Abstract Being one of the first exoplanets observed by the James Webb Space Telescope, WASP-39 b has become an iconic target, and many transit spectra recorded with different instruments (NIRISS, NIRCAM, NIRSpec G395H, NIRSpec PRISM, and MIRI) are currently available, allowing in-depth studies of its atmosphere. We present here a novel approach to interpret WASP-39 b’s transit spectroscopic data, consisting of a multistep process where ab initio equilibrium chemistry models and blind retrievals are used iteratively to find physically robust, optimal solutions. Following this approach, we have identified a new scenario to explain WASP-39 b’s atmospheric composition, in which silicon-based chemistry plays a major role. In this scenario, SiO may explain the spectral absorption at 4.1 μ m, currently interpreted as being due to SO 2 . SiO and the other gas species identified by the retrieval models, i.e., H 2 O, CO 2 , Na, and K, are consistent with an atmosphere in chemical equilibrium with a temperature–pressure profile constrained by H 2 O and CO 2 absorption bands. In addition, silicate clouds and hazes can produce the spectral features observed by MIRI in the spectral window 5–12 μ m. While we advocate the need for more data, possibly at higher spectral resolution, to confirm our results for WASP-39 b’s atmospheric composition, we highlight a refined atmospheric retrieval strategy with preselection and post-reconstruction to guide the next generation of transit spectroscopy.
Ma et al. (Thu,) studied this question.