Journal Article

SO2, silicate clouds, but no CH4 detected in a warm Neptune

Mollière, Paul, Henning, Thomas, Mueller, Michael, Barrado, David, Baudoz, Pierre, Ray, Tom P., Decin, Leen, Lahuis, Fred, Östlin, Göran, Ducrot, Elsa, Krause, Oliver, Wright, Gillian, Vandenbussche, Bart, Crouzet, Nicolas, Greene, Thomas P., Royer, Pierre, Waters, Rens, Argyriou, Ioannis, Rouan, Daniel, Coulais, Alain, Gastaud, René, Pye, John, Boccaletti, Anthony, Whiteford, Niall, Tremblin, Pascal, Kendrew, Sarah, Olofsson, Goran, Dyrek, Achrène, Güdel, Manuel, van Looveren, Gwenael, Cossou, Christophe, Patapis, Polychronis, Min, Michiel, Glasse, Alistair, Colina, Luis, Absil, Olivier, Edwards, Billy, Glauser, Adrian, Scheithauer, Silvia, Bouwman, Jeroen, Heinke, Linus, Ardevol Martinez, Francisco, Konings, Thomas, van Dishoeck, Ewine F., Lagage, Pierre-Olivier, Waldmann, Ingo

2024

Overview

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  R J (refs.  1 , 2 ), whose extended atmosphere is eroding 3 . 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 (SO 2 ) 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 SO 2 (refs.  8 – 10 ). Here we report the 9 σ detection of two fundamental vibration bands of SO 2 , 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 7 σ ) over simpler cloud set-ups. Furthermore, water is detected (around 12 σ ) but methane is not. These findings provide evidence of disequilibrium chemistry and indicate a dynamically active atmosphere with a super-solar metallicity. The JWST MIRI transmission spectrum of WASP-107b, a transiting planet with Neptune-like mass and Jupiter-like radius, shows observations of sulfur dioxide and silicate clouds but no methane in its atmosphere, providing evidence of disequilibrium chemistry and active photochemistry.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/33/445/823 / 639/33/445/824 / 639/33/445/846 / 639/33/445/862 / Altitude / Astrophysics / Atmosphere / Atmospheric and Oceanic Physics / Aérospatiale, astronomie & astrophysique / Clouds / Earth and Planetary Astrophysics / Eddy diffusion / Equilibrium / Extrasolar planets / Free radicals / Gas giant planets / Gravity / High altitude / Humanities and Social Sciences / Hydrogen sulfide / Metallicity / Methane / multidisciplinary / Oxidation / Photochemicals / Photochemistry / Photolysis / Physical, chemical, mathematical & earth Sciences / Physics / Physique, chimie, mathématiques & sciences de la terre / Science / Science (multidisciplinary) / Sciences of the Universe / Space science, astronomy & astrophysics / Space telescopes / Sulfur / Sulfur dioxide / Temperature