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As the closest transiting hot Jupiter to Earth, HD 189733b has been the benchmark planet for atmospheric characterization 1-3 . It has also been the anchor point for much of our theoretical understanding of exoplanet atmospheres from composition 4 , chemistry 5,6 , aerosols 7 to atmospheric dynamics 8 , escape 9 and modelling techniques 10,11 . Previous studies of HD 189733b have detected carbon and oxygen-bearing molecules H 2 O and CO (refs.  12,13 ) in the atmosphere. The presence of CO 2 and CH 4 has been claimed 14,15 but later disputed 12,16,17 . The inferred metallicity based on these measurements, a key parameter in tracing planet formation locations 18 , varies from depletion 19,20 to enhancement 21,22 , hindered by limited wavelength coverage and precision of the observations. Here we report detections of H 2 O (13.4σ), CO 2 (11.2σ), CO (5σ) and H 2 S (4.5σ) in the transmission spectrum (2.4-5.0 μm) of HD 189733b. With an equilibrium temperature of about 1,200 K, H 2 O, CO and H 2 S are the main reservoirs for oxygen, carbon and sulfur. Based on the measured abundances of these three main volatile elements, we infer an atmospheric metallicity of three to five times stellar. The upper limit on the methane abundance at 5σ is 0.1 ppm, which indicates a low carbon-to-oxygen ratio (<0.2), suggesting formation through the accretion of water-rich icy planetesimals. The low oxygen-to-sulfur and carbon-to-sulfur ratios also support the planetesimal accretion formation pathway 23 ., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Interactions between exoplanetary atmospheres and internal properties have long been proposed to be drivers of the inflation mechanisms of gaseous planets and apparent atmospheric chemical disequilibrium conditions 1 . However, transmission spectra of exoplanets have been limited in their ability to observationally confirm these theories owing to the limited wavelength coverage of the Hubble Space Telescope (HST) and inferences of single molecules, mostly H 2 O (ref.  2 ). In this work, we present the panchromatic transmission spectrum of the approximately 750 K, low-density, Neptune-sized exoplanet WASP-107b using a combination of HST Wide Field Camera 3 (WFC3) and JWST Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI). From this spectrum, we detect spectroscopic features resulting from H 2 O (21σ), CH 4 (5σ), CO (7σ), CO 2 (29σ), SO 2 (9σ) and NH 3 (6σ). The presence of these molecules enables constraints on the atmospheric metal enrichment (M/H is 10-18× solar 3 ), vertical mixing strength (log 10 K zz  = 8.4-9.0 cm 2  s -1 ) and internal temperature (>345 K). The high internal temperature is suggestive of tidally driven inflation 4 acting on a Neptune-like internal structure, which can naturally explain the large radius and low density of the planet. These findings suggest that eccentricity-driven tidal heating is a critical process governing atmospheric chemistry and interior-structure inferences for most of the cool (<1,000 K) super-Earth-to-Saturn-mass exoplanet population., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

The abundances of main carbon- and oxygen-bearing gases in the atmospheres of giant exoplanets provide insights into atmospheric chemistry and planet formation processes 1,2 . Thermochemistry suggests that methane (CH 4 ) should be the dominant carbon-bearing species below about 1,000 K over a range of plausible atmospheric compositions 3 ; this is the case for the solar system planets 4 and has been confirmed in the atmospheres of brown dwarfs and self-luminous, directly imaged exoplanets 5 . However, CH 4 has not yet been definitively detected with space-based spectroscopy in the atmosphere of a transiting exoplanet 6-11 , but a few detections have been made with ground-based, high-resolution transit spectroscopy 12,13 including a tentative detection for WASP-80b (ref. 14 ). Here we report transmission and emission spectra spanning 2.4-4.0 μm of the 825 K warm Jupiter WASP-80b taken with the NIRCam instrument of the JWST, both of which show strong evidence of CH 4 at greater than 6σ significance. The derived CH 4 abundances from both viewing geometries are consistent with each other and with solar to sub-solar C/O and around five times solar metallicity, which is consistent with theoretical predictions 15-17 ., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Atmospheric metal enrichment (that is, elements heavier than helium, also called 'metallicity') is a key diagnostic of the formation of giant planets 1-3 . The giant planets of the Solar System show an inverse relationship between mass and both their bulk metallicities and atmospheric metallicities. Extrasolar giant planets also display an inverse relationship between mass and bulk metallicity 4 . However, there is significant scatter in the relationship and it is not known how atmospheric metallicity correlates with either planet mass or bulk metallicity. Here we show that the Saturn-mass exoplanet HD 149026b (refs. 5-9 ) has an atmospheric metallicity 59-276 times solar (at 1σ), which is greater than Saturn's atmospheric metallicity of roughly 7.5 times solar 10 at more than 4σ confidence. This result is based on modelling CO 2 and H 2 O absorption features in the thermal emission spectrum of the planet measured by the James Webb Space Telescope. HD 149026b is the most metal-rich giant planet known, with an estimated bulk heavy element abundance of 66 ± 2% by mass 11,12 . We find that the atmospheric metallicities of both HD 149026b and the Solar System giant planets are more correlated with bulk metallicity than planet mass., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability 1 . However, no unambiguous photochemical products have been detected in exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program 2,3 found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (SO 2 ) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 M J ) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of around 1,100 K (ref.  4 ). The most plausible way of generating SO 2 in such an atmosphere is through photochemical processes 5,6 . Here we show that the SO 2 distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by JWST transmission observations 7 with NIRSpec PRISM (2.7σ) 8 and G395H (4.5σ) 9 . SO 2 is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H 2 S) is destroyed. The sensitivity of the SO 2 feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of about 10× solar. We further point out that SO 2 also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations., (© 2023. The Author(s).)

The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy 1-4 . However, these efforts have been hampered by modelling degeneracies between composition and cloud properties that are caused by limited data quality 5-9 . Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. This spectrum spans 0.6-2.8 μm in wavelength and shows several water-absorption bands, the potassium resonance doublet and signatures of clouds. The precision and broad wavelength coverage of NIRISS/SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favouring a heavy-element enhancement ('metallicity') of about 10-30 times the solar value, a sub-solar carbon-to-oxygen (C/O) ratio and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are also best explained by wavelength-dependent, non-grey clouds with inhomogeneous coverageof the planet's terminator., (© 2023. The Author(s).)

Measuring the metallicity and carbon-to-oxygen (C/O) ratio in exoplanet atmospheres is a fundamental step towards constraining the dominant chemical processes at work and, if in equilibrium, revealing planet formation histories. Transmission spectroscopy (for example, refs. 1,2 ) provides the necessary means by constraining the abundances of oxygen- and carbon-bearing species; however, this requires broad wavelength coverage, moderate spectral resolution and high precision, which, together, are not achievable with previous observatories. Now that JWST has commenced science operations, we are able to observe exoplanets at previously uncharted wavelengths and spectral resolutions. Here we report time-series observations of the transiting exoplanet WASP-39b using JWST's Near InfraRed Camera (NIRCam). The long-wavelength spectroscopic and short-wavelength photometric light curves span 2.0-4.0 micrometres, exhibit minimal systematics and reveal well defined molecular absorption features in the planet's spectrum. Specifically, we detect gaseous water in the atmosphere and place an upper limit on the abundance of methane. The otherwise prominent carbon dioxide feature at 2.8 micrometres is largely masked by water. The best-fit chemical equilibrium models favour an atmospheric metallicity of 1-100-times solar (that is, an enrichment of elements heavier than helium relative to the Sun) and a substellar C/O ratio. The inferred high metallicity and low C/O ratio may indicate significant accretion of solid materials during planet formation (for example, refs. 3,4 , ) or disequilibrium processes in the upper atmosphere (for example, refs. 5,6 )., (© 2023. The Author(s).)

Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems 1,2 . Access to the chemical inventory of an exoplanet requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based 3-5 and high-resolution ground-based 6-8 facilities. Here we report the medium-resolution (R ≈ 600) transmission spectrum of an exoplanet atmosphere between 3 and 5 μm covering several absorption features for the Saturn-mass exoplanet WASP-39b (ref.  9 ), obtained with the Near Infrared Spectrograph (NIRSpec) G395H grating of JWST. Our observations achieve 1.46 times 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 (28.5σ) and H 2 O (21.5σ), and identify SO 2 as the source of absorption at 4.1 μm (4.8σ). Best-fit atmospheric models range between 3 and 10 times solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO 2 , underscore the importance of characterizing the chemistry in exoplanet atmospheres and showcase NIRSpec G395H as an excellent mode for time-series observations over this critical wavelength range 10 ., (© 2023. The Author(s).)