Probing Alien Sulfur Cycles: Their Effect on Climate and Implications for Observations

Sulfur is one of the most abundant elements in the cosmos and is readily outgassed as a volatile into planetary atmospheres. The conversion of sulfur-based gases to aerosol particles allows sulfur to significantly impact planetary climate via albedo changes and further can make it implicitly observable in exoplanet atmospheres because of the effects of sulfur-based hazes or clouds on atmospheric spectra. We explore the backbone of the sulfur cycle by coupling the evolution of SO2 gas, H2SO4 gas, H2SO4-H2O aerosols, and planetary surface composition. Sulfur is outgassed as SO2 and allowed to react with water vapor to form H2SO4 gas and aerosols. The sulfur aerosols and gasses continue to evolve via microphysics and chemical reactions until they are removed from the atmosphere by sedimentation, rainout, thermal decomposition, or surface reactions.

We probe the possible realizations of the sulfur cycle by exploring the parameter space of realistic surface pressures, surface temperatures, stellar insolations, local gravitational accelerations, outgassing rates, and atmospheric water concentrations with our simplified model. Our results characterize the various sulfur cycles by the average aerosol lifetime, the presence of a global cloud or haze layer, and the total radiative forcing. These metrics allow us to explore the range of effects of the sulfur cycle on climate in different planetary conditions and to begin the interpretation of potential observables to constrain:  surface temperature and pressure, water concentration, and plausible outgassing regimes.

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