Milankovitch Cycles of Terrestrial Planets in Binary Star Systems

TL;DR

This study models the climate and orbital dynamics of planets in binary star systems, revealing Milankovitch-like cycles and climate oscillations driven by gravitational perturbations, with implications for planetary habitability.

Contribution

It introduces a coupled climate-orbit model to analyze gravito-climatic oscillations in binary star systems, a novel approach for understanding planetary climate variability.

Findings

Earth-like planets in Kepler-47 experience 1000-year Milankovitch cycles.

Alpha Centauri planets show 15,000-year eccentricity variations affecting climate.

Long-term climate cycles of 100,000 years are driven by phase drifts and planetary interactions.

Abstract

The habitability of planets in binary star systems depends not only on the radiation environment created by the two stars, but also on the perturbations to planetary orbits and rotation produced by the gravitational field of the binary and neighbouring planets. Habitable planets in binaries may therefore experience significant perturbations in orbit and spin. The direct effects of orbital resonances and secular evolution on the climate of binary planets remain largely unconsidered. We present latitudinal energy balance modelling of exoplanet climates with direct coupling to an N Body integrator and an obliquity evolution model. This allows us to simultaneously investigate the thermal and dynamical evolution of planets orbiting binary stars, and discover gravito-climatic oscillations on dynamical and secular timescales. We investigate the Kepler-47 and Alpha Centauri systems as archetypes of P and S type binary systems respectively. In the first case, Earthlike planets would experience rapid Milankovitch cycles (of order 1000 years) in eccentricity, obliquity and precession, inducing temperature oscillations of similar periods (modulated by other planets in the system). These secular temperature variations have amplitudes similar to those induced on the much shorter timescale of the binary period. In the Alpha Centauri system, the influence of the secondary produces eccentricity variations on 15,000 year timescales. This produces climate oscillations of similar strength to the variation on the orbital timescale of the binary. Phase drifts between eccentricity and obliquity oscillations creates further cycles that are of order 100,000 years in duration, which are further modulated by neighbouring planets.