Astronomy Colloquium

Laplace argued, correctly, that the small inclinations of planetary orbits implied that the solar system formed from a flat disk.  The evidence on whether extrasolar planetary systems are flat, however, is still ambiguous. I will describe (i) measurements of the Rossiter-McLaughlin effect in transiting planets, which show that many planetary systems have large stellar obliquities (angle between the stellar spin angular momentum and planetary orbital angular momentum); (ii) the curious phenomenon of Kozai-Lidov oscillations and their role in exciting eccentricities, inclinations, and obliquities; (iii) constraints on the flatness of planetary systems from the Kepler spacecraft and other sources; (iv) disk and high-eccentricity migration as competing mechanisms for the formation of hot Jupiters.