Characterizing the Radiative-Convective Structure of Dense Rocky Planet Atmospheres

TL;DR

This study models dense rocky planet atmospheres to understand how shortwave absorption by gases like H2O and CO2 influences surface temperatures and convection, revealing significant cooling effects and the importance of high-temperature spectroscopy.

Contribution

It introduces a one-dimensional radiative-convective model to analyze the impact of shortwave absorption on dense planetary atmospheres, highlighting the cooling effects of CO2 and H2O and the limited warming by minor gases.

Findings

H2O and CO2 absorption inhibits near-surface convection.

Pure CO2 atmospheres are cooler than H2O atmospheres by about 1000 K.

Mixed CO2-H2O atmospheres maintain high surface temperatures even at high insolation.

Abstract

We use a one-dimensional line-by-line radiative-convective model to simulate hot, dense terrestrial-planet atmospheres. We find that strong shortwave absorption by H2O and CO2 inhibits near-surface convection, reducing surface temperatures by up to approximately 2000 K compared to fully convective predictions. Pure CO2 atmospheres are typically 1000 K cooler than pure H2O atmospheres, with only a few percent of H2O needed to elevate surface temperatures by hundreds of kelvin for a fixed incident stellar radiation. We also show that minor greenhouse gases such as SO2 and NH3 have a limited warming effect when H2O is abundant. Even at insolation values as high as 12,500 W/m2 (about 37 times Earth's current solar flux), planets with mixed CO2-H2O envelopes have surface temperatures in the 1200 to 2000 K range, limiting surface melting. Our results highlight the critical role of shortwave heating on magma ocean planets and the need for improved high-temperature spectroscopy beyond 20,000 cm-1.