Saving Doomed Planets: Mass Loss and Angular Momentum Return Boost Hot Jupiter Survival Rates

Abstract

The existence of giant extrasolar planets on short-period orbits ("hot Jupiters") challenges planet formation theories because such planets are difficult to form close to the star. High-eccentricity migration is a leading explanation, in which giant planets born at large separations are excited to near-unity eccentricities, enabling tidal dissipation at periastron to shrink and circularize their orbits. While observations of orbital misalignments and eccentric planets support this scenario, high-eccentricity migration models struggle to reproduce the observed hot Jupiter occurrence rate. Population synthesis studies often predict that many source "cold Jupiters" are destroyed by tidal disruption at high eccentricities. We revisit this question with improved treatments of mass loss and angular momentum return experienced by tidally perturbed planets. As a test case, we explore eccentricity excitations driven by wide stellar companions via the Eccentric Kozai-Lidov (EKL) mechanism. We show using an analytical framework that planets may avoid complete disruption and ultimately survive as stripped hot Jupiters. To capture detailed planetary mass loss over many orbits, we perform numerical studies that combine secular dynamical evolution with planetary structure evolution. Our new population synthesis studies show that hot Jupiter survival is enhanced by a factor of $\sim2-3$ relative to previous estimates, yielding occurrence rates ($\gtrsim 0.5\%$ around FGK stars) consistent with observations. Angular momentum return from mass accreted onto the star may also produce a pileup of hot Jupiters near three-day orbital periods. These results suggest that high-eccentricity migration, when accounting for tidal mass loss, may be a dominant channel for hot Jupiter formation.