How not to build Tatooine: the difficulty of in situ formation of circumbinary planets Kepler 16b, Kepler 34b and Kepler 35b

摘要

We study planetesimal evolution in circumbinary disks, focusing on the threesystems Kepler 16, 34 and 35 where planets have been discovered recently. Weshow that for circumbinary planetesimals, in addition to secular forcing,eccentricities evolve on a dynamical timescale, which leads to orbitalcrossings even in the presence of gas drag. This makes the current locations ofthe circumbinary Kepler planets hostile to planetesimal accretion. We thenpresent results from simulations including planetesimal formation and dustaccretion, and show that even in the most favourable case of 100% efficientdust accretion, in situ growth starting from planetesimals smaller than ~10 kmis difficult for Kepler 16b, Kepler 34b and Kepler 35b. These planets werelikely assembled further out in the disk, and migrated inward to their currentlocation.