Planet–planet scattering alone cannot explain the free-floating planet population

Authors

  • Dimitri Veras,

    Corresponding author
    1. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA
      E-mail: veras@ast.cam.ac.uk (DM); rayray.sean@gmail.com (SNR)
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  • Sean N. Raymond

    Corresponding author
    1. CNRS, UMR 5804, Laboratoire d’Astrophysique de Bordeaux, 2 rue de l’Observatoire, BP 89, F-33271 Floirac Cedex, France
    2. Observatoire Aquitain des Sciences de l’Univers, Université de Bordeaux, 2 rue de l’Observatoire, BP 89, F-33271 Floirac Cedex, France
      E-mail: veras@ast.cam.ac.uk (DM); rayray.sean@gmail.com (SNR)
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E-mail: veras@ast.cam.ac.uk (DM); rayray.sean@gmail.com (SNR)

ABSTRACT

Recent gravitational microlensing observations predict a vast population of free-floating giant planets that outnumbers main-sequence stars almost twofold. A frequently invoked mechanism for generating this population is a dynamical instability that incites planet–planet scattering and the ejection of one or more planets in isolated main-sequence planetary systems. Here, we demonstrate that this process alone probably cannot represent the sole source of these Galactic wanderers. By using straightforward quantitative arguments and N-body simulations, we argue that the observed number of exoplanets exceeds the plausible number of ejected planets per system from scattering. Thus, other potential sources of free floaters, such as planetary stripping in stellar clusters and post-main-sequence ejection, must be considered.

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