The Most Common Habitable Planets III -- Modeling Temperature Forcing and Surface Conditions on Rocky Exoplanets and Exomoons

TL;DR

This paper models temperature forcing and surface conditions on rocky exoplanets and exomoons, exploring how orbital eccentricity and atmospheric properties influence habitability and surface temperature variations.

Contribution

It extends a previous model to real and hypothetical exoplanets and exomoons, analyzing temperature variations due to radiative forcing across different orbital and planetary parameters.

Findings

Temperature variations up to ~80 K for airless planets with e ~0.3.

Exomoons can experience temperature swings up to ~200 K at high eccentricities.

Potential detectability of these effects with future telescopes.

Abstract

Small rocky planets, as well as larger planets that suffered extensive volatile loss, tend to be drier and have thinner atmospheres as compared to Earth. Such planets probably outnumber worlds better endowed with volatiles, being the most common habitable planets. For the subgroup of fast rotators following eccentric orbits, atmospheres suffer radiative forcing and their heat capacity provides a method for gauging atmospheric thickness and surface conditions. We further explore the model presented in a previous paper and apply it to real and hypothetical exoplanets in the habitable zone of various classes of stars, simulating atmospheric and orbital characteristics. For planetary eccentricities e ~0.3, the forcing-induced hypothetical temperature variation would reach ~80 K for airless planets and ~10 K for planets with substantial atmospheres. For Kepler-186 f and Kepler-442 b, assuming e ~0.1, temperature variations can reach ~24 K. We also consider habitable exomoons in circular orbits around gas giants within the habitable zone, which suffer radiative forcing due to their epicyclic motion. We study several combinations of parameters for the characterization of planets (mass, eccentricity and semi-major axis) and exomoons (mass, orbital radius, albedo and atmospheric characteristics) for different stellar types. For e ~0.3, exomoon temperature varies up to ~90 K, while for ~0.6 variations can reach ~200 K. Such exomoons may plausibly retain their volatiles by continued volcanic activity fueled by tidal dissipation. Although currently undetectable, such effects might be within reach of future Extremely Large Telescope-class telescopes and space missions with mid-infrared and coronagraphic capabilities.