Laboratory Simulations of Haze Formation in the Atmospheres of super-Earths and mini-Neptunes: Particle Color and Size Distribution

TL;DR

This study conducts laboratory experiments to understand haze particle formation in super-Earth and mini-Neptune atmospheres, revealing how temperature and metallicity influence particle properties and impacting exoplanet climate and habitability assessments.

Contribution

It provides new experimental data on haze particle color, size, and optical properties under various planetary atmospheric conditions, aiding in exoplanet atmosphere modeling.

Findings

Particle color and size depend on atmospheric temperature and metallicity.

Haze particles' optical properties influence exoplanet climate and habitability.

Results inform future observational strategies with TESS, JWST, and WFIRST.

Abstract

Super-Earths and mini-Neptunes are the most abundant types of planets among the ~3500 confirmed exoplanets, and are expected to exhibit a wide variety of atmospheric compositions. Recent transmission spectra of super-Earths and mini-Neptunes have demonstrated the possibility that exoplanets have haze/cloud layers at high altitudes in their atmospheres. However, the compositions, size distributions, and optical properties of these particles in exoplanet atmospheres are poorly understood. Here, we present the results of experimental laboratory investigations of photochemical haze formation within a range of planetary atmospheric conditions, as well as observations of the color and size of produced haze particles. We find that atmospheric temperature and metallicity strongly affect particle color and size, thus altering the particles' optical properties (e.g., absorptivity, scattering, etc.); on a larger scale, this affects the atmospheric and surface temperature of the exoplanets, and their potential habitability. Our results provide constraints on haze formation and particle properties that can serve as critical inputs for exoplanet atmosphere modeling, and guide future observations of super-Earths and mini-Neptunes with the Transiting Exoplanet Survey Satellite (TESS), the James Webb Space Telescope (JWST), and the Wide-Field Infrared Survey Telescope (WFIRST).