Anders Johansen, Melvyn B. Davies, Ross P. Church, Viktor Holmelin
The planet candidates discovered by the Kepler mission provide a rich sample to constrain the architectures and relative inclinations of planetary systems within approximately 0.5 AU of their host stars. We use the triple-transit systems from the Kepler 16-months data as templates for physical triple-planet systems and perform synthetic transit observations. We find that all the Kepler triple-transit and double-transit systems can be produced from the triple-planet templates, given a low mutual inclination of around five degrees. Our analysis shows that the Kepler data contains a population of planets larger than four Earth radii in single-transit systems that can not arise from the triple-planet templates. We explore the hypothesis that high-mass counterparts of the triple-transit systems underwent dynamical instability to produce a population of massive double-planet systems of moderately high mutual inclination. We perform N-body simulations of mass-boosted triple-planet systems and observe how the systems heat up and lose planets, most frequently by planet-planet collisions, yielding transits in agreement with the large planets in the Kepler single-transit systems. The resulting population of massive double-planet systems can nevertheless not explain the additional excess of low-mass planets among the observed single-transit systems and the lack of gas-giant planets in double-transit and triple-transit systems. While planetary instability of systems of triple gas-giant planets can be behind part of the dichotomy in the Kepler data between systems showing one transit and systems showing two or more transits, the main part of the dichotomy is more likely to have arisen already during planet formation when the formation, migration or scattering of a massive planet, triggered above a threshold metallicity, suppressed the formation of other planets in sub-AU orbits.
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http://arxiv.org/abs/1206.6898
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