# Identifying Atmospheres on Rocky Exoplanets Through Inferred High Albedo

## TL;DR

This paper proposes a new method to detect atmospheres on rocky exoplanets around M/K dwarfs by inferring high albedo from thermal emission during secondary eclipse, indicating the presence of bright clouds.

## Contribution

It introduces a novel observational technique using thermal emission to identify high-albedo clouds as atmospheric indicators on rocky exoplanets.

## Key findings

- High albedo can signal an atmosphere with bright clouds.
- Cloud optical depths greater than 0.5-7 produce distinguishable high albedos.
- Method is effective for atmospheres with pressures below 1 bar.

## Abstract

The upcoming launch of the James Webb Space Telescope (JWST) means that we will soon have the capability to characterize the atmospheres of rocky exoplanets. However, it is still unknown whether such planets orbiting close to M dwarf stars can retain their atmospheres, or whether high-energy irradiation from the star will strip the gaseous envelopes from these objects. We present a new method to detect an atmosphere on a synchronously rotating rocky exoplanet around a K/M dwarf, by using thermal emission during secondary eclipse to infer a high dayside albedo that could only be explained by bright clouds. Based on calculations for plausible surface conditions, we conclude that a high albedo could be unambiguously interpreted as a signal of an atmosphere for planets with substellar temperatures of $T_{sub}=$ 410-1250 K. This range corresponds to equilibrium temperatures of $T_{eq}=$ 300-880 K. We compare the inferred albedos of eight possible planet surface compositions to cloud albedo calculations. We determine that a layer of clouds with optical depths greater than $\tau=0.5$-$7$, would have high enough albedos to be distinguishable from a bare rock surface. This method of detecting an atmosphere on a rocky planet is complementary to existing methods for detecting atmospheres, because it provides a way to detect atmospheres with pressures below 1 bar (e.g. Mars), which are too tenuous to transport significant heat but thick enough to host high-albedo clouds.