Dynamical rearrangement of super-Earths during disk dispersal

II. Assessment of the magnetospheric rebound model for planet formation scenarios

Anton Pannekoek Institute (API), University of Amsterdam, Science Park 904, 1090GE Amsterdam, The Netherlands
e-mail: b.liu@uva.nl; c.w.ormel@uva.nl

Received: 28 March 2017
Accepted: 22 July 2017

Abstract

Context. The Kepler mission has provided a large sample to statistically analyze the orbital properties of the super-Earth planet population. We hypothesize that these planets formed early and consider the problem of matching planet formation theory to the current orbital configurations. Two scenarios – disk migration and in-situ formation – have been proposed to explain the origin of these planets. In the migration scenario, planets migrate inward to the inner disk due to planet-disk interaction, whereas in the in-situ scenario planets assemble locally. Therefore, planets formed by migration are expected to end up in resonances, whereas those formed in-situ are expected to stay in short period ratios and in non-resonant orbits. Both predictions are at odds with observations.

Aims. We investigate whether a preferred formation scenario can be identified through a comparison between the magnetospheric rebound model and the Kepler data.

Methods. We conduct N-body simulations of two-planet systems during the disk dispersal phase. Several distributions of model parameters are considered and we make a statistical comparison between the simulations and the Kepler observations.

Results. Comparing the migration and the in-situ scenarios, we find that magnetospheric rebound tends to erase the difference in the orbital configuration that was initially presented. After disk dispersal, not all planets are in resonance in the migration scenario, whereas planets do not remain in compact configurations in the in-situ scenario. In both scenarios, the orbits of planets increase with the cavity expansion, and their period ratios have a wider distribution.

Conclusions. From a statistical perspective, the magnetospheric rebound model reproduces several observed properties of Kepler planets, such as the fact that a significant number of planets are not in resonances and planet pairs can end up at large period ratios. The disparity in orbital configuration between the two formation scenarios is substantially reduced after disk dispersal.