Sulfur dioxide in the mid-infrared transmission spectrum of WASP-39b.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 38232945.
- Also identified by DOI 10.1038/s41586-024-07040-9 and PMC identifier 10901732.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The recent inference of sulfur dioxide (SO<sub>2</sub>) in the atmosphere of the hot (approximately 1,100 K), Saturn-mass exoplanet WASP-39b from near-infrared JWST observations<sup>1-3</sup> suggests that photochemistry is a key process in high-temperature exoplanet atmospheres<sup>4</sup>. This is because of the low (<1 ppb) abundance of SO<sub>2</sub> under thermochemical equilibrium compared with that produced from the photochemistry of H<sub>2</sub>O and H<sub>2</sub>S (1-10 ppm)<sup>4-9</sup>. However, the SO<sub>2</sub> 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<sub>2</sub> absorption bands at different wavelengths is needed to better constrain the SO<sub>2</sub> abundance. Here we report the detection of SO<sub>2</sub> 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)<sup>10</sup>. Our observations suggest an abundance of SO<sub>2</sub> of 0.5-25 ppm (1σ range), consistent with previous findings<sup>4</sup>. As well as SO<sub>2</sub>, 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.