Princeton University/Institute for Advanced Study Planet/Exoplanet Discussion Group

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 habitability. Moreover, by strongly enhancing the tidal dissipation rate, planetary obliquities can shape not only the physical features of exoplanets, but also their orbital architectures. This talk will highlight mechanisms and consequences of this obliquity-driven sculpting. First, I will show how obliquity tides may explain the mysterious overabundance of planets wide of mean-motion resonances in short-period, compact systems. Second, I will outline how similar influences might account for the remarkably rapid orbital inspiral of the highly inflated hot Jupiter, WASP-12b. In both of these problems, the requisite large planetary obliquities can be maintained 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 typical compact, close-in systems frequently experience this mechanism, and I will highlight additional features in the observed planet population that may be its signatures.