Thursday, May 26, 2016

Tidal Decay and Disruption of hot gas Giants

Tidal Decay and Disruption of Short-Period Gaseous Exoplanets


Jackson et al


Many gaseous exoplanets in short-period orbits are on the verge or are in the process of tidal disruption. Moreover, orbital stability analysis shows tides can drive many hot Jupiters to spiral toward their host stars. Thus, the coupled processes of orbital evolution and tidal disruption likely shape the observed distribution of close-in exoplanets and may even be responsible for producing some of the short-period rocky planets. However, the exact outcome for a disrupting planet depends on its internal response to mass loss, and the accompanying orbital evolution can act to enhance or inhibit the disruption process. In this study, we apply the fully-featured and robust Modules for Experiments in Stellar Astrophysics (MESA) suite to model Roche-lobe overflow (RLO) of short-period gaseous planets. We show that, although the detailed evolution may depend on several properties of the planetary system, it is largely determined by the core mass of the disrupting gas giant. In particular, we find that the orbital expansion that accompanies RLO often stops and reverses at a specific maximum period that depends on the core mass. We suggest that RLO may often strand the remnant of a disrupted gas giant near this orbital period, which provides an observational prediction that can corroborate the hypothesis that short period gas giants undergo RLO. We conduct a preliminary comparison of this prediction to the observed population of small, short-period planets and find some planets in orbits that may be consistent with this picture. To the extent that we can establish some short-period planets are indeed the remnants of disrupted gas giants, that population can elucidate the properties of gas giant cores, the properties of which remain largely unconstrained.

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