Princeton University Extrasolar Planet Discussion Group

Survey missions have identified over 5000 extrasolar planets. This sample has revealed detailed features in the demographics of planet sizes and orbital spacings. However, knowledge of their orbital shapes — a key tracer of planetary formation and evolution — remains far more limited. To unveil the subtle relationships between planetary orbits and other star/planet properties, I have developed a framework for classifying planetary systems according to the complexity of their orbits and diversity of their constituent bodies. Analyses using this framework suggest that planet-planet interactions play an important role in shaping the structure of planetary systems. I also present measurements for the eccentricities of 2000 transiting planets with sizes ranging from 0.5 to 16 Earth-radii (R⊕). On average, large planets (4–16 R⊕) are five times more eccentric than small planets (0.5– 4 R⊕), pointing to distinct formation channels for these two size groups. Small planets form on nearly circular orbits and experience minimal perturbations, while large planet eccentricities are excited more often. Small planets are bifurcated into at least two groups, super-Earths (1.0– 1.5 R⊕) and sub-Neptunes (2.0– 3.0 R⊕), with few planets in between. The planets that fall between these two populations also have elevated eccentricities, pointing to another formation channel that likely involves impacts and mergers.