Abstract

The tilt of a planet’s spin axis off its orbital axis (“obliquity”) is a basic physical characteristic that plays a central role in determining the planet’s atmospheric circulation, energy redistribution, and climate. Moreover, by strongly enhancing the tidal dissipation rate, planetary obliquities can shape not only the physical features of exoplanets, but also their orbital architectures. Large planetary obliquities can be generated by secular spin-orbit resonances. These occur when the rate of a planet’s spin axis precession matches the rate of its orbital precession. I will present evidence that close-in, compact, Kepler-type systems frequently experience this mechanism – a simple but fascinating result of their intrinsic physical and orbital properties. I will highlight the consequences of this obliquity-driven sculpting by linking it to several strange features of the observed planet population, including the mysterious overabundance of planets wide of mean-motion resonances and the remarkably rapid orbital inspiral of the highly inflated hot Jupiter, WASP-12b.