Spin dynamics of close-in planets exhibiting large transit timing variations

¹ Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
e-mail: jean-baptiste.delisle@unige.ch
² ASD, IMCCE, Observatoire de Paris – PSL Research University, UPMC Univ. Paris 6, CNRS, 77 Avenue Denfert-Rochereau, 75014 Paris, France
³ CIDMA, Departamento de Física, Universidade de Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal
⁴ Physikalisches Institut & Center for Space and Habitability, Universitaet Bern, 3012 Bern, Switzerland

Received: 9 March 2017
Accepted: 1 May 2017

Abstract

We study the spin evolution of close-in planets in compact multi-planetary systems. The rotation period of these planets is often assumed to be synchronous with the orbital period due to tidal dissipation. Here we show that planet-planet perturbations can drive the spin of these planets into non-synchronous or even chaotic states. In particular, we show that the transit timing variation (TTV) is a very good probe to study the spin dynamics, since both are dominated by the perturbations of the mean longitude of the planet. We apply our model to KOI-227 b and Kepler-88 b, which are both observed undergoing strong TTVs. We also perform numerical simulations of the spin evolution of these two planets. We show that for KOI-227 b non-synchronous rotation is possible, while for Kepler-88 b the rotation can be chaotic.