New Frontiers for Comparative Exoplanetology In the Era of Kepler

Statistical surveys and individual characterization are the keys to addressing the fundamental questions in exoplanetology. Thanks to the Kepler mission, there is now a menagerie of new transiting planets that are very different in terms of their physical properties (often cooler) compared to the classical close-in hot giant planets. This laboratory provides an excellent opportunity to characterize the atmospheres of planets in new regimes, and to study those planets that have experienced different formation, evolution and migration scenarios compared to hot-Jupiters. We propose to initiate a comparative exoplanetology survey program using the two existing main classes of known transiting giant planets: the hot-jupiters orbiting bright host stars for which we can obtain precise atmospheric constraints, and the confirmed Kepler giant planets that provide us with the opportunity to probe new regions of planetary parameter space. We have identified two dozen representative giant planets (some are in multiple systems) which are excellent candidates in achieving our scientific goals. Our strategy will be to combine Spitzer observations with a wealth of multi-wavelength transmission spectroscopic measurements that we are currently gathering. This powerful, already tested method has constrained atmospheric compositions of exoplanets through the measurement of their scale height. The strength of this approach is to combine observations which cover a wide spectral range and which are, therefore, sensitive to different atmospheric compositions and structures. Within this framework, Spitzer observations provide the key to achieving the science goals of our program; this is the only facility that can reach the photometric precision required to probe the main atmospheric molecular features (H2O, CH4, and CO) that dominate the Infrared spectrum. Our survey will be the largest and the statistically most complete atmospheric program, two prerequisites necessary to make major progress in exoplanetology.