Dr. Scott Tremaine, Institute for Advanced Study/University of Toronto
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Abstract: Comets have inspired awe since prehistoric times, but even today there are only a few thousand comets with well-determined orbits. Nevertheless, the analysis of this limited sample yields a compelling model for the formation, evolution, and present distribution of comets. This model implies that the primary source of comets is the Oort cloud, containing over 100 billion comets at 5,000 to 50,000 times the Earth-Sun distance. I will review our current understanding of the structure and formation of the Oort cloud, and what comets can tell us about possible undiscovered planets beyond Neptune. Finally, I'll describe some of the puzzles arising from the recent discoveries of two interstellar asteroids/comets.