The Influence of Hydrogen Sulfide on the Optical Properties of Planetary Organic Hazes: Implications for Exoplanet Climate Modeling

Abstract

Planetary organic hazes can play a significant role in influencing a planet’s radiative balance and climate, with their impact determined by the optical properties of the haze. The optical properties, in turn, are partly influenced by particle composition. Our previous work, Reed et al., demonstrated that trace amounts of hydrogen sulfide (H _2 S) in haze chemistry can substantially affect the haze’s composition by generating organosulfur compounds and increasing the amount of organic haze produced. However, no study has measured the optical properties of an H _2 S-influenced organic haze. Here we present results from laboratory experiments measuring the real (scattering, n ) and imaginary (absorbing, k ) refractive indices of haze analogs produced from photochemistry of gas mixtures composed of 0.1% CH _4 and variable H _2 S (0–10 ppm _v ) in N _2 . The optical properties of the aerosol produced were measured in real-time using coupled photoacoustic and cavity ring-down spectroscopy with 405 and 532 nm wavelengths of light. Our findings show that the total extinction of light (scattering plus absorption) by the aerosol increases as a function of H _2 S mixing ratio. We provide our best-fit equations for predicting n and k at 405 and 532 nm as a function of the sulfur to carbon molar ratio (S:C) of the precursor gas mixture. Further, we demonstrate how these changes in optical properties could alter the transmittance of 405 and 532 nm light through a haze layer. These results have potential implications for modeling the climate, habitability, and spectra for exoplanets exhibiting organic haze.

Keywords

• Exoplanet atmospheres
• Optical constants (Dust)
• Exoplanet atmospheric composition
• Planetary climates
• Planetary atmospheres