Clement Baruteau, John C. B. Papaloizou
The Kepler mission is dramatically increasing the number of planets known in multi-planetary systems. Some pairs of close adjacent planets have orbital period ratios close to resonant values, with a tendency to be larger than required for exact first-order mean-motion resonances. This intriguing feature has been shown to be a natural outcome of energy dissipation in resonant planetary pairs with conserved angular momentum, and tidal circularization due to star-planet interactions has been highlighted as a possible mechanism for such energy dissipation. However, many multi-planetary systems have orbital periods larger than ten days, for which tidal circularization is unlikely to provide efficient energy dissipation. Gravitational interactions between partial gap-opening planets and their parent protoplanetary disk may instead provide efficient dissipation. We show that disk-planet interactions can lead to resonant planet pairs with period ratios in significant excess to that of first-order resonant period ratios. It could help account for the diversity of period ratios in Kepler's planet pairs comprising super-Earth planets with orbital periods greater than about ten days. Fast disk-driven migration of sub-jovian planets may alternatively form planet pairs evolving in a common gap, where the planets' convergent migration may stall with a variety of period ratios. This mechanism is found to reproduce the period ratio of Kepler-46b/c.
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http://arxiv.org/abs/1301.0779
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