Hydrogen sulfide and metal-enriched atmosphere for a Jupiter-mass exoplanet

Creators: Fu, Guangwei¹; Welbanks, Luis²; Deming, Drake³; Inglis, Julie⁴; Zhang, Michael⁵; Lothringer, Joshua⁶; Ih, Jegug³; Moses, Julianne I.⁷; Schlawin, Everett⁸; Knutson, Heather A,⁴; Henry, Gregory⁹; Greene, Thomas¹⁰; Sing, David K.¹; Savel, Arjun B.³; Kempton, Eliza M.-R.³; Louie, Dana R.¹¹; Line, Michael²; Nixon, Matt³

1. Johns Hopkins University
2. Arizona State University
3. University of Maryland, College Park
4. California Institute of Technology
5. University of Chicago
6. Utah Valley University
7. Space Science Institute
8. Steward Observatory
9. Tennessee State University
10. Ames Research Center
11. Goddard Space Flight Center

Abstract

As the closest transiting hot Jupiter to Earth, HD 189733b has been the benchmark planet for atmospheric characterization. It has also been the anchor point for much of our theoretical understanding of exoplanet atmospheres from composition, chemistry, aerosols to atmospheric dynamics, escape and modelling techniques. Previous studies of HD 189733b have detected carbon and oxygen-bearing molecules H₂O and CO (refs. 12-13) in the atmosphere. The presence of CO₂ and CH₄ has been claimed but later disputed. The inferred metallicity based on these measurements, a key parameter in tracing planet formation locations, varies from depletion to enhancement, hindered by limited wavelength coverage and precision of the observations. Here we report detections of H₂O (13.4σ), CO₂ (11.2σ), CO (5σ) and H₂S (4.5σ) in the transmission spectrum (2.4–5.0 μm) of HD 189733b. With an equilibrium temperature of about 1,200 K, H₂O, CO and H₂S 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.

Copyright and License

Acknowledgement

G.F. acknowledges support for this work provided by NASA through JWST GO program funding support.

Data Availability

The NIRCam data used in this paper are from JWST GO program 1633 (principal investigator D.D.) and are publicly available from the Mikulski Archive for Space Telescopes (MAST; https://mast.stsci.edu). White-light transit lightcurve, transit spectrum and models are archived at Zenodo (https://zenodo.org/records/11459715) (ref. ⁹⁹).

Code Availability

We used the following codes to reduce JWST NIRCam data: STScI JWST Calibration pipeline, Eureka!⁵⁷, numpy¹⁰⁰, scipy⁹⁰ and matplotlib¹⁰¹.

Contributions

G.F. led the data analysis effort, contributed to the interpretation of the observations and led the writing of the paper. L.W. led the modelling analysis effort, including the grid and free retrievals using 1D-RCPE models. D.D. led the JWST GO 1633 program proposal and contributed to the data analysis effort. J.Inglis., M.Z. and E.S. contributed to the data analysis effort by providing additional data reductions for both NIRCam F322W2 and F444W wavelength channels. J.L., J.Ih and M.N. performed 1D forward models and retrievals. J.I.M. performed photochemistry calculations. D.K.S. helped with creating the figures and text in the paper. M.L. and E.M.-R.K. contributed to the model interpretation efforts. H.A.K., T.G., A.B.S. and D.R.L. are part of the proposal team and provided useful feedback for the project and the paper. G.H. provided the ground-based photometric monitoring data.

Conflict of Interest

The authors declare no competing interests.

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