Potential of Hot Jupiters Within Host Star Roche Limits

Planets on the Edge

Authors:

Valsecchi et al

Abstract:

Hot Jupiters formed through circularization of high-eccentricity orbits should be found at orbital separations a exceeding twice that of their Roche limit aR. Nevertheless, about a dozen giant planets have now been found well within this limit (aR less than a less than 2aR), with one coming as close as 1.2aR. In this Letter, we show that orbital decay (starting beyond 2aR) driven by tidal dissipation in the star can naturally explain these objects. For a few systems (WASP-4 and 19), this explanation requires the linear reduction in convective tidal dissipation proposed originally by Zahn (1966) and verified by recent numerical simulations (Penev et al. 2007), but rules out the quadratic prescription proposed by Goldreich and Nicholson (1977). Additionally, we find that WASP-19-type systems could potentially provide empirical support to the Zahn's (1966) prescription through high precision transit timing measurements of their orbital decay rate.