Exo-Milankovitch Cycles II: Climates of G-dwarf Planets in Dynamically Hot Systems

TL;DR

This study models the climate of Earth-like planets orbiting G dwarf stars, revealing that large orbital and obliquity variations can cause extreme ice ages and threaten habitability through snowball states, emphasizing the role of orbital dynamics.

Contribution

It introduces a combined climate and orbital dynamics model showing how exo-Milankovitch cycles impact habitability, with novel insights into ice edge instability driven by obliquity.

Findings

Ice caps strongly couple to orbital forcing, causing extreme ice ages.

Obliquity is the primary driver of ice edge instability.

Machine learning enhances climate model analysis.

Abstract

Using an energy balance model with ice sheets, we examine the climate response of an Earth-like planet orbiting a G dwarf star and experiencing large orbital and obliquity variations. We find that ice caps couple strongly to the orbital forcing, leading to extreme ice ages. In contrast with previous studies, we find that such exo-Milankovitch cycles tend to impair habitability by inducing snowball states within the habitable zone. The large amplitude changes in obliquity and eccentricity cause the ice edge, the lowest latitude extent of the ice caps, to become unstable and grow to the equator. We apply an analytical theory of the ice edge latitude to show that obliquity is the primary driver of the instability. The thermal inertia of the ice sheets and the spectral energy distribution of the G dwarf star increase the sensitivity of the model to triggering runaway glaciation. Finally, we apply a machine learning algorithm to demonstrate how this technique can be used to extend the power of climate models. This work illustrates the importance of orbital evolution for habitability in dynamically rich planetary systems. We emphasize that as potentially habitable planets are discovered around G dwarfs, we need to consider orbital dynamics.