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More than 4000 exoplanets have been discovered in last two decades, including a sample of terrestrial planets in the habitable zone of their host stars. New observing capabilities coming online over the next few years will provide opportunities for characterizing their atmospheres and assessing their potential habitability. Photochemical hazes are expected to form in these exoplanet atmospheres and impact our observations to those distant worlds. However, the formation processes of exoplanetary hazes and their physical/chemical properties are poorly understood.  We performed the first laboratory experiment to simulate photochemical haze formation in a broad range of temperate (<800 K) exoplanet atmospheres using the PHAZER chamber at JHU with one of two energy sources (AC glow plasma and UV photons). We studied the particle size distributions (He et al. 2018a, 2018b, He et al.2020a, 2020b) and the production rates (He et al. 2018a; Hörst et al. 2018a, He et al.2020a, 2020b) of solid haze particles that formed, as well as the gas and solid phase chemistry (He et al. 2019, He et al.2020a, 2020b, Moran et al. 2020, Vuitton et al. 2021). 

We find that the particle size is dependent on the experimental conditions, while the production rates are sensitive to atmospheric compositions (He et al. 2018a, 2018b, 2020; Hörst et al. 2018). Even a small amount of H2S can enrich the photochemistry and enhance haze production rate significantly (He et al. 2020a). We observed the photochemical formation of O2, sulfur and organic products in the gas phase, which have been considered as potential biosignatures but are produced abiotically in our experiments. Organic molecules are detected in both gas and solid phases, including potential prebiotic precursors (HCHO and HCN) and compounds with prebiotic molecular formulas, which could provide a source of organic materials for life to arise.

Cloud Nine Con | Chao He | Exploring Exoplanetary Hazes from Laboratory Simulations