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Harvard ADS: Quartz Clouds in the Dayside Atmosphere of the Quintessential Hot Jupiter HD 189733 b

Paper abstract: Recent mid-infrared observations with JWST/MIRI have resulted in the first direct detections of absorption features from silicate clouds in the transmission spectra of two transiting exoplanets, WASP-17 b and WASP-107 b. In this paper, we measure the mid-infrared (5-12 \mum) dayside emission spectrum of the benchmark hot Jupiter HD 189733 b with MIRI LRS by combining data from two secondary eclipse observations. We confirm the previous detection of H_2O absorption at 6.5 \mum from Spitzer/IRS and additionally detect H_2S as well as an absorption feature at 8.7 \mum in both secondary eclipse observations. The excess absorption at 8.7 \mum can be explained by the presence of small (~0.01 \mum) grains of SiO_2[s] in the uppermost layers of HD 189733 b's dayside atmosphere. This is the first direct detection of silicate clouds in HD 189733 b's atmosphere, and the first detection of a distinct absorption feature from silicate clouds on the day side of any hot Jupiter. We find that models including SiO_2[s] are preferred by 6-7\sigma over clear models and those with other potential cloud species. The high altitude location of these silicate particles is best explained by formation in the hottest regions of HD 189733 b's dayside atmosphere near the substellar point. We additionally find that HD 189733 b's emission spectrum longward of 9 \mum displays residual features not well captured by our current atmospheric models. When combined with other JWST observations of HD 189733 b's transmission and emission spectrum at shorter wavelengths, these observations will provide us with the most detailed picture to date of the atmospheric composition and cloud properties of this benchmark hot Jupiter.