The curiously circular orbit of Kepler-16b

Abstract

The recent discovery of a number of circumbinary planets lends a new tool to astrophysicists seeking to understand how and where planet formation takes place. Of the increasingly numerous circumbinary systems, Kepler-16 is arguably the most dynamically interesting: it consists of a planet on an almost perfectly circular orbit (e = 0.0069) around a moderately eccentric binary (e = 0.16). We present high-resolution 3D smoothed-particle hydrodynamics simulations of a Kepler-16 analogue embedded in a circumbinary disc, and show that the planet's eccentricity is damped by its interaction with the protoplanetary disc. We use this to place a lower limit on the gas surface density in the real disc through which Kepler-16b migrated of Σ_min ~ 10 g cm^-2. This suggests that Kepler-16b, and other circumbinary planets, formed and migrated in relatively massive discs. We argue that secular evolution of circumbinary discs requires that these planets likely formed early on in the lifetime of the disc and migrated inwards before the disc lost a significant amount of its original mass.

7 pages, 6 figures. Accepted for publication in MNRAS. Movies of the simulations can be found at: http://www.astro.le.ac.uk/~acd23/K16.html

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• Evolution of circumbinary planets around eccentric binaries: The case of Kepler-34
• Spiral patterns in planetesimal circumbinary disks
• Assessing Circumbinary Habitable Zones using Latitudinal Energy Balance Modelling
• The Role of Disc Self-Gravity in Circumbinary Planet Systems: I. Disc Structure and Evolution
• On The Lack of Circumbinary Planets Orbiting Isolated Binary Stars
• Milankovitch Cycles of Terrestrial Planets in Binary Star Systems
• Coevolution of Binaries and Gaseous Discs
• Dusty circumbinary discs: inner cavity structures and stopping locations of migrating planets
• Global N-body simulations of circumbinary planet formation around Kepler-16 and -34 analogues I: Exploring the pebble accretion scenario
• The Role of Disc Self-Gravity in Circumbinary Planet Systems: II. Planet Evolution
• A self-consistent weak friction model for the tidal evolution of circumbinary planets
• Tidal evolution of circumbinary systems with arbitrary eccentricities: applications for Kepler systems