. 2023 Feb;614(7949):659-663.

doi: 10.1038/s41586-022-05677-y. Epub 2023 Jan 9.

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

Z Rustamkulov¹, D K Sing^{2

3}, S Mukherjee⁴, E M May⁵, J Kirk^{6

7}, E Schlawin⁸, M R Line⁹, C Piaulet¹⁰, A L Carter⁴, N E Batalha¹¹, J M Goyal¹², M López-Morales⁶, J D Lothringer¹³, R J MacDonald^{14

15}, S E Moran¹⁶, K B Stevenson⁵, H R Wakeford¹⁷, N Espinoza¹⁸, J L Bean¹⁹, N M Batalha⁴, B Benneke¹⁰, Z K Berta-Thompson²⁰, I J M Crossfield²¹, P Gao²², L Kreidberg²³, D K Powell²⁴, P E Cubillos²⁵, N P Gibson²⁶, J Leconte²⁷, K Molaverdikhani^{28

29}, N K Nikolov¹⁸, V Parmentier^{30

31}, P Roy¹⁰, J Taylor³², J D Turner¹⁵, P J Wheatley^{33

34}, K Aggarwal³⁵, E Ahrer^{33

34}, M K Alam²², L Alderson¹⁷, N H Allen³, A Banerjee³⁶, S Barat³⁷, D Barrado³⁸, J K Barstow³⁶, T J Bell³⁹, J Blecic^{40

41}, J Brande²¹, S Casewell⁴², Q Changeat^{18

43

44}, K L Chubb⁴⁵, N Crouzet⁴⁶, T Daylan⁴⁷, L Decin⁴⁸, J Désert³⁷, T Mikal-Evans²³, A D Feinstein^{19

36}, L Flagg¹⁵, J J Fortney⁴, J Harrington⁴⁹, K Heng²⁸, Y Hong¹⁵, R Hu^{50

51}, N Iro⁵², T Kataria⁵⁰, E M-R Kempton⁵³, J Krick⁵⁴, M Lendl⁵⁵, J Lillo-Box³⁸, A Louca⁴⁶, J Lustig-Yaeger⁵, L Mancini^{23

25

56}, M Mansfield⁸, N J Mayne⁵⁷, Y Miguel^{46

58}, G Morello^{59

60

61}, K Ohno⁴, E Palle⁵⁹, D J M Petit Dit de la Roche⁵⁵, B V Rackham^{62

63}, M Radica¹⁰, L Ramos-Rosado³, S Redfield⁶⁴, L K Rogers⁶⁵, E L Shkolnik⁹, J Southworth⁶⁶, J Teske²², P Tremblin⁶⁷, G S Tucker⁶⁸, O Venot⁶⁹, W C Waalkes⁷⁰, L Welbanks⁹, X Zhang⁷¹, S Zieba^{23

46}

Affiliations

¹ Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA. zafar@jhu.edu.
² Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
³ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA.
⁴ Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA.
⁵ Johns Hopkins APL, Laurel, MD, USA.
⁶ Center for Astrophysics, Harvard and Smithsonian, Cambridge, MA, USA.
⁷ Department of Physics, Imperial College London, London, UK.
⁸ Steward Observatory, University of Arizona, Tucson, AZ, USA.
⁹ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
¹⁰ Institute of Research on Exoplanets, Department of Physics, University of Montreal, Montreal, Québec, Canada.
¹¹ NASA Ames Research Center, Moffett Field, CA, USA.
¹² School of Earth and Planetary Sciences, National Institute of Science Education and Research (NISER), HBNI, Jatani, India.
¹³ Department of Physics, Utah Valley University, Orem, UT, USA.
¹⁴ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA.
¹⁵ Department of Astronomy and Carl Sagan Institute, Cornell University, Ithaca, NY, USA.
¹⁶ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
¹⁷ School of Physics, University of Bristol, HH Wills Physics Laboratory, Bristol, UK.
¹⁸ Space Telescope Science Institute, Baltimore, MD, USA.
¹⁹ Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
²⁰ Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO, USA.
²¹ Department of Physics and Astronomy, University of Kansas, Lawrence, KS, USA.
²² Earth and Planets Laboratory, Carnegie Institution of Washington, Washington, DC, USA.
²³ Max Planck Institute for Astronomy, Heidelberg, Germany.
²⁴ Harvard and Smithsonian, Center for Astrophysics, Cambridge, MA, USA.
²⁵ INAF - Astrophysics Observatory at Turin, Turin, Italy.
²⁶ School of Physics, Trinity College Dublin, Dublin, Ireland.
²⁷ Laboratoire d'Astrophysique de Bordeaux, CNRS, Université de Bordeaux, Pessac, France.
²⁸ University Observatory Munich, Ludwig Maximilian University, Munich, Germany.
²⁹ Exzellenzcluster Origins, Garching, Germany.
³⁰ Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France.
³¹ Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK.
³² Department of Physics, University of Oxford, Oxford, UK.
³³ Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK.
³⁴ Department of Physics, University of Warwick, Coventry, UK.
³⁵ Indian Institute of Technology, Indore, Indore, India.
³⁶ School of Physical Sciences, The Open University, Milton Keynes, UK.
³⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, the Netherlands.
³⁸ Centre for Astrobiology (CSIC-INTA), European Space Astronomy Centre Campus, University of Maria de Maeztu, Madrid, Spain.
³⁹ BAER Institute, NASA Ames Research Center, Moffet Field, Mountain View, CA, USA.
⁴⁰ New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
⁴¹ Center for Astro, Particle and Planetary Physics (CAP3), New York University Abu Dhabi, Abu Dhabi, UAE.
⁴² School of Physics and Astronomy, University of Leicester, Leicester, UK.
⁴³ European Space Agency (ESA), ESA Baltimore Office, Baltimore, MD, USA.
⁴⁴ Department of Physics and Astronomy, University College London, London, UK.
⁴⁵ Centre for Exoplanet Science, University of St Andrews, St Andrews, UK.
⁴⁶ Leiden Observatory, Leiden University, Leiden, the Netherlands.
⁴⁷ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA.
⁴⁸ Department of Physics and Astronomy, KU Leuven, Leuven, Belgium.
⁴⁹ Planetary Science Group, Department of Physics and Florida Space Institute, University of Central Florida, Orlando, FL, USA.
⁵⁰ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
⁵¹ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
⁵² Institute for Astrophysics, University of Vienna, Vienna, Austria.
⁵³ Department of Astronomy, University of Maryland, College Park, MD, USA.
⁵⁴ California Institute of Technology, IPAC, Pasadena, CA, USA.
⁵⁵ Department of Astronomy, University of Geneva, Geneva, Switzerland.
⁵⁶ Department of Physics, University of Rome 'Tor Vergata', Rome, Italy.
⁵⁷ Department of Physics and Astronomy, Faculty of Environment, Science and Economy, University of Exeter, Exeter, UK.
⁵⁸ SRON Netherlands Institute for Space Research, Leiden, the Netherlands.
⁵⁹ Institute for Astrophysics of Canarias (IAC), La Laguna, Tenerife, Spain.
⁶⁰ Department of Astrophysics, University of La Laguna, La Laguna, Tenerife, Spain.
⁶¹ INAF Äì Palermo Astronomical Observatory, Palermo, Italy.
⁶² Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁶³ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁶⁴ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT, USA.
⁶⁵ Institute of Astronomy, University of Cambridge, Cambridgeshire, UK.
⁶⁶ Astrophysics Group, Keele University, Staffordshire, UK.
⁶⁷ UVSQ, CNRS, CEA, Maison de la Simulation, Université Paris-Saclay, Gif-sur-Yvette, France.
⁶⁸ Department of Physics, Brown University, Providence, RI, USA.
⁶⁹ Université de Paris Cité and Univ Paris Est Creteil, CNRS, LISA, Paris, France.
⁷⁰ Astrophysics and Planetary Sciences, University of Colorado Boulder, Boulder, CO, USA.
⁷¹ Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, USA.

PMID: 36623548
PMCID: PMC9946832
DOI: 10.1038/s41586-022-05677-y

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

Z Rustamkulov et al. Nature. 2023 Feb.

. 2023 Feb;614(7949):659-663.

doi: 10.1038/s41586-022-05677-y. Epub 2023 Jan 9.

Authors

Affiliations

¹ Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA. zafar@jhu.edu.
² Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
³ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA.
⁴ Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA.
⁵ Johns Hopkins APL, Laurel, MD, USA.
⁶ Center for Astrophysics, Harvard and Smithsonian, Cambridge, MA, USA.
⁷ Department of Physics, Imperial College London, London, UK.
⁸ Steward Observatory, University of Arizona, Tucson, AZ, USA.
⁹ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
¹⁰ Institute of Research on Exoplanets, Department of Physics, University of Montreal, Montreal, Québec, Canada.
¹¹ NASA Ames Research Center, Moffett Field, CA, USA.
¹² School of Earth and Planetary Sciences, National Institute of Science Education and Research (NISER), HBNI, Jatani, India.
¹³ Department of Physics, Utah Valley University, Orem, UT, USA.
¹⁴ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA.
¹⁵ Department of Astronomy and Carl Sagan Institute, Cornell University, Ithaca, NY, USA.
¹⁶ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
¹⁷ School of Physics, University of Bristol, HH Wills Physics Laboratory, Bristol, UK.
¹⁸ Space Telescope Science Institute, Baltimore, MD, USA.
¹⁹ Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
²⁰ Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO, USA.
²¹ Department of Physics and Astronomy, University of Kansas, Lawrence, KS, USA.
²² Earth and Planets Laboratory, Carnegie Institution of Washington, Washington, DC, USA.
²³ Max Planck Institute for Astronomy, Heidelberg, Germany.
²⁴ Harvard and Smithsonian, Center for Astrophysics, Cambridge, MA, USA.
²⁵ INAF - Astrophysics Observatory at Turin, Turin, Italy.
²⁶ School of Physics, Trinity College Dublin, Dublin, Ireland.
²⁷ Laboratoire d'Astrophysique de Bordeaux, CNRS, Université de Bordeaux, Pessac, France.
²⁸ University Observatory Munich, Ludwig Maximilian University, Munich, Germany.
²⁹ Exzellenzcluster Origins, Garching, Germany.
³⁰ Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France.
³¹ Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK.
³² Department of Physics, University of Oxford, Oxford, UK.
³³ Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK.
³⁴ Department of Physics, University of Warwick, Coventry, UK.
³⁵ Indian Institute of Technology, Indore, Indore, India.
³⁶ School of Physical Sciences, The Open University, Milton Keynes, UK.
³⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, the Netherlands.
³⁸ Centre for Astrobiology (CSIC-INTA), European Space Astronomy Centre Campus, University of Maria de Maeztu, Madrid, Spain.
³⁹ BAER Institute, NASA Ames Research Center, Moffet Field, Mountain View, CA, USA.
⁴⁰ New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
⁴¹ Center for Astro, Particle and Planetary Physics (CAP3), New York University Abu Dhabi, Abu Dhabi, UAE.
⁴² School of Physics and Astronomy, University of Leicester, Leicester, UK.
⁴³ European Space Agency (ESA), ESA Baltimore Office, Baltimore, MD, USA.
⁴⁴ Department of Physics and Astronomy, University College London, London, UK.
⁴⁵ Centre for Exoplanet Science, University of St Andrews, St Andrews, UK.
⁴⁶ Leiden Observatory, Leiden University, Leiden, the Netherlands.
⁴⁷ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA.
⁴⁸ Department of Physics and Astronomy, KU Leuven, Leuven, Belgium.
⁴⁹ Planetary Science Group, Department of Physics and Florida Space Institute, University of Central Florida, Orlando, FL, USA.
⁵⁰ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
⁵¹ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
⁵² Institute for Astrophysics, University of Vienna, Vienna, Austria.
⁵³ Department of Astronomy, University of Maryland, College Park, MD, USA.
⁵⁴ California Institute of Technology, IPAC, Pasadena, CA, USA.
⁵⁵ Department of Astronomy, University of Geneva, Geneva, Switzerland.
⁵⁶ Department of Physics, University of Rome 'Tor Vergata', Rome, Italy.
⁵⁷ Department of Physics and Astronomy, Faculty of Environment, Science and Economy, University of Exeter, Exeter, UK.
⁵⁸ SRON Netherlands Institute for Space Research, Leiden, the Netherlands.
⁵⁹ Institute for Astrophysics of Canarias (IAC), La Laguna, Tenerife, Spain.
⁶⁰ Department of Astrophysics, University of La Laguna, La Laguna, Tenerife, Spain.
⁶¹ INAF Äì Palermo Astronomical Observatory, Palermo, Italy.
⁶² Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁶³ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁶⁴ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT, USA.
⁶⁵ Institute of Astronomy, University of Cambridge, Cambridgeshire, UK.
⁶⁶ Astrophysics Group, Keele University, Staffordshire, UK.
⁶⁷ UVSQ, CNRS, CEA, Maison de la Simulation, Université Paris-Saclay, Gif-sur-Yvette, France.
⁶⁸ Department of Physics, Brown University, Providence, RI, USA.
⁶⁹ Université de Paris Cité and Univ Paris Est Creteil, CNRS, LISA, Paris, France.
⁷⁰ Astrophysics and Planetary Sciences, University of Colorado Boulder, Boulder, CO, USA.
⁷¹ Department of Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, USA.

PMID: 36623548
PMCID: PMC9946832
DOI: 10.1038/s41586-022-05677-y

Abstract

Transmission spectroscopy^1-3 of exoplanets has revealed signatures of water vapour, aerosols and alkali metals in a few dozen exoplanet atmospheres^4,5. However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species-in particular the primary carbon-bearing molecules^6,7. Here we report a broad-wavelength 0.5-5.5 µm atmospheric transmission spectrum of WASP-39b⁸, a 1,200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with the JWST NIRSpec's PRISM mode⁹ as part of the JWST Transiting Exoplanet Community Early Release Science Team Program^10-12. We robustly detect several chemical species at high significance, including Na (19σ), H₂O (33σ), CO₂ (28σ) and CO (7σ). The non-detection of CH₄, combined with a strong CO₂ feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4 µm is best explained by SO₂ (2.7σ), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST's sensitivity to a rich diversity of exoplanet compositions and chemical processes.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interests.

Figures

**Fig. 1. The light curve of WASP-39b observed by JWST NIRSpec PRISM.**
a, The normalized white light curve created by integrating over all wavelengths using the FIREFLy reduction. b, The binned time series (with 30 integrations per time bin) of the relative flux for each wavelength. A constant 200 ppm per hour linear trend through time has been removed from the white light curve and each spectral channel for visual clarity.

**Fig. 2. Normalized spectrophotometric light curves for the JWST-PRISM transit of WASP-39b.**
The light curves were created by summing over wide wavelength channels (wavelength ranges indicated on the plot). Overplotted on each light curve are their best-fit models, which include a transit model and detector systematics. Light curve systematics have not been removed from the data.

**Fig. 3. WASP-39b transmission spectral measurements.**
A comparison of the JWST transmission spectra obtained from the four independent reductions considered in this work (coloured points), which are all in broad agreement. Previous measurements from HST, VLT and Spitzer are also shown (grey) along with our fiducial best-fit spectrum model from the PICASO 3.0 grid (black line). All the transmission spectral data have 1 − σ error bars shown. The saturated region of the detector is indicated (grey bar) with the shading representative of the level of saturation (also Extended Data Fig. 6). Different reductions are presented on slightly different wavelength grids for visual purposes, the original resolution each reduction used is discussed in the Methods.

**Fig. 4. The JWST-PRISM transmission spectrum of WASP-39b with key contributions to the atmospheric spectrum.**
The black points with error bars correspond to the measured FIREFLy transit depths of the spectrophotometric light curves at different wavelengths. The best-fitting model spectrum from the PICASO 3.0 grid is shown as the grey line and the coloured regions correspond to the chemical opacity contributions at specific wavelengths. The best-fitting 1D RCTE model corresponds to a super-solar metallicity and super-solar carbon-to-oxygen ratio with moderate cloud opacity (Methods). The PRISM transmission spectrum is explained by contributions from Na (19σ), H₂O (33σ), CO₂ (28σ), CO (7σ), SO₂ (2.7σ) and clouds (21σ). The data do not provide evidence of CH₄, H₂S and K absorption (Methods). Also, note that the detector was saturated to varying degrees between 0.8 and 1.9 µm. As before, the error bars are 1 − σ standard deviations.

**Extended Data Fig. 1. A comparison of the extracted 1D spectrophotometry across the four reductions.**
Plotted is the spectrophotometry with time on the x-axis and wavelength on the y-axis, with color indicating the relative flux. The transit is visible as a dark band in the middle of the observation. All four reductions show nearly identical noise properties.

**Extended Data Fig. 2. Demonstration of the impact of saturation.**
Shown are the group-level median frames from the uncalibrated data products across the entire integration. The dashed blue line represents the empirically derived saturation level, with the orange dotted line representing 85% saturation, the level adopted in the Eureka! reduction. Grey shaded regions represent columns that reach 85% full well in a given group.

**Extended Data Fig. 3. The wavelength-dependent central transit time in seconds.**
Structure is apparent–the prominent water and carbon dioxide absorption features at 2.7 µm and 4.2 µm, respectively, appear to arrive ∼20 s after the optical continuum. A slope is also apparent from the blue side to the red. The error bars are 1-σ standard deviations.

**Extended Data Fig. 4. A summary of the positional shifts of the trace, the wavelength-dependent light curve scatter, and the transit depth noise.**
(**Top**) The X- and Y-shift vectors as measured by 1D cross correlation with FIREFLy. (**Middle**) The residual spectrophotometric light curves are shown for four representative spectral channels spanning the PRISM wavelength range with no temporal binning. The residual scatter is approximately Gaussian for each, as indicated by the histogram on the right y-axis. We validate this by performing Anderson-Darling tests on the residuals of the spectral and white-light curves, and find that all of the Anderson-Darling test statistics lie below the respective critical values 1% significance level. Therefore, we find that there is not sufficient evidence that the residuals are not normally distributed. (**Bottom**) The top two purple curves show the expected and measured normalised light curve root mean square (RMS) residuals, with no temporal binning. Longward of 2 µm, the scatter in each light curve matches well with the expected noise as estimated by the jwst pipeline, which is dominated by photon noise. This agreement indicates the majority of the light curves reach near the photon limit. The transit depth uncertainties are also plotted below, including the white noise (blue, σ_w), red noise (red, σ_red), and total noise components (grey, σ_tot). Some wavelength bins have enhanced red noise, but the majority of the transmission spectrum is consistent with minimal red noise from residual systematic errors. The wavelengths affected by detector saturation are indicated by the grey shaded bar, with darker colors corresponding to quicker saturation. The colored dots are the measured RMS values from the light curves shown in the top panel.

**Extended Data Fig. 5. Empirically derived stellar limb darkening coefficients fit with a quadratic law.**
a, the fit u₊ coefficients (black) along with the theoretically predicted values derived from a 3D stellar model (red). The theoretical u₊ values with a constant offset of −0.065 ± 0.022 (purple) is also shown. The theoretical models predict the wavelength-to-wavelength shape of u₊ well. As u₊ is directly related to the intensity of the star at the stellar limb ref. , these findings suggest WASP-39A is 6% brighter at the limb than models predict. b, similar as a, but for the u₋ coefficient. As the shape of the derived coefficients differs from the model prediction, u₋ was left free to vary in the transmission spectral fits. The error bars are 1-σ standard deviations.

**Extended Data Fig. 6. Comparison of the JWST NIRSpec PRISM data (black) to HST and VLT data from ref. ^, and WHT data from ref. , respectively.**
The JWST spectrum was derived with the limb darkening fixed to the same 3D stellar model as in to aid comparisons. With fixed limb darkening, the JWST transmission spectrum has lower overall transit depths especially at optical wavelengths. The broadband spectrum from the two space telescopes compares well, including the amplitude of the 1.4 µm water feature first observed by HST/WFC3 and the Na feature near 0.6 µm observed by HST/STIS. The error bars are 1-σ standard deviations.

**Extended Data Fig. 7. Best-fit models from ScCHIMERA, PICASO 3.0, ATMO, and Phoenix 1D RCTE model grids for WASP-39b.**
The FIREFLy reduction is overlaid in the top panel. The top left inset panel shows the data and the models between 0.5—1.2 µm. All these models prefer super-solar atmospheric metallicities and cloudy atmospheres for WASP-39 b. The C/O ratio estimated by these models lies in the range 0.6– 0.7. Additional SO₂ was injected in the PICASO 3.0 and ScCHIMERA grids to estimate the abundance of SO₂ required to explain the 4.0 µm feature, in a Bayesian framework. The ATMO and PHOENIX models are shown without any additionally injected SO₂ to emphasize that RCTE models do not predict such an SO₂ feature and chemical disequilibrium effects are required to explain the observed feature. The bottom panel shows the residuals from each best-fit model divided by the noise in the transit depth as a function of wavelength. The error bars are 1-σ standard deviations.

**Extended Data Fig. 8. Each panel shows the residual spectrum of a particular gas.**
This residual spectrum was obtained by removing one gas at a time from the best-fit model atmosphere and subtracting the recalculated model transmission spectrum without that gas from the data. This residual spectrum was then fitted with a Gaussian distribution (and a Voigt profile for Na) and a constant offset, in a Bayesian framework. The median fit (solid lines) along with the 1σ and 2σ confidence intervals are shown with shaded red and blue regions for the Gaussian fits and the constant offset fits, respectively. The Bayes factor between the two functional fits was used to determine the detection significance of each gas. Note that the wavelength range covered in each panel is different. The error bars are 1-σ standard deviations.

**Extended Data Fig. 9. Models of varying metallicity (top) and C/O ratio (bottom) compared to the FIREFLy reduction.**
A comparison of cloud-free PICASO 3.0 RCTE models across a span of metallicities with the best-fit C/O ratio (0.68) is shown in the top panel. Each line coloured from faded to deep pink represents models with different metallicities between sub-solar to super-solar values. The simultaneous lack of a prominent CH₄ feature at 2.3 and 3.3 µm and the presence of a strong CO₂ feature indicate that the observations disfavor a low-metallicity atmosphere. The bottom panel shows transmission spectrum models with different C/O ratios from sub-solar to super-solar values at 10×solar metallicity compared with the observed spectrum. The cloudy best-fit model obtained with the grid retrieval framework also has been shown in both the panels with the grey line. As before, the errorbars are 1σ standard deviations.

**Extended Data Fig. 10. The wavelength-dependent contribution function.**
The shaded regions highlight the parts of the atmosphere probed by the observed transmission data as a function of wavelength, as calculated from the best-fit model. This shows that the data mostly probe pressure ranges between 0.1 to 2 mbars. The CO₂ feature shows contribution at pressures approaching a microbar. The various shaded lines in pink show the volume mixing ratio of CH₄ (upper x-axis), from thermochemical equilibrium models, with different atmospheric metallicities at the best-fit C/O ratio of 0.68.

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Comment in

JWST opens a window on exoplanet skies.
Seidel JV, Nielsen LD, Sarkar S. Seidel JV, et al. Nature. 2023 Feb;614(7949):632-633. doi: 10.1038/d41586-023-00394-6. Nature. 2023. PMID: 36792896 No abstract available.

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Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

Affiliations

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

Comment in

References

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