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The Dynamical Origins of Kepler-1656b’s Extreme Eccentricity

Published onAug 03, 2020
The Dynamical Origins of Kepler-1656b’s Extreme Eccentricity

Highly eccentric orbits are one of the major surprises of exoplanets relative to the Solar System, and are typically indicative of a rich dynamical history. One system of particular interest is Kepler-1656, which hosts a single known planet on a close-in, highly eccentric (e = 0.84) orbit. This orbital configuration places Kepler-1656b on the extreme upper envelope of the e-a diagram and is not a typical outcome of planet formation. Instead, planets formed in a near-circular orbit can be driven to much higher eccentricities via pathways such as planet-planet scattering, perturbation from a stellar flyby, or Kozai evolution induced by an outer stellar or planetary companion in the system. To investigate the possibility of these scenarios, we use GAIA to place observational constraints on the properties of a potential companion or flyby perturber. We then examine the secular evolution of Kepler-1656b in the presence of a third, outer planet using dynamical modeling to assess the likelihood of a Kozai-driven eccentricity. Such methods can be applied to planets in similarly eccentric orbits to unveil potentially tumultuous histories in a variety of exoplanet systems.

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