干旱区生态环境知识资源中心

With almost 400 planets currently known, the study of extrasolar planetary systems has blossomed into a rich field. Still, large classes of planets are predicted to exist but remain to be discovered. Here, I selectively review the state of exoplanetary science and focus on one observationally-driven frontier. Massive planets at wide separations from their host stars have now been directly imaged. I discuss how the interplay between theory and observation at this frontier offers a window into both the phenomenological question of what types of planets and planetary systems exist and the theoretical question of how they came to be.