Exploring Tidal Obliquity Variations with SMERCURY-T

Abstract

We introduce our new code, SMERCURY-T, which is based on existing codes SMERCURY and Mercury-T. The result is a mixed-variable symplectic N-body integrator that can compute the orbital and spin evolution of a planet within a multiplanet system under the influence of tidal spin torques from its star. We validate our implementation by comparing our experimental results to that of a secular model. As we demonstrate in a series of experiments, SMERCURY-T allows for the study of secular spin–orbit resonance crossings and captures for planets within complex multiplanet systems. These processes can drive a planet’s spin state to evolve along vastly different pathways on its road toward tidal equilibrium, as tidal spin torques dampen the planet’s spin rate and evolve its obliquity. Additionally, we show the results of a scenario that exemplifies the crossing of a chaotic region that exists as the overlap of two spin–orbit resonances. The test planet experiences violent and chaotic swings in its obliquity until its eventual escape from resonance as it tidally evolves. All of these processes are and have been important over the obliquity evolution of many bodies within the solar system and beyond and have implications for planetary climate and habitability. SMERCURY-T is a powerful and versatile tool that allows for further study of these phenomena.

Self-consistent Spin, Tidal, and Dynamical Equations of Motion in the REBOUNDx Framework

“…They used this code to draw insights regarding the habitability of the Kepler-62 system (Borucki et al 2013) and showed the two planets in the system's habitable zone are likely to differ greatly in both obliquity and spin rate, with natural consequences for their habitability. Kreyche et al (2021) expanded on this framework with SMERCURY-T, providing a framework that can selfconsistently track the orbit and spin evolution of bodies in a multiplanet system under tidal influences from all bodies. Chen et al (2021) presented their independent consistent symplectic integrator package as well, GRIT.…”