Exoplanets and Cosmic Habitability
Jonathan Fortney, University of California Santa Cruz
Large ground-based telescopes and NASA’s Kepler Space Telescope have now shown us that extrasolar planets (or “exoplanets”) are common in our galaxy, at a wide range of planet sizes and orbital distances from their parent stars. For the subset of these planets that are both 1) similar in size to the Earth (and are hence thought be rocky), and 2) that receive levels of incident starlight comparable to that of Earth (perhaps yielding Earth-like surface temperatures), the number is tens of billions within the Milky Way. 20 years ago there was no way to know if planets were common, but now that is an answered question.
But what do we know about these potentially Earth-like exoplanets, and how do we find them? I will discuss the numerous methods that astronomers have developed to find exoplanets, and what kinds of planets can and cannot be found by these methods. The strengths and weaknesses of these methods can bias our view of what kinds of planets are out there. I will discuss the current state of the art in characterizing the atmospheres of exoplanets, which now entirely focuses on larger, less Earth-like worlds, which are easier to observe. I will also discuss the relatively crude metrics that astronomers use when trying to assess whether planets may be potentially habitable, given our lack of detailed information about them.