Hot Super Earths: disrupted young jupiters?

Abstract

Recent {\em Kepler} observations revealed an unexpected abundance of "hot" Earth-size to Neptune-size planets in the inner $0.02-0.2$ AU from their parent stars. We propose that these smaller planets are the remnants of massive giant planets that migrated inward quicker than they could contract. We show that such disruptions naturally occur in the framework of the Tidal Downsizing hypothesis for planet formation. We find that the characteristic planet-star separation at which such "hot disruptions" occur is $R \approx 0.03-0.2$ AU. This result is independent of the planet's embryo mass but is dependent on the accretion rate in the disc. At high accretion rates, $\dot M \simgt 10^{-6}\msun$ yr$^{-1}$, the embryo is unable to contract quickly enough and is disrupted. At late times, when the accretion rate drops to $\dot M \simlt 10^{-8} \msun$ yr$^{-1}$, the embryos migrate sufficiently slow to not be disrupted. These "late arrivals" may explain the well known population of hot jupiters. If type I migration regime is inefficient, then our model predicts a pile-up of planets at $R\sim 0.1$ AU as the migration rate suddenly switches from the type II to type I in that region.