The flyby of Pluto and Charon by the New Horizons spacecraft provided highresolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters ≲13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (≲1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely ≳4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System. One Sentence Summary: Pluto and Charon crater data reflect the small Kuiper belt object population, constraining models of planetary accretion and evolution.

The Outer Solar System Origins Survey (OSSOS), a wide-field imaging program in 2013-2017 with the CanadaFrance-Hawaii Telescope, surveyed 155 deg 2 of sky to depths of m r = 24.1-25.2. We present 838 outer solar system discoveries that are entirely free of ephemeris bias. This increases the inventory of trans-Neptunian objects (TNOs) with accurately known orbits by nearly 50%. Each minor planet has 20-60 Gaia/Pan-STARRS-calibrated astrometric measurements made over 2-5 oppositions, which allows accurate classification of their orbits within the trans-Neptunian dynamical populations. The populations orbiting in mean-motion resonance with Neptune are key to understanding Neptune's early migration. Our 313 resonant TNOs, including 132 plutinos, triple the available characterized sample and include new occupancy of distant resonances out to semimajor axis a ∼ 130 au. OSSOS doubles the known population of the nonresonant Kuiper Belt, providing 436 TNOs in this region, all with exceptionally high-quality orbits of a uncertainty σ a 0.1%; they show that the belt exists from a  37 au, with a lower perihelion bound of 35au. We confirm the presence of a concentrated low-inclination a ; 44 au "kernel" population and a dynamically cold population extending beyond the 2:1 resonance. We finely quantify the survey's observational biases. Our survey simulator provides a straightforward way to impose these biases on models of the trans-Neptunian orbit distributions, allowing statistical comparison to the discoveries. The OSSOS TNOs, unprecedented in their orbital precision for the size of the sample, are ideal for testing concepts of the history of giant planet migration in the solar system.

Canada's Near-Earth Object Surveillance Satellite (NEOSSat), set to launch in early 2012, will search for and track Near-Earth Objects (NEOs), tuning its search to best detect objects with semimajor axis a < 1.0 AU. In order to construct an optimal pointing strategy for NEOSSat, we needed more detailed information in the a < 1.0 AU region than the best current model (Bottke et al., 2002) provides. We present here the NEOSSat-1.0 NEO orbital distribution model with larger statistics that permit finer resolution and less uncertainty, especially in the a < 1.0 AU region. We find that Amors = 30.1 ± 0.8%, Apollos = 63.3 ± 0.4%, Atens = 5.0 ± 0.3%, Atiras (0.718 < Q < 0.983 AU) = 1.38 ± 0.04%, and Vatiras (0.307 < Q < 0.718 AU) = 0.22 ± 0.03% of the steady-state NEO population, where Q is the orbit's aphelion distance. Vatiras are a previously undiscussed NEO population clearly defined in our integrations, whose orbits lie completely interior to that of Venus. Our integrations also uncovered the unexpected production of retrograde orbits from main-belt asteroid sources; this retrograde NEA population makes up ≃ 0.10% of the steady-state NEO population. The relative NEO impact rate onto Mercury, Venus, and Earth, as well as the normalized distribution of impact speeds, was calculated from the NEOSSat-1.0 orbital model under the assumption of a steady-state. The new model predicts a slightly higher Mercury impact flux. Preface this thesis. Further information concerning the contributions made by Sarah Greenstreet can be found in Appendix B. • Manuscript preparation: The majority of this thesis has been submitted to the scientific journal Icarus for publication. This thesis was written entirely by Sarah Greenstreet with the exception of Section 3.1.2 and portions of Section 3.2, which were written by Dr. Brett Gladman.

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