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Photograph of Ross Church

Ross Church

Senior lecturer

Photograph of Ross Church

Can planetary instability explain the Kepler dichotomy?

Author

  • Anders Johansen
  • Melvyn B Davies
  • Ross Church
  • Viktor Holmelin

Summary, in English

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, varying the internal inclination variation of the orbits. 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 5 degrees. Our analysis shows that the Kepler data contain a population of planets larger than four Earth radii in single-transit systems that cannot 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 by planet-planet collisions, and less frequently by ejections or collisions with the star, yielding transits in agreement with the large planets in the Kepler single-transit systems. The resulting population of massive double-planet systems nevertheless cannot 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. Planetary instability of systems of triple gas-giant planets can be behind part of the dichotomy between systems hosting one or more small planets and those hosting a single giant planet. The main part of the dichotomy, however, 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.

Department/s

  • Lund Observatory

Publishing year

2012

Language

English

Publication/Series

Astrophysical Journal

Volume

758

Issue

1

Document type

Journal article

Publisher

American Astronomical Society

Topic

  • Astronomy, Astrophysics and Cosmology

Keywords

  • planets and satellites: dynamical evolution and stability
  • planets and
  • satellites: formation
  • protoplanetary disks

Status

Published

ISBN/ISSN/Other

  • ISSN: 0004-637X