High atmospheric metal enrichment for a Saturn-mass planet

Jacob L Bean¹, Qiao Xue^{2

3}, Prune C August^{2

4}, Jonathan Lunine⁵, Michael Zhang², Daniel Thorngren⁶, Shang-Min Tsai^{7

8}, Keivan G Stassun⁹, Everett Schlawin¹⁰, Eva-Maria Ahrer¹¹, Jegug Ih¹², Megan Mansfield¹⁰

Affiliations

¹ Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA. jbean@astro.uchicago.edu.
² Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
³ School of Physics and Astronomy, Shanghai Jiaotong University, Shanghai, China.
⁴ Institute of Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
⁵ Department of Astronomy, Cornell University, Ithaca, NY, USA.
⁶ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA.
⁷ Department of Earth Sciences, University of California, Riverside, CA, USA.
⁸ Department of Physics, University of Oxford, Oxford, UK.
⁹ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA.
¹⁰ Steward Observatory, University of Arizona, Tucson, AZ, USA.
¹¹ Department of Physics, University of Warwick, Coventry, UK.
¹² Department of Astronomy, University of Maryland, College Park, MD, USA.

PMID: 36972686
DOI: 10.1038/s41586-023-05984-y

High atmospheric metal enrichment for a Saturn-mass planet

Jacob L Bean et al. Nature. 2023 Jun.

. 2023 Jun;618(7963):43-46.

doi: 10.1038/s41586-023-05984-y. Epub 2023 Mar 27.

Authors

Affiliations

¹ Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA. jbean@astro.uchicago.edu.
² Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL, USA.
³ School of Physics and Astronomy, Shanghai Jiaotong University, Shanghai, China.
⁴ Institute of Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
⁵ Department of Astronomy, Cornell University, Ithaca, NY, USA.
⁶ Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD, USA.
⁷ Department of Earth Sciences, University of California, Riverside, CA, USA.
⁸ Department of Physics, University of Oxford, Oxford, UK.
⁹ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, USA.
¹⁰ Steward Observatory, University of Arizona, Tucson, AZ, USA.
¹¹ Department of Physics, University of Warwick, Coventry, UK.
¹² Department of Astronomy, University of Maryland, College Park, MD, USA.

PMID: 36972686
DOI: 10.1038/s41586-023-05984-y

Abstract

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 metallicity⁴. 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 solar¹⁰ at more than 4σ confidence. This result is based on modelling CO₂ and H₂O 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.

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References

1. Pollack, J. B. et al. Formation of the giant planets by concurrent accretion of solids and gas. Icarus 124, 62 (1996). - DOI
1. Fortney, J. J. et al. A framework for characterizing the atmospheres of low-mass low-density transiting planets. Astrophys. J. 775, 80 (2013). - DOI
1. Venturini, J., Alibert, Y. & Benz, W. Planet formation with envelope enrichment: new insights on planetary diversity. Astron. Astrophys. 596, A90 (2016). - DOI
1. Thorngren, D. P., Fortney, J. J., Murray-Clay, R. A. & Lopez, E. D. The mass-metallicity relation for giant planets. Astrophys. J. 831, 64 (2016). - DOI
1. Sato, B. et al. The N2K Consortium. II. A transiting hot Saturn around HD 149026 with a large dense core. Astrophys. J. 633, 465 (2005). - DOI

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High atmospheric metal enrichment for a Saturn-mass planet

Affiliations

High atmospheric metal enrichment for a Saturn-mass planet

Authors

Affiliations

Abstract

References