How to build Tatooine: reducing secular excitation in Kepler circumbinary planet formation

Abstract

Circumbinary planetary systems recently discovered by Kepler represent an important testbed for planet formation theories. Planetesimal growth in disks around binaries has been expected to be inhibited interior to ~10 AU by secular excitation of high relative velocities between planetesimals, leading to their collisional destruction (rather than agglomeration). Here we show that gravity of the gaseous circumbinary disk in which planets form drives fast precession of both the planetesimal and binary orbits, resulting in strong suppression of planetesimal eccentricities beyond 2-3 AU and making possible growth of 1-100 km objects in this region. The precise location of the boundary of accretion-friendly region depends on the size of the inner disk cavity cleared by the binary torques and on the disk mass (even 0.01 M_Sun disk strongly suppresses planetesimal excitation), among other things. Precession of the orbit of the central binary, enhanced by the mass concentration naturally present at the inner edge of a circumbinary disk, plays key role in this suppression, which is a feature specific to the circumbinary planet formation.

6 pages, 2 figures, submitted to ApJL

References in corpus (7)

• The Transiting Circumbinary Planets Kepler-34 and Kepler-35
• Kepler-47: A Transiting Circumbinary Multi-Planet System
• The Neptune-Sized Circumbinary Planet Kepler-38b
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• Relative velocities among accreting planetesimals in binary systems: the circumbinary case
• The formation of planets in circumbinary disks
• Planet Formation in Circumbinary Configurations: Turbulence Inhibits Planetesimal Accretion

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