Abstract
The recent inference of sulfur dioxide (SO2) in the atmosphere of the hot (approximately 1,100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations1,2,3 suggests that photochemistry is a key process in high-temperature exoplanet atmospheres4. This is because of the low (<1 ppb) abundance of SO2 under thermochemical equilibrium compared with that produced from the photochemistry of H2O and H2S (1–10 ppm)4,5,6,7,8,9. However, the SO2 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 SO2 absorption bands at different wavelengths is needed to better constrain the SO2 abundance. Here we report the detection of SO2 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 SO2 of 0.5–25 ppm (1σ range), consistent with previous findings4. As well as SO2, 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.
| Original language | English |
|---|---|
| Pages (from-to) | 979-983 |
| Number of pages | 5 |
| Journal | Nature |
| Volume | 626 |
| Issue number | 8001 |
| Early online date | 17 Jan 2024 |
| DOIs | |
| Publication status | Published - 29 Feb 2024 |
Bibliographical note
Acknowledgments:This work is based on observations made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract no. NAS 5-03127 for JWST. These observations are associated with programme no. JWST-DD-2783, support for which was provided by NASA through a grant from the Space Telescope Science Institute. T.B. acknowledges funding support from the NASA Next Generation Space Telescope Flight Investigations programme (now JWST) through WBS 411672.07.05.05.03.02. J.K.B. is supported by a UKRI STFC Ernest Rutherford Fellowship (grant ST/T004479/1). J.T. is supported by the Eric and Wendy Schmidt AI in Science Postdoctoral Fellowship, a Schmidt Futures programme. J.Bl. acknowledges the support received in part from the NYUAD IT High Performance Computing resources, services and staff expertise. G.M. has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 895525 and from the Ariel Postdoctoral Fellowship Program of the Swedish National Space Agency (SNSA). B.-O.D. acknowledges support from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00046. E.A.M.V. acknowledges support from the Centre for Space and Habitability (CSH) and the NCCR PlanetS supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. Y.M. has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 101088557, N-GINE). M.Z. is a 51 Pegasi b fellow. L.W. and R.J.M. are NHFP Sagan fellows. We thank M. Marley for constructive comments.