Impact of photochemical hazes and gases on exoplanet atmospheric thermal structure

TL;DR

This study examines how photochemical hazes and disequilibrium gases influence the thermal structure of hot-Jupiter atmospheres, revealing their significant effects on temperature profiles and observational signatures.

Contribution

It introduces a detailed 1-D radiative-convective model to quantify the impact of photochemical hazes and gases on exoplanet atmospheric thermal structures, highlighting their importance in interpreting observations.

Findings

Photochemical hazes cause upper atmosphere heating and lower atmosphere cooling.

Sulphur species contribute to local heating near 1 mbar.

Photochemical gases affect temperature near 1 μbar and influence transit spectra.

Abstract

We investigate the impact of photochemical hazes and disequilibrium gases on the thermal structure of hot-Jupiters, using a detailed 1-D radiative-convective model. We find that the inclusion of photochemical hazes results in major heating of the upper and cooling of the lower atmosphere. Sulphur containing species, such as SH, S$_2$ and S$_3$ provide significant opacity in the middle atmosphere and lead to local heating near 1 mbar, while OH, CH, NH, and CN radicals produced by the photochemistry affect the thermal structure near 1 $\mu$bar. Furthermore we show that the modifications on the thermal structure from photochemical gases and hazes can have important ramifications for the interpretation of transit observations. Specifically, our study for the hazy HD 189733 b shows that the hotter upper atmosphere resulting from the inclusion of photochemical haze opacity imposes an expansion of the atmosphere, thus a steeper transit signature in the UV-Visible part of the spectrum. In addition, the temperature changes in the photosphere also affect the secondary eclipse spectrum. For HD 209458 b we find that a small haze opacity could be present in this atmosphere, at pressures below 1 mbar, which could be a result of both photochemical hazes and condensates. Our results motivate the inclusion of radiative feedback from photochemical hazes in general circulation models for a proper evaluation of atmospheric dynamics.