Early Release Science of the exoplanet WASP-39b with JWST NIRSpec G395H

Lili Alderson¹, Hannah R Wakeford², Munazza K Alam³, Natasha E Batalha⁴, Joshua D Lothringer⁵, Jea Adams Redai⁶, Saugata Barat⁷, Jonathan Brande⁸, Mario Damiano⁹, Tansu Daylan¹⁰, Néstor Espinoza^{11

12}, Laura Flagg^{13

14}, Jayesh M Goyal¹⁵, David Grant¹⁶, Renyu Hu^{9

17}, Julie Inglis¹⁷, Elspeth K H Lee¹⁸, Thomas Mikal-Evans¹⁹, Lakeisha Ramos-Rosado¹², Pierre-Alexis Roy^{20

21}, Nicole L Wallack^{3

17}, Natalie M Batalha²², Jacob L Bean²³, Björn Benneke^{20

21}, Zachory K Berta-Thompson²⁴, Aarynn L Carter²², Quentin Changeat^{25

26}, Knicole D Colón²⁷, Ian J M Crossfield⁸, Jean-Michel Désert⁷, Daniel Foreman-Mackey²⁸, Neale P Gibson²⁹, Laura Kreidberg¹⁹, Michael R Line³⁰, Mercedes López-Morales⁶, Karan Molaverdikhani^{31

32}, Sarah E Moran³³, Giuseppe Morello^{34

35

36}, Julianne I Moses³⁷, Sagnick Mukherjee²², Everett Schlawin³⁸, David K Sing^{12

39}, Kevin B Stevenson⁴⁰, Jake Taylor^{20

21

41}, Keshav Aggarwal⁴², Eva-Maria Ahrer^{43

44}, Natalie H Allen¹², Joanna K Barstow⁴⁵, Taylor J Bell⁴⁶, Jasmina Blecic^{47

48}, Sarah L Casewell⁴⁹, Katy L Chubb⁵⁰, Nicolas Crouzet⁵¹, Patricio E Cubillos^{52

53}, Leen Decin⁵⁴, Adina D Feinstein²³, Joanthan J Fortney²², Joseph Harrington^{55

56}, Kevin Heng^{44

57}, Nicolas Iro⁵⁸, Eliza M-R Kempton⁵⁹, James Kirk^{6

60}, Heather A Knutson¹⁷, Jessica Krick⁶¹, Jérémy Leconte⁶², Monika Lendl⁶³, Ryan J MacDonald^{13

14

64}, Luigi Mancini^{19

65

66}, Megan Mansfield³⁸, Erin M May⁴⁰, Nathan J Mayne⁶⁷, Yamila Miguel^{51

68}, Nikolay K Nikolov¹¹, Kazumasa Ohno²², Enric Palle³⁴, Vivien Parmentier^{41

69}, Dominique J M Petit Dit de la Roche⁶³, Caroline Piaulet^{20

21}, Diana Powell⁶, Benjamin V Rackham^{70

71}, Seth Redfield^{72

73}, Laura K Rogers⁷⁴, Zafar Rustamkulov¹², Xianyu Tan⁴¹, P Tremblin⁷⁵, Shang-Min Tsai⁴¹, Jake D Turner^{13

14}, Miguel de Val-Borro⁷⁶, Olivia Venot⁷⁷, Luis Welbanks³⁰, Peter J Wheatley^{43

44}, Xi Zhang⁷⁸

Affiliations

¹ School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK. lili.alderson@bristol.ac.uk.
² School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK. hannah.wakeford@bristol.ac.uk.
³ Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA.
⁴ NASA Ames Research Center, Moffett Field, CA, USA.
⁵ Department of Physics, Utah Valley University, Orem, UT, USA.
⁶ Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA, USA.
⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands.
⁸ Department of Physics & Astronomy, University of Kansas, Lawrence, KS, USA.
⁹ Astrophysics Section, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
¹⁰ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA.
¹¹ Space Telescope Science Institute, Baltimore, MD, USA.
¹² Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD, USA.
¹³ Department of Astronomy, Cornell University, Ithaca, NY, USA.
¹⁴ Carl Sagan Institute, Cornell University, Ithaca, NY, USA.
¹⁵ School of Earth and Planetary Sciences (SEPS), National Institute of Science Education and Research (NISER), Homi Bhabha National Institute (HBNI), Jatani, India.
¹⁶ School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK.
¹⁷ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
¹⁸ Center for Space and Habitability, University of Bern, Bern, Switzerland.
¹⁹ Max Planck Institute for Astronomy, Heidelberg, Germany.
²⁰ Department of Physics, Université de Montréal, Montreal, Quebec, Canada.
²¹ Institute for Research on Exoplanets, Université de Montréal, Montreal, Quebec, Canada.
²² Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA.
²³ Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
²⁴ Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO, USA.
²⁵ European Space Agency, Space Telescope Science Institute, Baltimore, MD, USA.
²⁶ Department of Physics and Astronomy, University College London, London, UK.
²⁷ NASA Goddard Space Flight Center, Greenbelt, MD, USA.
²⁸ Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA.
²⁹ School of Physics, Trinity College Dublin, Dublin, Ireland.
³⁰ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
³¹ University Observatory Munich, Ludwig Maximilian University of Munich, Munich, Germany.
³² Exzellenzcluster Origins, Garching, Germany.
³³ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
³⁴ Instituto de Astrofísica de Canarias (IAC), Tenerife, Spain.
³⁵ Departamento de Astrofísica, Universidad de La Laguna (ULL), Tenerife, Spain.
³⁶ INAF - Palermo Astronomical Observatory, Palermo, Italy.
³⁷ Space Science Institute, Boulder, CO, USA.
³⁸ Steward Observatory, University of Arizona, Tucson, AZ, USA.
³⁹ Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
⁴⁰ Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA.
⁴¹ Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK.
⁴² Indian Institute of Technology Indore, Indore, India.
⁴³ Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK.
⁴⁴ Department of Physics, University of Warwick, Coventry, UK.
⁴⁵ School of Physical Sciences, The Open University, Milton Keynes, UK.
⁴⁶ Bay Area Environmental Research Institute, NASA Ames Research Center, Moffett Field, CA, USA.
⁴⁷ Department of Physics, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
⁴⁸ Center for Astro, Particle, and Planetary Physics (CAP3), New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
⁴⁹ School of Physics and Astronomy, University of Leicester, Leicester, UK.
⁵⁰ Centre for Exoplanet Science, University of St Andrews, St Andrews, UK.
⁵¹ Leiden Observatory, University of Leiden, Leiden, The Netherlands.
⁵² INAF - Osservatorio Astrofisico di Torino, Pino Torinese, Italy.
⁵³ Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
⁵⁴ Institute of Astronomy, Department of Physics and Astronomy, KU Leuven, Leuven, Belgium.
⁵⁵ Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL, USA.
⁵⁶ Florida Space Institute, University of Central Florida, Orlando, FL, USA.
⁵⁷ Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, Munich, Germany.
⁵⁸ Institute for Astrophysics, University of Vienna, Vienna, Austria.
⁵⁹ Department of Astronomy, University of Maryland, College Park, MD, USA.
⁶⁰ Department of Physics, Imperial College London, London, UK.
⁶¹ California Institute of Technology, Pasadena, CA, USA.
⁶² Laboratoire d'Astrophysique de Bordeaux, Université de Bordeaux, Pessac, France.
⁶³ Département d'Astronomie, Université de Genève Sauverny, Versoix, Switzerland.
⁶⁴ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA.
⁶⁵ Department of Physics, University of Rome "Tor Vergata", Rome, Italy.
⁶⁶ INAF - Turin Astrophysical Observatory, Pino Torinese, Italy.
⁶⁷ Department of Physics and Astronomy, Faculty of Environment, Science and Economy, University of Exeter, Exeter, UK.
⁶⁸ SRON Netherlands Institute for Space Research, Leiden, The Netherlands.
⁶⁹ Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France.
⁷⁰ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁷¹ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁷² Astronomy Department, Wesleyan University, Middletown, CT, USA.
⁷³ Van Vleck Observatory, Wesleyan University, Middletown, CT, USA.
⁷⁴ Institute of Astronomy, University of Cambridge, Cambridge, UK.
⁷⁵ Maison de la Simulation, CEA, CNRS, Université Paris-Sud, Université Versailles St Quentin, Université Paris-Saclay, Gif-sur-Yvette, France.
⁷⁶ Planetary Science Institute, Tucson, AZ, USA.
⁷⁷ Université de Paris Cité and Université Paris-Est Creteil, CNRS, LISA, Paris, France.
⁷⁸ Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, CA, USA.

PMID: 36623549
PMCID: PMC9946835
DOI: 10.1038/s41586-022-05591-3

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec G395H

Lili Alderson et al. Nature. 2023 Feb.

. 2023 Feb;614(7949):664-669.

doi: 10.1038/s41586-022-05591-3. Epub 2023 Jan 9.

Authors

Affiliations

¹ School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK. lili.alderson@bristol.ac.uk.
² School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK. hannah.wakeford@bristol.ac.uk.
³ Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC, USA.
⁴ NASA Ames Research Center, Moffett Field, CA, USA.
⁵ Department of Physics, Utah Valley University, Orem, UT, USA.
⁶ Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA, USA.
⁷ Anton Pannekoek Institute for Astronomy, University of Amsterdam, Amsterdam, The Netherlands.
⁸ Department of Physics & Astronomy, University of Kansas, Lawrence, KS, USA.
⁹ Astrophysics Section, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
¹⁰ Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA.
¹¹ Space Telescope Science Institute, Baltimore, MD, USA.
¹² Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD, USA.
¹³ Department of Astronomy, Cornell University, Ithaca, NY, USA.
¹⁴ Carl Sagan Institute, Cornell University, Ithaca, NY, USA.
¹⁵ School of Earth and Planetary Sciences (SEPS), National Institute of Science Education and Research (NISER), Homi Bhabha National Institute (HBNI), Jatani, India.
¹⁶ School of Physics, HH Wills Physics Laboratory, University of Bristol, Bristol, UK.
¹⁷ Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
¹⁸ Center for Space and Habitability, University of Bern, Bern, Switzerland.
¹⁹ Max Planck Institute for Astronomy, Heidelberg, Germany.
²⁰ Department of Physics, Université de Montréal, Montreal, Quebec, Canada.
²¹ Institute for Research on Exoplanets, Université de Montréal, Montreal, Quebec, Canada.
²² Department of Astronomy and Astrophysics, University of California, Santa Cruz, Santa Cruz, CA, USA.
²³ Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
²⁴ Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO, USA.
²⁵ European Space Agency, Space Telescope Science Institute, Baltimore, MD, USA.
²⁶ Department of Physics and Astronomy, University College London, London, UK.
²⁷ NASA Goddard Space Flight Center, Greenbelt, MD, USA.
²⁸ Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA.
²⁹ School of Physics, Trinity College Dublin, Dublin, Ireland.
³⁰ School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
³¹ University Observatory Munich, Ludwig Maximilian University of Munich, Munich, Germany.
³² Exzellenzcluster Origins, Garching, Germany.
³³ Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.
³⁴ Instituto de Astrofísica de Canarias (IAC), Tenerife, Spain.
³⁵ Departamento de Astrofísica, Universidad de La Laguna (ULL), Tenerife, Spain.
³⁶ INAF - Palermo Astronomical Observatory, Palermo, Italy.
³⁷ Space Science Institute, Boulder, CO, USA.
³⁸ Steward Observatory, University of Arizona, Tucson, AZ, USA.
³⁹ Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
⁴⁰ Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA.
⁴¹ Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, UK.
⁴² Indian Institute of Technology Indore, Indore, India.
⁴³ Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK.
⁴⁴ Department of Physics, University of Warwick, Coventry, UK.
⁴⁵ School of Physical Sciences, The Open University, Milton Keynes, UK.
⁴⁶ Bay Area Environmental Research Institute, NASA Ames Research Center, Moffett Field, CA, USA.
⁴⁷ Department of Physics, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
⁴⁸ Center for Astro, Particle, and Planetary Physics (CAP3), New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
⁴⁹ School of Physics and Astronomy, University of Leicester, Leicester, UK.
⁵⁰ Centre for Exoplanet Science, University of St Andrews, St Andrews, UK.
⁵¹ Leiden Observatory, University of Leiden, Leiden, The Netherlands.
⁵² INAF - Osservatorio Astrofisico di Torino, Pino Torinese, Italy.
⁵³ Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
⁵⁴ Institute of Astronomy, Department of Physics and Astronomy, KU Leuven, Leuven, Belgium.
⁵⁵ Planetary Sciences Group, Department of Physics, University of Central Florida, Orlando, FL, USA.
⁵⁶ Florida Space Institute, University of Central Florida, Orlando, FL, USA.
⁵⁷ Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, Munich, Germany.
⁵⁸ Institute for Astrophysics, University of Vienna, Vienna, Austria.
⁵⁹ Department of Astronomy, University of Maryland, College Park, MD, USA.
⁶⁰ Department of Physics, Imperial College London, London, UK.
⁶¹ California Institute of Technology, Pasadena, CA, USA.
⁶² Laboratoire d'Astrophysique de Bordeaux, Université de Bordeaux, Pessac, France.
⁶³ Département d'Astronomie, Université de Genève Sauverny, Versoix, Switzerland.
⁶⁴ Department of Astronomy, University of Michigan, Ann Arbor, MI, USA.
⁶⁵ Department of Physics, University of Rome "Tor Vergata", Rome, Italy.
⁶⁶ INAF - Turin Astrophysical Observatory, Pino Torinese, Italy.
⁶⁷ Department of Physics and Astronomy, Faculty of Environment, Science and Economy, University of Exeter, Exeter, UK.
⁶⁸ SRON Netherlands Institute for Space Research, Leiden, The Netherlands.
⁶⁹ Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Nice, France.
⁷⁰ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁷¹ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA.
⁷² Astronomy Department, Wesleyan University, Middletown, CT, USA.
⁷³ Van Vleck Observatory, Wesleyan University, Middletown, CT, USA.
⁷⁴ Institute of Astronomy, University of Cambridge, Cambridge, UK.
⁷⁵ Maison de la Simulation, CEA, CNRS, Université Paris-Sud, Université Versailles St Quentin, Université Paris-Saclay, Gif-sur-Yvette, France.
⁷⁶ Planetary Science Institute, Tucson, AZ, USA.
⁷⁷ Université de Paris Cité and Université Paris-Est Creteil, CNRS, LISA, Paris, France.
⁷⁸ Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, CA, USA.

PMID: 36623549
PMCID: PMC9946835
DOI: 10.1038/s41586-022-05591-3

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^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 CO₂ (28.5σ) and H₂O (21.5σ), and identify SO₂ 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 SO₂, 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 range¹⁰.

PubMed Disclaimer

Conflict of interest statement

The authors declare no competing interests.

Figures

**Fig. 1. Light-curve precisions achieved for WASP-39b with NIRSpec G395H.**
a, Raw, uncorrected broadband light curves from the NRS1 (purple) and NRS2 (red) detectors, demonstrating the lack of dominant systematic trends in the light curves. The inset shows the drop in flux (grey-shaded region) caused by a mirror-tilt event, resulting in a distinct change in flux between NRS1 and NRS2 after the tilt event (see Extended Data Figs. 2 and 3). b, Pixel intensity map of the spectroscopic light curves after correction for the tilt event and further instrument systematics. c, Light-curve precision obtained per spectroscopic bin (black) compared with 1 and 2 times photon noise expectations (grey dashed lines) and the measured precision on the transit depth (blue). The gap between the two detectors (3.72–3.82 μm) is highlighted in the middle and bottom plots. All data shown are from fitting pipeline 1 (see Methods).

**Fig. 2. WASP-39b transmission spectra measured at 10-pixel resolution (≈7-nm-wide bins, R ≈ 600) using several fitting pipelines.**
We show the resultant spectra from five out of 11 independent fitting pipelines, which used distinct analysis methods to demonstrate the robust structure of the spectrum (see Methods for details on each fitting pipeline and comparative statistics). The black points show the weighted-average transmission spectrum computed from the transit depth values in each bin weighted by 1/σ², in which σ is the uncertainty on the data point from each of the 11 fitting pipelines. The error bars were computed from the unweighted mean uncertainty in each bin (see Extended Data Fig. 5). All spectra show consistent broadband absorption short of 3.7 μm, around 4.1 μm and from 4.2 to 4.5 μm.

**Fig. 3. Spectra from three independent 1D RCTE models and their residuals, fit to the weighted-average WASP-39b G395H transmission spectrum.**
a, Spectra from the three models. b, Their residuals. The models are dominated by absorption from H₂O and CO₂ with a grey-cloud-top pressure corresponding to ≈1 mbar. The models find that the data are best explained by 3–10 times solar metallicity (M/H) and sub-solar to solar C/O (C/O = 0.30–0.46). The extra absorption owing to SO₂, seen in the spectrum around 4.1 μm, is not included in the RCTE model grids and causes a marked impact on the χ²/N (see Fig. 4).

**Fig. 4. Contribution of opacity sources to the best-fitting model with injected SO₂.**
a, The lowest χ²/N best-fitting model (PICASO in Fig. 3) with an injected abundance of 10^−5.6 (VMR) SO₂. We also show this model with a selection of the anticipated absorbing species and the cloud opacity removed to indicate their contributions to the model. The inclusion of SO₂ in the model decreases the χ²/N from 1.08 (shown in Fig. 3) to 1.02, resulting in a 4.8σ detection (see Extended Data Table 3). b–e, The effect of removing the corresponding molecular opacity from the spectrum (shaded region). Our best-fit model is also affected by minor opacities from CO, H₂S, OCS and CH₄, although their spectral features cannot be robustly detected in the spectrum. We show a model without CO and CH₄ in a to demonstrate this, with the minor contribution by CO also highlighted in e.

**Extended Data Fig. 1. The throughput and spectral trace for WASP-39 across NRS1 and NRS2.**
a, Normalized throughput of NRS1 and NRS2 detectors (as custom produced; see Methods, ‘Limb-darkening’), which shows the cutoff at short wavelengths. b, 2D spectral images of the trace produced from the ExoTiC-JEDI [V1] reduction before cleaning steps. The aspect ratio has been stretched in the y direction to show the structure of the trace over the 32-pixel-wide subarray more clearly. The NRS2 spectral position is slightly offset from that of NRS1, as the NRS2 subarray was moved following commissioning to ensure that the centre of the spectral trace fell fully on the detector and did not fall off the top-right corner.

**Extended Data Fig. 2. Time-dependent decorrelation parameters.**
a, The change in the FWHM of the spectral trace at selected wavelengths. This change does not correspond to any high-gain antenna movements and is attributed to a large mirror-tilt event. These measurements demonstrate that the mirror-tilt event has a wavelength dependence. Changes to the PSF have a larger impact at short wavelengths, as the PSF of the spectrum increases with wavelength. b,c, The change in the x-pixel and y-pixel position of the spectral trace as functions of time, respectively. Positional shifts are calculated by cross-correlating the spectral trace with a template to measure sub-pixel movement on the detector. The y-position shift clearly shows a link to the mirror-tilt event.

**Extended Data Fig. 3. Normalized flux offset of the stellar baseline before and after the tilt event as a function of wavelength for NRS1 and NRS2.**
Purple denotes NRS1 and orange denotes NRS2. The normalized flux offset is calculated per pixel by measuring the median flux in the stellar baseline before and after the transit and calculating the difference. These differences are then normalized by the before-transit flux and plotted on a common scale. Overplotted are the data binned to a resolution of 10 pixels to match our presented transmission spectra (Fig. 2). We also show a linear fit to each detector to better quantify the decreasing tilt flux amplitude with increasing wavelength (NRS1 = −0.00073374x + 0.00707344, NRS2 = −0.00067165x + 0.00588128).

**Extended Data Fig. 4. Normalized root-mean-squared binning statistic for three of the 11 reductions detailed in Methods.**
In each subplot, the red line shows the expected relationship for perfect Gaussian white noise. The black lines show the observed noise from each spectroscopic light curve for pipelines 1, 3 and 5. To compare bins and noise levels, values for all bins in each pipeline are normalized by dividing by the value for a bin width of 1.

**Extended Data Fig. 5. Comparison between all fitting pipelines performed on the spectroscopic light curves.**
a, The underlying grey data points show the standard deviation between all transmission spectra per spectral bin. The black line shows the unweighted mean uncertainty on the transit depth per bin. Spikes in the uncertainties correspond to spectral bins with higher standard deviations, probably because of differences in pixel-flagging or sigma-clipping at the light-curve level. b, Gaussian PDFs of the normalized transmission spectrum residuals, showing the mean offset and the spread relative to the weighted-average transmission spectrum. c, Histograms of the normalized transmission spectrum residuals aligned to zero by subtracting the mean of the distribution that was used to generate the PDF above. In panels b and c, the coloured lines and numbers correspond to the fitting pipeline used to obtain each transmission spectrum, as summarized in Extended Data Table 1. The dashed lines correspond to the fitting pipeline results presented in Fig. 2, demonstrating that they are drawn from across the distribution.

**Extended Data Fig. 6. Gaussian versus flat-line fits to the residual transmission spectrum for CO₂, H₂O, SO₂ and the 4.56-μm feature.**
Shown after all other absorption from the best-fit model is subtracted from the data. Each of the Gaussian fits has a higher Bayesian evidence than the flat-line fits, indicating a detection, although to varying degrees of significance.

**Extended Data Fig. 7. Model transmission spectra of WASP-39b with PHOENIX and gCMCRT with varying abundances of SO₂.**
Model transmission spectra compared with the observed spectral feature at 4.1 μm in the G395H data. At wavelengths short of 3.95 μm, which is outside the SO₂ band, all models overlap, further suggesting that the data can be explained by the presence of SO₂ in the atmosphere. By interpolating these 10 times solar metallicity models, we find a best-fit SO₂ abundance of 4.6 ± 0.67 ppm. With the best-fit PICASO 3.0 at 3 times solar metallicity, we find an SO₂ abundance of 2.5 ± 0.65 ppm.

See this image and copyright information in PMC

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.

References

1. Öberg KI, Murray-Clay R, Bergin EA. The effects of snowlines on C/O in planetary atmospheres. Astrophys. J. Lett. 2011;743:L16. doi: 10.1088/2041-8205/743/1/L16. - DOI
1. Mordasini C, van Boekel R, Mollière P, Henning T, Benneke B. The imprint of exoplanet formation history on observable present-day spectra of hot Jupiters. Astrophys. J. 2016;832:41. doi: 10.3847/0004-637X/832/1/41. - DOI
1. Sing DK, et al. A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion. Nature. 2016;529:59–62. doi: 10.1038/nature16068. - DOI - PubMed
1. Wakeford HR, et al. The complete transmission spectrum of WASP-39b with a precise water constraint. Astron. J. 2018;155:29. doi: 10.3847/1538-3881/aa9e4e. - DOI
1. Alam MK, et al. The Hubble Space Telescope PanCET program: an optical to infrared transmission spectrum of HAT-P-32Ab. Astron. J. 2020;160:51. doi: 10.3847/1538-3881/ab96cb. - DOI

Save citation to file

Email citation

Add to Collections

Add to My Bibliography

Your saved search

Create a file for external citation management software

Your RSS Feed

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec G395H

Affiliations

Early Release Science of the exoplanet WASP-39b with JWST NIRSpec G395H

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

Comment in

References

Publication types

Grants and funding

LinkOut - more resources

Full Text Sources