formed planetesimals produced a variety of achondritic meteorite types. These achondrites have bulk compositions ranging from ultramafic to basaltic, with some rare types having more highly “evolved” (i.e., high-SiO2) compositions. Determining the detailed chronology of their formation with fine time resolution is key for understanding the earliest stages of planet formation, and there are high resolution chronometers that are ideally suited for this application. Three such chronometers (i.e., the 26Al-26Mg, 53Mn-53Cr, and 207Pb-206Pb chronometers) are the focus of this work. Based on investigations of these chronometers in several achondritic meteorites, the implications for the formation and evolution of planetesimals in the early Solar System will be discussed. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

Les météorites sont parmi les sources d’information les plus importantes sur la structure et l’évolution du système solaire. Cette thèse présente une étude des météorites d’Iran, en particulier celles retrouvées dans le désert de Lut et leur comparaisons avec celles des autres déserts chauds du monde. Les météorites de Lut sont étudiées en détail en vu de comprendre le potentiel de ce désert dans l’accommodation et la classification des météorites, les âges terrestres, la météorisation, distribution spatiale et ‘pairing’. Nous démontrons la présence de deux champs de strewnfields de météorites et mettons en évidence les conditions favorables à la conservation, accumulation et collection des météorites. Nos données révèlent les différences entre les effets chimiques et minéralogiques de le météorisation (l’altération) sur les météorites en provenance de différents déserts. Parmi les centaines de météorites classifiées des déserts chauds, nous présentons notre étude détaillée sur un chondrite non-classifié (El Médano 301). Cette météorite, pourrait représenter un nouveau sous-groupe des chondrites ordinaire (OCs) avec une composition chimique moins réduite par rapport aux OCs standards. Famenin et Moshampa, deux météorites tombées en été 2015 dans le nord-ouest d’Iran, sont également étudiées en détail. Famenin est un chondrite ordinaire de type 3 qui présente des charactéristiques intermédiaires entre les chondrites H et L. Enfin, nous présentons les résultats de notre étude sur la météorite de Moshampa qui est une chondrite brecciated de type LL5. / Meteorites are amongst the most important sources of information about the structure, formation, and evolution of the solar system. This thesis reports studies on the meteorites from Iran, in particular the Lut desert and their comparison with the meteorites from other hot deserts. Lut desert meteorites are studied in detail to understand the potential of this desert for hosting meteorites, meteorite classification, terrestrial ages, terrestrial weathering, spatial distribution and pairing. We shows the presence of two main meteorite strewnfields and evidence suitable conditions for preservation, accumulation and finding of meteorites. Meteorites from different hot deserts are studied in order to document meteorite abundances, classification, and their terrestrial alteration. Our data reveal differences between the chemical and mineralogical effects of terrestrial weathering on meteorites from different deserts. Among the hundreds of classified hot desert meteorites, we present a detailed study on an ungrouped chondrite (El Médano 301). This meteorite might be representative of a new grouplet of ordinary chondrites (OCs) showing more reduced compositions than standard OCs. Famenin and Moshampa, two meteorites fallen during summer 2015 in NW Iran, are studied in detail. Famenin is a type 3 ordinary chondrite showing characteristics intermediate between H and L chondrites. Together with similar intermediate meteorites, we suggest the existence of a separate ordinary chondrite grouplet for which a different designation (H^L) is proposed. Classification results of Moshampa brecciated LL5 chondrite are reported.

Our inventory of material from the early solar system includes large, igneous-textured inclusions in O chondrites, whose origin and relationship to their host meteorite is unclear. These inclusions occur in approximately 4% of O chondrites, and are mineralogically, petrographically, and chemically diverse. Petrographic and chemical data from 29 inclusions from 23 host meteorites were collected with optical light and scanning electron microscopy, allowing for the determination of major phase modal abundance and major element bulk chemistry. No correlation between any inclusion property and host meteorite type were found, but some trends were observed. Nine of the inclusions show strong evidence, such as radial variations in texture and chemistry, for having crystallized as a free-floating droplet in a space environment, and may share the same formation process as chondrules. One inclusion is almost certainly shock-melted material that intruded into the host material. Thirteen inclusions have bulk chemistry patterns that suggest the material was vapor fractionated; the remaining sixteen are essentially chondritic, i.e., unfractionated. Broadly, the data support the conclusions of Ruzicka et al. (1998, 2000), which divided large inclusions into Na-poor (vapor fractionated) and Na-rich (unfractionated) groups, suggesting at least two different origins. There is no evidence that any of the inclusions studied formed by igneous differentiation.

The recent discovery of objects near the 5:1 Neptune resonance prompts the study of the size, structure, and surface properties of this population to determine if these parameters are consistent with a ‘Nice model’ type evolution of the outer Solar System. Previous TNO discovery surveys have primarily targeted the ecliptic plane, where discovery of high inclination objects such as the 5:1 resonators is unlikely, and theoretical work on the evolution of the outer Solar System has focused on structure in and around the main Kuiper belt and largely ignored the distant resonant TNOs. I tracked these objects for several semesters, measured their positions accurately, and determined precise orbits. Integrating these orbits forward in time revealed that three objects are 5:1 resonators, and one object is not resonant but may have been resonant in the past. I constrained the structure of the 5:1 resonance population based on the three detections and determined that the minimum population in this resonance was much larger than expected, 1900(+3300,−1400) with H < 8. I compared this large population with the orbital distribution of TNOs resulting from a Nice model evolution and determined that the population in the real 5:1 resonance is ~20–100 times larger than the model predicts. However, the structure of the 5:1 resonance in this model was consistent with the orbital distribution I determined based on the detections. The orbital distribution of the scattering population in the Nice model is consistent with other models and survey results, leading to the conclusion that the 5:1 resonance cannot be a steady state transient population produced via resonance sticking from the scattering objects. To test the origin of the 5:1 resonators, I measured the objects’ surface colors in multiple wavelength ranges and compared their surface reflectance to TNOs from a large color survey, ColOSSOS. The 5:1 resonators have a consistent selection criteria to the TNOs from the ColOSSOS survey, so these samples have known selection biases and can be usefully compared to each other. The surfaces of the three 5:1 resonators showed three different spectral reflectance shapes, indicating that these three objects do not share a common formation location. The surface properties and orbital distribution of current 5:1 resonators are consistent with the remnant of a large captured population, partially resupplied by the scattering objects. However, the scattering event which produced this large 5:1 population remains unexplained. / Graduate

Jupiter Trojan asteroid dynamics have been studied for a long time but it is only within the last decades that the known population has become large enough to make other studies meaningful. In four articles I have been scratching the surface of the unknown Trojan knowledge space. Paper I presents photometric observations confirming a larger variety in surface redness for the smaller Trojans compared to the larger ones, in line with the groups in the outer main asteroid belt. However, the largest Trojans are significantly redder compared to the largest Cybele and Hilda asteroids. Paper II is an investigation of the Trojan discovery completeness. The analysis shows that all Trojans down to a limiting absolute magnitude of H=11.5 mag have been discovered. Missing Trojans in the almost discovery-completed section should have inclinations above the mean of the same group. The faintest Trojans are discovery biased due to orbit orientations similar to the Milky Way. Paper III is a general review of dynamical and physical properties of the discovery-completed sample of Jupiter Trojans found in Paper II. The two Trojan swarms are often treated as being equal, but are different in a number of details. Two known facts are that the L5 swarm is less rich, while the L4 swarm has a larger fraction of low inclination Trojans. Trojans are in general red objects but the mean redness is higher for Trojans which have not collided compared to Trojans in families. Paper IIII is an investigation of Trojan collisions, family detection and evolution. Collision circumstances were mapped using numerical simulations and recorded Trojan close approaches. Synthetic families were created and evolved numerically. The result suggests that the HCM family detection technique can find Trojan families even in a densely populated parameter space. However, interlopers cannot be avoided at any level but their contribution should be less than 30%. Synthetic families can be identified with backwards orbital integrations for times up to a Gyr-scale. However, there are discrepancies between real Trojan families and my synthetic families.

The Kuiper belt is a population of small bodies located outside Neptune's orbit. The observed Kuiper belt objects (KBOs) can be divided into several subclasses based on their dynamical structure. I construct models for these subclasses and use numerical integrations to investigate their long-term evolution. I use these models to quantify the connection between the Kuiper belt and the Centaurs (objects whose orbits cross the orbits of the giant planets) and the short-period comets in the inner solar system. I discuss how these connections could be used to determine the physical properties of KBOs and what future observations could conclusively link the comets and Centaurs to specific Kuiper belt subclasses. The Kuiper belt's structure is determined by a combination of long-term evolution and its formation history. The large eccentricities and inclinations of some KBOs and the prevalence of KBOs in mean motion resonances with Neptune are evidence that much of the Kuiper belt's structure originated during the solar system's epoch of giant planet migration; planet migration can sculpt the Kuiper belt's scattered disk, capture objects into mean motion resonances, and dynamically excite KBOs. Different models for planet migration predict different formation locations for the subclasses of the Kuiper belt, which might result in different size distributions and compositions between the subclasses; the high-inclination portion of the classical Kuiper belt is hypothesized to have formed closer to the Sun than the low-inclination classical Kuiper belt. I use my model of the classical Kuiper belt to show that these two populations remain largely dynamically separate over long timescales, so primordial physical differences could be maintained until the present day.The current Kuiper belt is much less massive than the total mass required to form its largest members. It must have undergone a mass depletion event, which is likely related to planet migration. The Haumea collisional family dates from the end of this process. I apply long-term evolution to family formation models and determine how they can be observationally tested. Understanding the Haumea family's formation could shed light on the nature of the mass depletion event.

The purpose of this study is to develop an understanding of the observability of small-scale dynamical Solar System features in meteor orbit radar data, particularly with reference to mean motion resonance effects. Particular focus is placed on the presence of `resonant swarms' in meteoroid streams: the resonant swarm at the 7:2 Jovian mean-motion resonance is used as an example, as it best satisfies radar observability criterion. Furthermore, evidence for this structure exists in visual meteor data. The radar dataset used for this study is that of the Canadian Meteor Orbit Radar (CMOR) as this dataset contains the largest number of meteoroid stream particles. The aim here is to determine whether the Taurid resonant swarm is observable in datasets produced by radars such as CMOR, or what improvements in individual orbital uncertainties are necessary for positive detection to be possible. The observability of the Taurid swarm in radar data depends on the limitations of the radar data (in terms of the individual measurement uncertainties); and on the properties of the resonance itself. Both aspects are investigated in this thesis. A statistical study is first conducted to assess whether evidence for the swarm exists in a dataset containing CMOR Northern and Southern Taurids from the years 2002 to 2007. It is found that the level of variations present is consistent with that expected due to random fluctuations: there is no evidence for a statistically significant resonant feature at the location of the 7:2 Jovian resonance. Additionally, the observability of various sizes of resonant peak for different sizes of dataset and for different levels of measurement uncertainties is investigated by addition of a modelled resonant feature to the data, followed by replacement of individual meteors by Gaussian profiles to simulate the effect of orbital uncertainties. It is clear that the level of broadening resulting from the uncertainties of the CMOR data used will not allow the observation of a resonant peak of the expected size. Detection is expected to be more likely in a `swarm encounter year' (a year in which the geometry between the resonant swarm and Earth is favourable to detection). The velocity uncertainties of a meteor orbit radar (similar to CMOR) need to be improved by a factor of 5 to 10 (relative to the CMOR uncertainties) in order to detect a resonant swarm that is composed of ~30% to ~5% (respectively) of the total number of observed Taurids in a swarm encounter year. An improvement significantly greater than a factor of ~10 is unlikely to result in a significant improvement in the ability to detect the resonant swarm. It is expected that a factor of 10 improvement in radar measurement uncertainties is achievable with the current techniques of radar systems and signal processing. These statistical tests require knowledge of the resonant width of the 7:2 Jovian resonance in semi-major axis, as this provides the size of the resonant feature of interest. Such resonant or libration widths can be determined analytically for orbits with low eccentricities. As Taurid orbits have high eccentricities (e~0.83), a hierarchical N-body integrator is used to examine the dynamics in the region of the 7:2 resonance, and determine a resonant width of (0.047±0.005) AU. To verify this method the standard analytic equations and a semi-analytic method are compared (at low eccentricities) with the numerical resonant width values: the agreement is within 10% for eccentricities below 0.4. It is important to know what proportion of radar Taurids are expected to be resonant in a swarm year in order to evaluate the observability of the swarm in radar data. One important factor that may affect this is the mass distribution of particles in the swarm. This is investigated by ejecting particles in multiple directions from three model comets: the first with a mass and orbit in agreement with those of the current 2P/Encke; the second with 2P/Encke mass and an orbit matching that of the proposed proto-Encke object; and a third with the mass and orbit of proto-Encke. The resulting orbits are examined to determine what proportion will land within the 7:2 resonance, for a range of particle masses and densities. The instantaneous effect of radiation pressure on the orbits of ejected particles is also considered. However, it is difficult to determine accurate capture percentage values due to the uncertainty surrounding cometary ejection mechanisms. Nevertheless, it is found that capture of Taurids into the 7:2 resonance by all comets is possible. Using comparisons between the percentages of visual-sized and radar-sized particles captured, it is determined that in weak swarm years (in which only 20% of visual meteoroids detected are resonant) only 4% to 5% of observed visual Taurids are expected to be resonant. Such a swarm would be on the edge of observability. However, in stronger swarm years (such as 2005), the resonant proportion will exceed that required for detection with a reduction in CMOR measurement uncertainties of a factor of ten.

Ultra-wide Trans-Neptunian Binaries (TNBs) are extremely sensitive to perturbation, and therefore make excellent probes of the past and present dynamical environment of the outer Solar System. Using data gathered from a host of facilities we have determined the mutual orbits for a sample of seven wide TNBs whose periods exceed one year. This characterized sample provides us with new information about the probable formation scenarios of TNBs, and has significant implications for the early dynamical and collisional history of the Kuiper Belt. We show that these wide binaries have short collisional lifetimes, and use them to produce a new estimate of the number of small (~1 km) objects in the Kuiper Belt. Additionally, these systems are susceptible to tidal disruption, and we show that it is unlikely that they were ever subjected to a period of close encounters with the giant planets. We find that the current properties of these ultra-wide Trans-Neptunian Binaries suggest that planetesimal growth in the Cold Classical Kuiper Belt did not occur through slow hierarchical accretion, but rather through rapid gravitational collapse. / Graduate

Thesis (Ph.D.)--Murdoch University, 2003. / Thesis submitted to the Division of Science and Engineering. Bibliography: leaves 255-267.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 115-124).