The Phase-curve Signature of Condensible Water-rich Atmospheres on Slowly Rotating Tidally Locked Exoplanets

TL;DR

This study uses a 3D climate model to explore the thermal emission patterns of condensible water-rich atmospheres on slowly rotating, tidally locked exoplanets, revealing how emission contrasts inform atmospheric composition and pressure.

Contribution

It introduces a novel analysis of thermal emission contrasts in thin, water-rich atmospheres, linking emission patterns to atmospheric properties on tidally locked exoplanets.

Findings

Thermal emission reversal between day and night hemispheres observed.

Contrast in thermal emission indicates water vapor ratio and atmospheric pressure.

Thin, temperate atmospheres show similar dynamics to thick, runaway greenhouse atmospheres.

Abstract

We use an idealized three-dimensional general circulation model to study condensible-rich atmospheres with an ineffective cold trap on slowly rotating tidally locked terrestrial planets. In particular, we show the climate dynamics in a thin and temperate atmosphere with condensible water vapor. The similarities between our thin and temperate atmosphere and the warm and thick atmosphere approaching the water vapor runaway greenhouse in previous works are discussed, including the reversal of the thermal emission between the day and night hemispheres. Different from the transit spectroscopy of water vapor that depends on the absolute amount of atmospheric water vapor, the contrast between the dayside and nightside thermal emission provides information regarding the relative ratio of water vapor to the background atmosphere as well as the atmospheric pressure near the substellar tropopause and the emission level on the nightside on potentially habitable worlds.