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An extended low-density atmosphere around the Jupiter-sized planet WASP-193 b

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Abstract

Gas giants transiting bright nearby stars provide crucial insights into planetary system formation and evolution mechanisms. Most of these planets show certain average characteristics, serving as benchmarks for our understanding of planetary systems. However, outliers like the planet we present in this study, WASP-193 b, offer unique opportunities to explore unconventional formation and evolution processes. This planet completes an orbit around its V-band-magnitude 12.2 F9 main-sequence host star every 6.25 days. Our analyses found that WASP-193 b has a mass of 0.139 ± 0.029 MJ and a radius of 1.464 ± 0.058 RJ, translating into an extremely low density of 0.059 ± 0.014g cm−3, at least one order of magnitude less than standard gas giants like Jupiter. Typical gas giants such as Jupiter have densities that range between 0.2 g cm−3 and 2 g cm−3. The combination of its large transit depth (1.4%), extremely low density, high-equilibrium temperature (1,254 ± 31 K) and the infrared brightness of its host star (K-band magnitude 10.7) makes WASP-193 b an exquisite target for characterization by transmission spectroscopy (transmission spectroscopy metric ~600). One single JWST transit observation would yield detailed insights into its atmospheric properties and planetary mass, providing a unique window to explore the mechanisms behind its exceptionally low density and shed light on giant planets’ diverse nature.

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Fig. 1: Photometric and spectroscopic follow-up.
Fig. 2: Planetary diagrams of known transiting exoplanets with radius and mass precisions better than 8% and 25%, respectively.
Fig. 3: Planetary radius as a function of age for two evolution models.
Fig. 4: Feasibility of WASP-193 b for transmission spectroscopy studies.
Fig. 5: WASP-193 b as an exquisite target for atmospheric characterization.

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Data availability

The TRAPPIST-South and SPECULOOS-South data analysed are available at CDS via anonymous ftp at http://cdsarc.u-strasbg.fr/ (130.79.128.5). The HARPS and CORALIE data analysed are available in the European Southern Observatory archive (ESO; http://archive.eso.org/cms.html) The TESS data analysed are available in the Mikulski Archive for Space Telescopes (MAST; https://archive.stsci.edu/). Source data are provided with this paper.

Code availability

The Prose and MCMC codes used for this paper are publicly available.

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Acknowledgements

WASP-South is hosted by the South African Astronomical Observatory and we are grateful for their ongoing support and assistance. Funding for WASP comes from consortium universities and from the UK’s Science and Technology Facilities Council. The research leading to these results has received funding from the European Research Council (ERC) under the FP/2007–2013 ERC grant agreement no. 336480, and under the H2020 ERC grant agreement no. 679030; and from an Actions de Recherche Concertée (ARC) grant, financed by the Wallonia-Brussels Federation. The Euler Swiss telescope by the Swiss National Science Foundation (SNF). This work has been carried out in part within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation. This study is based on observations collected at the European Southern Observatory under ESO programme 0102.C-0414, principal investigator L.D.N. TRAPPIST-South is funded by the Belgian National Fund for Scientific Research (F.R.S.-FNRS) under grant PDR T.0120.21, with the participation of the Swiss National Science Fundation (SNF). M.G. is F.R.S.-FNRS Research Director and E.J. is F.R.S.-FNRS Senior Research Associate. V.V.G. is an F.R.S.-FNRS Research Associate. The postdoctoral fellowship of K.B. is funded by F.R.S.-FNRS grant T.0109.20 and by the Francqui Foundation. This publication benefits from the support of the French Community of Belgium in the context of the FRIA Doctoral Grant awarded to M.T. The ULiege’s contribution to SPECULOOS has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) (grant agreement no. 336480/SPECULOOS), from the Balzan Prize Foundation, from the Belgian Scientific Research Foundation (F.R.S.-FNRS; grant no. T.0109.20), from the University of Liege, and from the ARC grant for Concerted Research Actions financed by the Wallonia-Brussels Federation. This work is supported by a grant from the Simons Foundation (principal investigator D.Q., grant number 327127). J.d.W. and MIT gratefully acknowledge financial support from the Heising-Simons Foundation, Mrs. C. Masson, Masson and P. A. Gilman for Artemis, the first telescope of the SPECULOOS network situated in Tenerife, Spain. This work is supported by the Swiss National Science Foundation (PP00P2-163967, PP00P2-190080 and the National Centre for Competence in Research PlanetS). This work has received fund from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 803193/BEBOP), from the MERAC foundation, and from the Science and Technology Facilities Council (STFC; grant no. ST/S00193X/1). C.D. was supported by the Swiss National Science Foundation (SNSF) under grant PZ00P2_174028. M.L. acknowledges support of the Swiss National Science Foundation under grant number PCEFP2_194576. E.D. is a Paris Region Fellow and acknowledges support from the innovation and research Horizon 2020 programme in the context of the Marie Sklodowska-Curie subvention 945298. F.J.P. acknowledges financial support from the grant CEX2021-001131-S funded by MCIN/AEI/ 10.13039/501100011033 and through projects PID2019-109522GB-C52 and PID2022-137241NB-C43.

Author information

Authors and Affiliations

  1. Astrobiology Research Unit, Université de Liège, Liège, Belgium

    Khalid Barkaoui, Francisco J. Pozuelos, Michaël Gillon, Mourad Ghachoui, Laetitia Delrez, Lionel Garcia & Mathilde Timmermans

  2. Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Faculty of sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco

    Khalid Barkaoui, Abderahmane Soubkiou, Mourad Ghachoui, Zouhair Benkhaldoun & Abdelhadi Jabiri

  3. Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, MA, USA

    Khalid Barkaoui, Prajwal Niraula, Julien de Wit & Artem Burdanov

  4. Instituto de Astrofísica de Canarias (IAC), La Laguna, Spain

    Khalid Barkaoui

  5. Instituto de Astrofísica de Andalucía (IAA-CSIC), Granada, Spain

    Francisco J. Pozuelos

  6. Astrophysics Group, Keele University, Staffordshire, UK

    Coel Hellier, Barry Smalley & Pierre F. L. Maxted

  7. Observatoire de Genève, Université de Genève, Sauverny, Switzerland

    Louise D. Nielsen, Francois Bouchy, Monika Lendl, Didier Queloz, Oliver Turner & Stephane Udry

  8. European Southern Observatory, Garching bei München, Germany

    Louise D. Nielsen

  9. Department of Astrophysics, University of Zürich, Zurich, Switzerland

    Simon Müller, Caroline Dorn & Ravit Helled

  10. Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Liège, Belgium

    Emmanuel Jehin, Valerie Van Grootel & Laetitia Delrez

  11. Center for Space and Habitability, University of Bern, Bern, Switzerland

    Brice-Olivier Demory

  12. Instituto de Astrofisica e Ciencias do Espaco, Universidade do porto, CAUP, Porto, Portugal

    Abderahmane Soubkiou

  13. Department of Physics, University of Warwick, Coventry, UK

    David. R. Anderson & Richard G. West

  14. LESIA, Observatoire de Paris, CNRS, Université Paris Diderot, Université Pierre et Marie Curie, Paris, France

    Elsa Ducrot

  15. Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, Paris, France

    Elsa Ducrot

  16. Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA

    Lionel Garcia

  17. Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, CO, USA

    Catriona A. Murray

  18. Cavendish Laboratory, Cambridge, UK

    Peter Pihlmann Pedersen & Didier Queloz

  19. School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, UK

    Daniel Sebastian & Amaury H. M. J. Triaud

  20. Space Forge, Cardiff, UK

    Oliver Turner

  21. Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK

    Richard G. West

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Contributions

K.B. led the project and performed and interpreted the global analyses with support from F.J.P. and M. Gillon. F.J.P. led the interpretation of the results and writing of the paper. P.N. and J.d.W. performed the assessment of atmospheric characterization suitability. C.H., O.T., D.R.A., S.U. and R.G.W. performed the WASP-South observation and data reduction. C.D., R.H. and S.M. performed planet interior models and interpretation of the results. B.S., V.V.G., P.F.L.M., A.S. and M. Ghachoui performed spectroscopic data, stellar evolutionary models and SED analysis. L.D.N., F.B. and M.L. performed radial velocity measurements. E.J., E.D., C.A.M. and P.P.P. performed photometric follow-ups using TRAPPIST-South and SPECULOOS-South facilities and data reduction using Prose. All co-authors read and commented on the paper and helped with its revision.

Corresponding authors

Correspondence to Khalid Barkaoui or Francisco J. Pozuelos.

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Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks Thomas Wilson and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–5 and Tables 1–5.

Supplementary Data

WASP-South photometric data.

Source data

Source Data Fig. 1

Space and ground-based photometry and RVs.

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Barkaoui, K., Pozuelos, F.J., Hellier, C. et al. An extended low-density atmosphere around the Jupiter-sized planet WASP-193 b. Nat Astron (2024). https://doi.org/10.1038/s41550-024-02259-y

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