Sulfur dioxide in the mid-infrared transmission spectrum of WASP-39b
Diana Powell, Adina D. Feinstein, Elspeth K. H. Lee, Michael Zhang, Shang‐Min Tsai, Jake Taylor, James Kirk, Taylor J. Bell, J. K. Barstow, Peter Gao, Jacob L. Bean, Jasmina Blecic, K. L. Chubb, Ian J. M. Crossfield, Sean Jordan, Daniel Kitzmann, Sarah E. Moran, Giuseppe Morello, Julianne I. Moses, Luis Welbanks, Jeehyun Yang, Xi Zhang, Eva-Maria Ahrer, Aaron Bello-Arufe, Jonathan Brande, S. L. Casewell, Nicolas Crouzet, Patricio E. Cubillos, Brice-Olivier Demory, Achrène Dyrek, Laura Flagg, Renyu Hu, Julie Inglis, K. Jones, Laura Kreidberg, Mercedes López‐Morales, Pierre-Olivier Lagage, E. A. Meier Valdés, Yamila Miguel, Vivien Parmentier, Anjali A. A. Piette, Benjamin V. Rackham, Michael Radica, Seth Redfield, Kevin B. Stevenson, Hannah R. Wakeford, Keshav Aggarwal, Munazza K. Alam, Natalie M. Batalha, Natasha E. Batalha, Björn Benneke, Zach K. Berta-Thompson, Ryan P. Brady, C. Cáceres, Aarynn L. Carter, Jean-Michel Désert, Joseph Harrington, Nicolas Iro, Michael Line, Joshua D. Lothringer, Ryan J. MacDonald, L. Mancini, Karan Molaverdikhani, Sagnick Mukherjee, Matthew C. Nixon, A. Oza, Ε. Πάλλη, Zafar Rustamkulov, David K. Sing, Maria E. Steinrueck, Olivia Vénot, P. J. Wheatley, S. N. Yurchenko
Abstract
Abstract The recent inference of sulfur dioxide (SO 2 ) in the atmosphere of the hot (approximately 1,100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations 1–3 suggests that photochemistry is a key process in high-temperature exoplanet atmospheres 4 . This is because of the low (<1 ppb) abundance of SO 2 under thermochemical equilibrium compared with that produced from the photochemistry of H 2 O and H 2 S (1–10 ppm) 4–9 . However, the SO 2 inference was made from a single, small molecular feature in the transmission spectrum of WASP-39b at 4.05 μm and, therefore, the detection of other SO 2 absorption bands at different wavelengths is needed to better constrain the SO 2 abundance. Here we report the detection of SO 2 spectral features at 7.7 and 8.5 μm in the 5–12-μm transmission spectrum of WASP-39b measured by the JWST Mid-Infrared Instrument (MIRI) Low Resolution Spectrometer (LRS) 10 . Our observations suggest an abundance of SO 2 of 0.5–25 ppm (1 σ range), consistent with previous findings 4 . As well as SO 2 , we find broad water-vapour absorption features, as well as an unexplained decrease in the transit depth at wavelengths longer than 10 μm. Fitting the spectrum with a grid of atmospheric forward models, we derive an atmospheric heavy-element content (metallicity) for WASP-39b of approximately 7.1–8.0 times solar and demonstrate that photochemistry shapes the spectra of WASP-39b across a broad wavelength range.