A flat inner disc model as an alternative to the Kepler dichotomy in the Q1-Q16 planet population

Abstract

We use simulated planetary systems to model the planet multiplicity of Kepler stars. Previous studies have underproduced single planet systems and invoked the so-called Kepler dichotomy, where the planet forming ability of a Kepler star is dichotomous, producing either few or many transiting planets. In this paper, we show that the Kepler dichotomy is only required when the inner part of planetary discs are just assumed to be flared. When the inner part of planetary discs are flat, we reproduce the observed planet multiplicity of Kepler stars without the need to invoke a dichotomy. We find that independent of the disc model assumed, the mean number of planets per star μ ≈ 2 for orbital periods between 3 and 200 d, and for planetary radii between 1 and 5 Earth radii. This contrasts with the Solar system where no planets occupy the same parameter space.