Global N-body simulations of circumbinary planet formation around Kepler-16 and -34 analogues I: Exploring the pebble accretion scenario

Abstract

Numerous circumbinary planets have been discovered in surveys of transiting planets. Often, these planets are found to orbit near to the zone of dynamical instability, close to the central binary. The existence of these planets has been explained by hydrodynamical simulations that show that migrating circumbinary planets, embedded in circumbinary discs, halt at the central cavity that is formed by the central binary. Transit surveys are naturally most sensitive to finding circumbinary planets with the shortest orbital periods. The future promise of detecting longer period systems using radial-velocity searches, combined with the anticipated detection of numerous circumbinary planets by ESA’s PLATO mission, points to the need to model and understand the formation and evolution of circumbinary planets in a more general sense than has been considered before. With this goal in mind, we present a newly developed global model of circumbinary planet formation that is based on the mercury6 symplectic N-body integrator, combined with a model for the circumbinary disc and prescriptions for a range of processes involved in planet formation such as pebble accretion, gas envelope accretion and migration. Our results show that under reasonable assumptions, the pebble accretion scenario can produce circumbinary systems that are similar to those observed, and in particular is able to produce planets akin to Kepler-16b and Kepler-34b. Comparing our results to other systems, we find that our models also adequately reproduce such systems, including multi-planet systems. Resonances between neighbouring planets are frequently obtained, whilst ejections of planets by the central binary acts as an effective source of free floating planets.

Photo-dynamical Analysis of Circumbinary Multi-planet System TOI-1338: A Fully Coplanar Configuration with a Puffy Planet

“…In Figure 10 Lee & Chiang (2016) suggest that planets with such low density might have migrated from a distant region where the disk is cool and has low opacity, enabling efficient cooling of the accretion and forming a massive envelope even with a low-mass core. This hypothesis aligns with the general picture that most observed CBPs may have undergone migration during their formation process (e.g., Pierens & Nelson 2013;Coleman et al 2023aColeman et al , 2023b, due to the local low growth rate of planetary cores near the stability limit, which hinders the in situ formation of CBPs (Pierens et al 2020(Pierens et al , 2021.…”

Free-floating Planet Mass Function from MOA-II 9 yr Survey toward the Galactic Bulge

“…Planets can be ejected from their hosts by dynamical interactions with other (mostly giant) planets (Rasio & Ford 1996;Weidenschilling & Marzari 1996;Lin & Ida 1997), by stellar flybys (Malmberg et al 2011), or by the post-MS evolution of their hosts (Adams et al 2013). Coleman et al (2023) simulated the circumbinary planetary systems for Kepler-16 and Kepler-34 and found that such systems may eject 6.3 and 9.3 planets on average, respectively, and most of these have masses smaller than Neptune. However, there are very few or almost no studies on the prediction for the number of the ejection of the Earth-to-Neptune-mass planet population because the abundance of such planets in less tightly bound wide orbits is not well known.…”

The PLATO Mission

“…Pierens et al, 2021). Development of population synthesis models of these types of systems (Coleman et al, 2023) will allow comparison with PLATO data, constraining theories of planet formation in diverse environments.…”