SO2, silicate clouds, but no CH4 detected in a warm Neptune
Henning, Thomas; Östlin, Göran; Güdel, Manuel; Colina, Luis; Boccaletti, Anthony; Bouwman, Jeroen; Wright, Gillian; Kendrew, Sarah; Lagage, Pierre-Olivier; Vandenbussche, Bart; Mollière, Paul; Crouzet, Nicolas; Ducrot, Elsa; van Dishoeck, Ewine F.; Barrado, David; Decin, Leen; Dyrek, Achrène; Min, Michiel; Patapis, Polychronis; Whiteford, Niall; Absil, Olivier; Ray, Tom P.; Greene, Thomas P.; Waters, Rens; Edwards, Billy; Waldmann, Ingo; Argyriou, Ioannis; Lahuis, Fred; Mueller, Michael; Scheithauer, Silvia; Baudoz, Pierre; Rouan, Daniel; Cossou, Christophe; Pye, John; Olofsson, Goran; Glasse, Alistair; Royer, Pierre; Tremblin, Pascal; Ardevol Martinez, Francisco; Coulais, Alain; Gastaud, René; Krause, Oliver; Konings, Thomas; Heinke, Linus; van Looveren, Gwenael; Glauser, Adrian
France, Netherlands, Belgium, Germany, Austria, Switzerland, United Kingdom, Spain, United States, Sweden, Ireland
Abstract
WASP-107b is a warm (approximately 740 K) transiting planet with a Neptune-like mass of roughly 30.5 M⊕ and Jupiter-like radius of about 0.94 RJ (refs. 1,2), whose extended atmosphere is eroding3. Previous observations showed evidence for water vapour and a thick, high-altitude condensate layer in the atmosphere of WASP-107b (refs. 4,5). Recently, photochemically produced sulfur dioxide (SO2) was detected in the atmosphere of a hot (about 1,200 K) Saturn-mass planet from transmission spectroscopy near 4.05 μm (refs. 6,7), but for temperatures below about 1,000 K, sulfur is predicted to preferably form sulfur allotropes instead of SO2 (refs. 8-10). Here we report the 9σ detection of two fundamental vibration bands of SO2, at 7.35 μm and 8.69 μm, in the transmission spectrum of WASP-107b using the Mid-Infrared Instrument (MIRI) of JWST. This discovery establishes WASP-107b as the second irradiated exoplanet with confirmed photochemistry, extending the temperature range of exoplanets exhibiting detected photochemistry from about 1,200 K down to about 740 K. Furthermore, our spectral analysis reveals the presence of silicate clouds, which are strongly favoured (around 7σ) over simpler cloud set-ups. Furthermore, water is detected (around 12σ) but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity.