. Gas-phase Organic Chemistry in Exoplanet Atmospheres and Implications for Haze Formation

Abstract
Atmospheric organic chemistry can lead to climate-altering organic haze and potentially form prebiotic molecules, making hazy planetary bodies of astrobiological interest. Despite extensive investigation into the composition of organic haze in laboratory simulations, there is a lack of understanding in the gas-phase composition and how this evolves temporally in simulation experiments. These measurements are necessary to inform models of planetary atmosphere. Here, we use an ethanol Chemical Ionization Mass Spectrometer (CIMS) to measure the chemical composition and temporal change of gas-phase products during the formation of haze analogs in Titan-like atmospheres. With Hierarchical Clustering Analysis (HCA), the evolution of gas-phase products was found to go from only organic species to organic nitrogen species that increase in mass with time. The SIMPOL.1 group contribution method can estimate the vapor pressure of these detected compounds, informing the expected composition of aerosols from condensation of larger species. At these experimental conditions, compounds with molecular weights greater than 350 g/mol are expected to be at least 50% in the particle phase and suggest that the complex, unsaturated organic nitrogen compounds formed would play an important role in aerosol composition. When considering Titan-like temperatures, the SIMPOL.1 method calculates that compounds with molecular weights greater than or equal to 130 g/mol would be more than 50% in the aerosols. Our results suggest that that the types of molecules contributing to aerosol formation varies with atmospheric temperature. The SIMPOL.1 method and CIMS experiments are widely applicable to exoplanetary atmospheres and can be used to inform models in determining exoplanet habitability.