CaltechAUTHORS
Published August 10, 2023 | Version Published + Supplemental Material
Journal Article Open

A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b

Creators

  • 1. ROR icon University of Montreal
  • 2. ROR icon University of Michigan–Ann Arbor
  • 3. ROR icon Carnegie Institution for Science
  • 4. ROR icon Arizona State University
  • 5. ROR icon University of Arizona
  • 6. ROR icon Cornell University
  • 7. ROR icon University of Chicago
  • 8. ROR icon University of Maryland, College Park
  • 9. ROR icon Space Telescope Science Institute
  • 10. ROR icon Observatoire de la Côte d'Azur
  • 11. ROR icon Goddard Space Flight Center
  • 12. ROR icon Shanghai Jiao Tong University
  • 13. ROR icon University of Oxford
  • 14. ROR icon University of Exeter
  • 15. ROR icon University of Bern
  • 16. ROR icon University of Amsterdam
  • 17. ROR icon University of Kansas
  • 18. ROR icon Massachusetts Institute of Technology
  • 19. ROR icon University of Bristol
  • 20. ROR icon University of California, Santa Cruz
  • 21. ROR icon University of Colorado Boulder
  • 22. ROR icon University College London
  • 23. ROR icon National Institute of Science Education and Research
  • 24. ROR icon University of Central Florida
  • 25. ROR icon California Institute of Technology
  • 26. ROR icon Max Planck Institute for Astronomy
  • 27. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 28. ROR icon Johns Hopkins University
  • 29. ROR icon Johns Hopkins University Applied Physics Laboratory
  • 30. ROR icon Indian Institute of Technology Indore
  • 31. ROR icon University of Warwick
  • 32. ROR icon Bay Area Environmental Research Institute
  • 33. ROR icon New York University Abu Dhabi
  • 34. ROR icon Andrés Bello University
  • 35. ROR icon Millenium Nucleus for Planet Formation
  • 36. ROR icon Centro de Astrofísica y Tecnologías Afines
  • 37. ROR icon University of Leicester
  • 38. ROR icon Leiden University
  • 39. ROR icon Osservatorio Astrofisico di Torino
  • 40. ROR icon Space Research Institute
  • 41. ROR icon KU Leuven
  • 42. ROR icon Trinity College Dublin
  • 43. ROR icon Ludwig-Maximilians-Universität München
  • 44. ROR icon German Aerospace Center
  • 45. ROR icon University of Paris
  • 46. ROR icon Laboratory of Astrophysics of Bordeaux
  • 47. ROR icon University of Geneva
  • 48. ROR icon Utah Valley University
  • 49. ROR icon University of Rome Tor Vergata
  • 50. ROR icon Excellence Cluster Origins
  • 51. ROR icon Instituto de Astrofísica de Canarias
  • 52. ROR icon Wesleyan University
  • 53. ROR icon University of California, Riverside
  • 54. ROR icon French National Centre for Scientific Research

Abstract

Close-in giant exoplanets with temperatures greater than 2,000 K ('ultra-hot Jupiters') have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the Hubble Space Telescope (HST) and Spitzer Space Telescope. However, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis. Here we present a dayside thermal emission spectrum of the ultra-hot Jupiter WASP-18b obtained with the NIRISS13 instrument on the JWST. The data span 0.85 to 2.85 μm in wavelength at an average resolving power of 400 and exhibit minimal systematics. The spectrum shows three water emission features (at >6σ confidence) and evidence for optical opacity, possibly attributable to H−, TiO and VO (combined significance of 3.8σ). Models that fit the data require a thermal inversion, molecular dissociation as predicted by chemical equilibrium, a solar heavy-element abundance ('metallicity', M/H = 1.03^(+1.11)_(−0.51) times solar) and a carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside brightness temperature map, which shows a peak in temperature near the substellar point that decreases steeply and symmetrically with longitude towards the terminators.

Additional Information

© The Author(s) 2023. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. This work is based on observations made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127. These observations are associated with program JWST-ERS-01366. Support for this program was provided by NASA through a grant from the Space Telescope Science Institute. The results reported herein benefited during the design phase from collaborations and/or information exchange within NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. L.-P.C. acknowledges funding by the Technologies for Exo-Planetary Science (TEPS) Natural Sciences and Engineering Research Council of Canada (NSERC) CREATE Trainee Program. M.M., R.J.M. and L.W. acknowledge support provided by NASA through the NASA Hubble Fellowship Program. A.D.F. acknowledges support from the National Science Foundation through the Graduate Research Fellowship Program. I.W. acknowledges support provided by NASA through the NASA Postdoctoral Program. B.V.R. acknowledges support from the 51 Pegasi b Fellowship funded by the Heising-Simons Foundation. Contributions. All authors played a notable role in one or more of the following: development of the original proposal, management of the project, definition of the target list and observation plan, analysis of the data, theoretical modelling and preparation of this manuscript. Some specific contributions are listed as follows. N.M.B., J.L.B. and K.B.S. provided overall program leadership and management. L.-P.C. and B.B. led the efforts for this manuscript. D.K.S., E.M.-R.K., H.A.K., H.R.W., I.J.M.C., J.L.B., J.-M.D., K.B.S., L.K., M.L.-M., M.R.L., N.M.B., N.C., V.P. and Z.K.B.-T. made substantial contributions to the design of the program. K.B.S. generated the observing plan, with input from the team. N.E. provided instrument expertise. B.B., E.M.-R.K., H.R.W., I.J.M.C., J.L.B., L.K., M.L.-M., M.R.L., N.M.B. and Z.K.B.-T. led or co-led working groups and/or contributed to substantial strategic planning efforts, such as the design and implementation of the pre-launch Data Challenges. A.L.C., D.K.S., N.E., N.P.G. and V.P. generated simulated data for pre-launch testing of methods. B.B., E.R., J.L.B., L.-P.C., T.D.K. and V.P. contributed notably to the writing of this manuscript, along with contributions in the Methods from A.A.A.P., A.B.S., A.D.F., H.B., I.W., L.A.D.S., L.S.W., M.M., M.R., R.C., R.J.M. and X.T. A.D.F., L.A.D.S., L.-P.C. and M.R. contributed to the development of data-analysis pipelines and/or provided the data-analysis products used in this analysis, that is, reduced the data, modelled the light curves and/or produced the planetary spectrum. I.W. performed the revised TESS analysis. A.A.A.P., L.-P.C., L.S.W. and R.J.M. performed atmospheric retrievals on the planetary spectrum. M.H., M.M., N.T.L. and R.C. performed the secondary-eclipse-mapping analysis. E.K.H.L., H.B., L.-P.C., R.C., V.P. and X.T. provided GCM and/or post-processed GCM results used in this analysis. A.B.S. generated the disequilibrium chemistry models. H.S. and L.-P.C. produced the absolute flux-calibrated stellar spectrum and performed the comparison with stellar models. L.-P.C., L.S.W. and R.C. generated the figures for this manuscript. B.V.R., H.R.W., I.J.M.C., J.H., L.W., M.C.N. and X.Z. provided substantial feedback to the manuscript and/or coordinated comments from all other authors. A.S., C.C., C.P., E.-M.A., E.P., J.B., J.J.F., J.M.G., J.L., J.D.L., K.A., K.H., K.M., K.O., L.D., L.M., M.K.A., M.L., N.I., N.K.N., O.V., P.E.C., P.-O.L., P.-A.R., P.J.W., Q.C., S.L.C., S.K., S.R., S.-M.T., T.J.B., T.H. and T.M.-E. provided scientific and technical input to the manuscript. Data availability. The data used in this work are publicly available in the Mikulski Archive for Space Telescopes (MAST) (https://archive.stsci.edu/). The data that were used to create all of the figures in this manuscript are freely available on Zenodo (https://doi.org/10.5281/zenodo.7907569). All further data are available on request. Source data are provided with this paper. Code availability. The open-source pipelines that were used throughout this work are as follows: NIRISS/SOSS data reduction: nirHiss (https://github.com/afeinstein20/nirhiss); supreme-SPOON (https://github.com/radicamc/supreme-spoon); transitspectroscopy (https://github.com/nespinoza/transitspectroscopy). Light-curve fitting: batman (https://github.com/lkreidberg/batman); emcee (https://emcee.readthedocs.io/en/stable/). Atmospheric retrievals: CHIMERA (https://github.com/mrline/CHIMERA); POSEIDON (https://github.com/MartianColonist/POSEIDON); MultiNest (https://github.com/JohannesBuchner/MultiNest); PyMultiNest (https://github.com/JohannesBuchner/PyMultiNest). Eclipse mapping: ThERESA (https://github.com/rychallener/ThERESA); Eigenspectra (https://github.com/multidworlds/eigenspectra). Atmospheric modelling: HELIOS (https://github.com/exoclime/HELIOS); HELIOS-K (https://github.com/exoclime/HELIOS-K); PLATON (https://github.com/ideasrule/platon); VULCAN (https://github.com/exoclime/VULCAN). The authors declare no competing interests.

Attached Files

Published - s41586-023-06230-1.pdf

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Additional details

Identifiers

PMCID
PMC10412449
Eprint ID
122457
Resolver ID
CaltechAUTHORS:20230725-856943000.25

Related works

Describes
10.5281/zenodo.7907569 (DOI)

Funding

NASA
NAS 5-03127
NASA
JWST-ERS-01366
Natural Sciences and Engineering Research Council of Canada (NSERC)
NASA Hubble Fellowship
NSF Graduate Research Fellowship
NASA Postdoctoral Program
Heising-Simons Foundation
51 Pegasi b Fellowship

Dates

Created
2023-08-18
Created from EPrint's datestamp field
Updated
2023-08-18
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
Division of Geological and Planetary Sciences (GPS)