Habitability in 4-D: Predicting the Climates of Earth Analogs across Rotation and Orbital Configurations

TL;DR

This study uses climate modeling and statistical emulation to predict how different rotation and orbital parameters affect the habitability of Earth-like planets, revealing key factors influencing climate stability.

Contribution

It introduces a novel emulator approach to efficiently predict planetary habitability across a wide range of spin-orbit configurations, validated against detailed GCM simulations.

Findings

Rotation period is the primary driver of habitability for eccentricities up to 0.225.

Habitability significantly decreases for rotation periods longer than ~20 days.

Obliquity impacts habitability notably for planets with short rotation periods.

Abstract

Earth-like planets in the circumstellar habitable zone (HZ) may have dramatically different climate outcomes depending on their spin-orbit parameters, altering their habitability for life as we know it. We present a suite of 93 ROCKE-3D general circulation models (GCMs) for planets with the same surface conditions and average annual insolation as Earth, but with a wide range of rotation periods, obliquities, orbital eccentricities, and longitudes of periastra. Our habitability metric $f_\mathrm{HZ}$ is calculated based on the temperature and precipitation in each model across grid cells over land. Latin Hypercube Sampling (LHS) aids in sampling all 4 of the spin-orbit parameters with a computationally feasible number of GCM runs. Statistical emulation then allows us to model $f_\mathrm{HZ}$ as a smooth function with built-in estimates of statistical uncertainty. We fit our emulator to an initial set of 46 training runs, then test with an additional 46 runs at different spin-orbit values. Our emulator predicts the directly GCM-modeled habitability values for the test runs at the appropriate level of accuracy and precision. For orbital eccentricities up to 0.225, rotation period remains the primary driver of the fraction of land that remains above freezing and with precipitation above a threshold value. For rotation periods greater than $\sim 20$ days, habitability drops significantly (from $\sim 70$% to $\sim 20$%), driven primarily by cooler land temperatures. Obliquity is a significant secondary factor for rotation periods less than $\sim 20$ Earth days, with a factor of two impact on habitability that is maximized at intermediate obliquity.