Haze Production in the Atmospheres of super-Earths and mini-Neptunes: Insights from the Lab

TL;DR

This study presents laboratory simulations of haze formation in super-Earth and mini-Neptune atmospheres, revealing that haze presence depends on temperature and metallicity, with some atmospheres producing significant haze particles.

Contribution

First laboratory experiments simulating haze formation in exoplanet atmospheres across various temperatures and metallicities, providing insights into haze occurrence and production rates.

Findings

Haze particles form in all simulated atmospheres.

Haze production rates vary significantly with conditions.

Some atmospheres produce haze rates comparable to Titan.

Abstract

Numerous solar system atmospheres possess aerosols including the characteristic organic hazes of Titan and Pluto. Haze particles substantially impact atmospheric temperatures structures and may provide organic material to the surface of a world, thereby affecting its habitability. Observations of exoplanet atmospheres suggest the presence of aerosols, especially in cooler (<800 K), smaller (<0.3 times Jupiter's mass) exoplanets. It remains unclear if the aerosols muting the spectroscopic features of exoplanet atmospheres are condensate clouds or photochemical hazes, which is difficult to predict from theory alone. We present here the first laboratory haze simulation experiments for atmospheric compositions expected for super-Earths and mini-Neptunes. We explored temperatures from 300 to 600 K and a range of atmospheric metallicities (100x, 1000x, 10000x solar); all simulated atmospheres produced particles, and the cooler (300 and 400 K) 1000x solar metallicity ("H2O-dominated", CH4-rich) experiments exhibited haze production rates higher than our standard Titan simulation (~10 mg/hr versus 7.4 mg/hr for Titan). However the particle production rates varied greatly, with measured rates as low as 0.04 mg/hr (100x solar metallicity, 600 K). Here we show that we should expect some, but not all, super-Earth and mini-Neptune atmospheres to possess a thick photochemically generated haze.