Tidal Sculpting of Short-Period Exoplanets

Sarah C. Millholland (Princeton University)

March 08, 2021

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Abstract: Multiple-planet systems composed of close-in super-Earth/sub-Neptune-sized planets are ubiquitous, representing the dominant outcome of planet formation. This population exhibits predictable hallmarks of architectural regularity and uniformity, such as low eccentricities and inclinations, similar orbital spacings, and intra-system correlations in planetary masses and radii. On top of this first-order structure, however, these systems also exhibit surprising anomalies that require explanation. Examples include (1) ultra-short period planets, whose extremely-irradiated orbits have been separated off from the rest of their systems; (2) planets piled up wide of mean-motion resonances; and (3) a subset of Neptune-sized planets that show signs of radius inflation. In this talk, I will propose that tidal dynamics can account for these specific anomalies and more. Specifically, I will discuss the critical role of enhanced tidal dissipation due to non-zero planetary axial tilts (obliquities), which arise by way of prevalent dynamical resonances. I will highlight strategies for testing these tidal theories and observing obliquities directly in the future.