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Abstract:

Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems. Access to an exoplanet's chemical inventory requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based and high-resolution ground-based facilities. Here we report the medium-resolution (R$\sim$600) transmission spectrum of an exoplanet atmosphere between 3-5 $\mu$m covering multiple absorption features for the Saturn-mass exoplanet WASP-39b, obtained with JWST NIRSpec G395H. Our observations achieve 1.46x photon precision, providing an average transit depth uncertainty of 221 ppm per spectroscopic bin, and present minimal impacts from systematic effects. We detect significant absorption from CO$_2$ (28.5$\sigma$) and H$_2$O (21.5$\sigma$), and identify SO$_2$ as the source of absorption at 4.1 $\mu$m (4.8$\sigma$). Best-fit atmospheric models range between 3 and 10x solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO$_2$, underscore the importance of characterising the chemistry in exoplanet atmospheres, and showcase NIRSpec G395H as an excellent mode for time series observations over this critical wavelength range.Comment: 44 pages, 11 figures, 3 tables. Resubmitted after revision to Natur

Abstract:

The study of isotopic ratios in planetary atmospheres gives an insight into the formation history and evolution of these objects. The more we can constrain these ratios, the better we can understand the history and future of our solar system. To help in this endeavour, we used Infrared Space Observatory Short Wavelength Spectrometer (ISO/SWS) Jupiter observations in the 793–1500 cm (Formula presented.) region together with the Nonlinear Optimal Estimator for MultivariatE Spectral analySIS (NEMESIS) radiative transfer suite to retrieve the temperature–pressure profile and the chemical abundances for various chemical species. We also used the 1500–2499 cm (Formula presented.) region to determine the cloud and aerosol structure of the upper troposphere. We obtained a best-fit simulated spectrum with (Formula presented.) for the 793–1500 cm (Formula presented.) region and (Formula presented.) for the 1500–2499 cm (Formula presented.) region. From the retrieved methane abundances, we obtained, within a 1 (Formula presented.) uncertainty, a (Formula presented.) C/ (Formula presented.) C ratio of 84 ± 27 and a D/H ratio of (3.5 ± 0.6) × 10 (Formula presented.), and these ratios are consistent with other published results from the literature.