Is Gliese 581d habitable? Some constraints from radiative-convective climate modeling

TL;DR

This study uses climate modeling to evaluate if the exoplanet Gliese 581d could maintain liquid water, suggesting it might be habitable under certain atmospheric conditions, but further 3D simulations are needed for stability confirmation.

Contribution

The paper provides the first detailed climate modeling analysis of Gliese 581d's habitability potential considering various greenhouse gas scenarios.

Findings

Less than 10 bars of CO2 can keep surface temperatures above water's melting point.

Temperatures above melting point are possible with CO2 pressures over 40 bars.

Further 3D simulations are necessary to confirm atmospheric stability due to tidal effects.

Abstract

The recently discovered exoplanet Gl581d is extremely close to the outer edge of its system's habitable zone, which has led to much speculation on its possible climate. We have performed a range of simulations to assess whether, given simple combinations of chemically stable greenhouse gases, the planet could sustain liquid water on its surface. For best estimates of the surface gravity, surface albedo and cloud coverage, we find that less than 10 bars of CO2 is sufficient to maintain a global mean temperature above the melting point of water. Furthermore, even with the most conservative choices of these parameters, we calculate temperatures above the water melting point for CO2 partial pressures greater than about 40 bar. However, we note that as Gl581d is probably in a tidally resonant orbit, further simulations in 3D are required to test whether such atmospheric conditions are stable against the collapse of CO2 on the surface.