# Photochemical hazes in sub-Neptunian atmospheres with focus on GJ 1214 b

## TL;DR

This study investigates photochemical haze formation in super-Earth and mini-Neptune atmospheres, especially GJ 1214b, across a range of metallicities, revealing how haze properties influence observable spectra and atmospheric characteristics.

## Contribution

It provides a comprehensive analysis of haze formation at various metallicities, including the effects of aggregate growth, and compares theoretical results with laboratory data, advancing understanding of exoplanet atmospheres.

## Key findings

- Higher metallicity leads to smaller haze particles.
- Haze opacity at high metallicity can obscure water features in spectra.
- Simulated spectra at extreme metallicity match observed transit depths at certain wavelengths.

## Abstract

We study the properties of photochemical hazes in super-Earths/mini-Neptunes atmospheres with particular focus on GJ1214b. We evaluate photochemical haze properties at different metallicities between solar and 10000$\times$solar. Within the four orders of magnitude change in metallicity, we find that the haze precursor mass fluxes change only by a factor of $\sim$3. This small diversity occurs with a non-monotonic manner among the different metallicity cases, reflecting the interaction of the main atmospheric gases with the radiation field. Comparison with relative haze yields at different metallicities from laboratory experiments reveals a qualitative similarity with our theoretical calculations and highlights the contributions of different gas precursors. Our haze simulations demonstrate that higher metallicity results into smaller average particle sizes. Metallicities at and above 100$\times$solar with haze formation yields of $\sim$10$\%$ provide enough haze opacity to satisfy transit observation at visible wavelengths and obscure sufficiently the H$_2$O molecular absorption features between 1.1 $\mu$m and 1.7 $\mu$m. However, only the highest metallicity case considered (10000$\times$solar) brings the simulated spectra into closer agreement with transit depths at 3.6 $\mu$m and 4.5 $\mu$m indicating a high contribution of CO/CO$_2$ in GJ1214b's atmosphere. We also evaluate the impact of aggregate growth in our simulations, in contrast to spherical growth, and find that the two growth modes provide similar transit signatures (for D$_f$=2), but with different particle size distributions. Finally, we conclude that the simulated haze particles should have major implications for the atmospheric thermal structure and for the properties of condensation clouds.