# Spin dynamics of close-in planets exhibiting large TTVs

## TL;DR

This paper investigates how gravitational interactions in multi-planet systems can lead to non-synchronous and chaotic spin states in close-in planets, using TTVs as a diagnostic tool.

## Contribution

It demonstrates that planet-planet perturbations can significantly alter the spin states of close-in planets, challenging the common assumption of synchronous rotation.

## Key findings

- KOI-227b can have non-synchronous rotation.
- Kepler-88b's rotation can become chaotic.
- TTVs effectively probe spin dynamics.

## 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-227b and Kepler-88b, 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-227b non-synchronous rotation is possible, while for Kepler-88b the rotation can be chaotic.