A large range of haziness conditions in hot-Jupiter atmospheres

Abstract

We present a study of photochemical hazes of exoplanet atmospheres based on a self-consistent model including haze microphysics, disequilibrium chemistry, and radiative feedbacks. We derive the haze properties required to match Hubble Space Telescope observations of 10 hot-Jupiters. HAT-P-12b, HD-189733b, HD-209458b, and WASP-6b require haze mass fluxes between 5 × 10^-15 and 9 × 10^-12 g cm^-2 s^-1 to match the observations. WASP-12b and WASP-19b with equilibrium temperatures above 2000 K are incompatible with the presence of haze and are better fitted by heavy metals. HAT-P-1b and WASP-31b do not show clear evidence for the presence of hazes with upper mass fluxes of 10^-15 and 10^-16 g cm^-2 s^-1, respectively, while WASP-17b and WASP-39b present an upper mass flux limit of 10^-16 g cm^-2 s^-1. We discuss the implications of the self-consistent model and we derive upper limits for the haze abundances based on photochemistry results. Our results suggest HCN as the main haze precursor up to 1300 K effective temperatures and CO above. Our derived haze mass fluxes based on the fit to the observations are consistent with the photochemistry with formation yields up to ~6.4 per cent. Disequilibrium chemistry has negligible impact on the spectra considering the low-resolution observations used but impacts the chemical composition and temperature profiles. We find that hazes produce hotter upper atmosphere temperatures with a detectable impact on the spectra. Clouds may have implications for interpreting the transit spectra of HD-209458b, WASP-31b, and WASP-39b. Nevertheless, the presence of silicate and iron clouds is expected in all studied atmospheres except WASP-12b and WASP-19b.