Exoplanets: Misaligned, Migratory, Metallic, and Mini
The physics of planetary systems has been revealed with new observations, yielding the demise of major paradigms and the detection of new domains in mass, radius, and orbital structures. Spin-orbit alignment between the star and planet is commonly violated, with some planets orbiting retrograde. These misalignments utterly contradict the accepted theory of planet migration in a gaseous protoplanetary disk and differ from our own solar system. Meanwhile, Doppler-detected exoplanets reveal a rapidly rising mass function toward lower masses - all the way to 3 Earth-masses, pointing to the occurrence frequency of Earth-mass planets. The NASA Kepler Mission has discovered 1200 planet candidates with most having diameters less than 5 times that of Earth and some as small as that of Earth. One planet is definitively rocky. The distribution of planet radii rises toward smaller sizes, to at least 1.5 Earth-radii. The implication is that planet-planet interactions and perhaps chaos dominate the structural evolution of planetary systems. The diversity of exoplanets continues to confound, delight, and inform us about planetary systems in general, with our Solar System being just one example.