학술논문
SO$_2$, silicate clouds, but no CH$_4$ detected in a warm Neptune
Document Type
Working Paper
Author
Dyrek, Achrène; Min, Michiel; Decin, Leen; Bouwman, Jeroen; Crouzet, Nicolas; Mollière, Paul; Lagage, Pierre-Olivier; Konings, Thomas; Tremblin, Pascal; Güdel, Manuel; Pye, John; Waters, Rens; Henning, Thomas; Vandenbussche, Bart; Martinez, Francisco Ardevol; Argyriou, Ioannis; Ducrot, Elsa; Heinke, Linus; Van Looveren, Gwenael; Absil, Olivier; Barrado, David; Baudoz, Pierre; Boccaletti, Anthony; Cossou, Christophe; Coulais, Alain; Edwards, Billy; Gastaud, René; Glasse, Alistair; Glauser, Adrian; Greene, Thomas P.; Kendrew, Sarah; Krause, Oliver; Lahuis, Fred; Mueller, Michael; Olofsson, Goran; Patapis, Polychronis; Rouan, Daniel; Royer, Pierre; Scheithauer, Silvia; Waldmann, Ingo; Whiteford, Niall; Colina, Luis; van Dishoeck, Ewine F.; Greve, Thomas; Ostlin, Göran; Ray, Tom P.; Wright, Gillian
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Abstract
WASP-107b is a warm ($\sim$740 K) transiting planet with a Neptune-like mass of $\sim$30.5 $M_{\oplus}$ and Jupiter-like radius of $\sim$0.94 $R_{\rm J}$, whose extended atmosphere is eroding. Previous observations showed evidence for water vapour and a thick high-altitude condensate layer in WASP-107b's atmosphere. Recently, photochemically produced sulphur dioxide (SO$_2$) was detected in the atmosphere of a hot ($\sim$1,200 K) Saturn-mass planet from transmission spectroscopy near 4.05 $\mu$m, but for temperatures below $\sim$1,000 K sulphur is predicted to preferably form sulphur allotropes instead of SO$_2$. Here we report the 9$\sigma$-detection of two fundamental vibration bands of SO$_2$, at 7.35 $\mu$m and 8.69 $\mu$m, in the transmission spectrum of WASP-107b using the Mid-Infrared Instrument (MIRI) of the JWST. This discovery establishes WASP-107b as the second irradiated exoplanet with confirmed photochemistry, extending the temperature range of exoplanets exhibiting detected photochemistry from $\sim$1,200 K down to $\sim$740 K. Additionally, our spectral analysis reveals the presence of silicate clouds, which are strongly favoured ($\sim$7$\sigma$) over simpler cloud setups. Furthermore, water is detected ($\sim$12$\sigma$), but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity.