Sulfur Hazes in Giant Exoplanet Atmospheres: Impacts on Reflected Light Spectra

Abstract

Recent work has shown that sulfur hazes may arise in the atmospheres of some giant exoplanets due to the photolysis of H${}_2$S. We investigate the impact such a haze would have on an exoplanet's geometric albedo spectrum and how it may affect the direct imaging results of WFIRST, a planned NASA space telescope. For temperate (250 K $<$ T${}_{\mathrm{eq}}$ $<$ 700 K) Jupiter--mass planets, photochemical destruction of H${}_2$S results in the production of $\sim$1 ppmv of \seight between 100 and 0.1 mbar, which, if cool enough, will condense to form a haze. Nominal haze masses are found to drastically alter a planet's geometric albedo spectrum: whereas a clear atmosphere is dark at wavelengths between 0.5 and 1 $\mu$m due to molecular absorption, the addition of a sulfur haze boosts the albedo there to $\sim$0.7 due to scattering. Strong absorption by the haze shortward of 0.4 $\mu$m results in albedos $<$0.1, in contrast to the high albedos produced by Rayleigh scattering in a clear atmosphere. As a result, the color of the planet shifts from blue to orange. The existence of a sulfur haze masks the molecular signatures of methane and water, thereby complicating the characterization of atmospheric composition. Detection of such a haze by WFIRST is possible, though discriminating between a sulfur haze and any other highly reflective, high altitude scatterer will require observations shortward of 0.4 $\mu$m, which is currently beyond WFIRST's design.

16 pages, 8 figures, 1 table, accepted for publication in AJ

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• Sulfur-driven Haze Formation in Warm CO2-rich Exoplanet Atmospheres
• Photochemical hazes in sub-Neptunian atmospheres with focus on GJ 1214 b
• Chemistry of Temperate Super-Earth and Mini-Neptune Atmospheric Hazes from Laboratory Experiments
• Detectable molecular features above hydrocarbon haze via transmission spectroscopy with JWST: Case studies of GJ 1214b-, GJ 436b-, HD 97658b-, and Kepler-51b-like planets
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• Reflected Light Phase Curves in the TESS Era
• How does the shape of the stellar spectrum affect the Raman scattering features in the albedo of exoplanets?