The Galactic Planetary Census
Dept. of Astronomy and Astrophysics
The past decade has spawned a revolutionary new astronomical field: the study of alien planetary systems. Astronomers have now found nearly 200 extrasolar worlds, which populate planetary systems of astonishing diversity. Many of the first extrasolar planets to be detected were "Hot Jupiters" with orbital periods of only a few days, and eccentric giants, which are Jupiter-sized planets orbiting at distances simular to the Sun-Earth distance. We now also know of frigid worlds only a few times more massive than Earth orbiting red dwarf stars, and bizarre multiple-planet systems that have likely experienced histories rife with planetary close encounters, collisions, and ejections. Extrasolar planets are allowing us to understand how planetary systems form and evolve, and they are allowing us to place our own planetary system into the context of the galactic planetary census. In this talk, I'll explain the mechanisms (transits, radial velocity, microlensing) by which extrasolar planets are detected, and I will give an overall sense of the distribution of planetary properties. I'll argue that within the next ten years, we will know whether systems like our own are common or rare, and that we will almost certainly have specific examples of alien Earths – terrestrial planets orbiting at distances from their parent stars where liquid water, and life can exist.