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

Louis-Philippe Coulombe (), Björn Benneke, Ryan Challener, Anjali A. A. Piette, Lindsey S. Wiser, Megan Mansfield, Ryan J. MacDonald, Hayley Beltz, Adina D. Feinstein, Michael Radica, Arjun B. Savel, Leonardo A. Santos, Jacob L. Bean, Vivien Parmentier, Ian Wong, Emily Rauscher, Thaddeus D. Komacek, Eliza M.-R. Kempton, Xianyu Tan, Mark Hammond, Neil T. Lewis, Michael R. Line, Elspeth K. H. Lee, Hinna Shivkumar, Ian J. M. Crossfield, Matthew C. Nixon, Benjamin V. Rackham, Hannah R. Wakeford, Luis Welbanks, Xi Zhang, Natalie M. Batalha, Zachory K. Berta-Thompson, Quentin Changeat, Jean-Michel Désert, Néstor Espinoza, Jayesh M. Goyal, Joseph Harrington, Heather A. Knutson, Laura Kreidberg, Mercedes López-Morales, Avi Shporer, David K. Sing, Kevin B. Stevenson, Keshav Aggarwal, Eva-Maria Ahrer, Munazza K. Alam, Taylor J. Bell, Jasmina Blecic, Claudio Caceres, Aarynn L. Carter, Sarah L. Casewell, Nicolas Crouzet, Patricio E. Cubillos, Leen Decin, Jonathan J. Fortney, Neale P. Gibson, Kevin Heng, Thomas Henning, Nicolas Iro, Sarah Kendrew, Pierre-Olivier Lagage, Jérémy Leconte, Monika Lendl, Joshua D. Lothringer, Luigi Mancini, Thomas Mikal-Evans, Karan Molaverdikhani, Nikolay K. Nikolov, Kazumasa Ohno, Enric Palle, Caroline Piaulet, Seth Redfield, Pierre-Alexis Roy, Shang-Min Tsai, Olivia Venot and Peter J. Wheatley
Additional contact information
Louis-Philippe Coulombe: Université de Montréal
Björn Benneke: Université de Montréal
Ryan Challener: University of Michigan
Anjali A. A. Piette: Carnegie Institution for Science
Lindsey S. Wiser: Arizona State University
Megan Mansfield: University of Arizona
Ryan J. MacDonald: University of Michigan
Hayley Beltz: University of Michigan
Adina D. Feinstein: University of Chicago
Michael Radica: Université de Montréal
Arjun B. Savel: University of Maryland
Leonardo A. Santos: Space Telescope Science Institute
Jacob L. Bean: University of Chicago
Vivien Parmentier: Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange
Ian Wong: NASA Goddard Space Flight Center
Emily Rauscher: University of Michigan
Thaddeus D. Komacek: University of Maryland
Eliza M.-R. Kempton: University of Maryland
Xianyu Tan: Shanghai Jiao Tong University
Mark Hammond: University of Oxford
Neil T. Lewis: University of Exeter
Michael R. Line: Arizona State University
Elspeth K. H. Lee: University of Bern
Hinna Shivkumar: University of Amsterdam
Ian J. M. Crossfield: University of Kansas
Matthew C. Nixon: University of Maryland
Benjamin V. Rackham: Massachusetts Institute of Technology
Hannah R. Wakeford: University of Bristol
Luis Welbanks: Arizona State University
Xi Zhang: University of California, Santa Cruz
Natalie M. Batalha: University of California, Santa Cruz
Zachory K. Berta-Thompson: University of Colorado Boulder
Quentin Changeat: Space Telescope Science Institute
Jean-Michel Désert: University of Amsterdam
Néstor Espinoza: Space Telescope Science Institute
Jayesh M. Goyal: National Institute of Science Education and Research (NISER), Homi Bhabha National Institute (HBNI)
Joseph Harrington: University of Central Florida
Heather A. Knutson: California Institute of Technology
Laura Kreidberg: Max Planck Institute for Astronomy
Mercedes López-Morales: Center for Astrophysics | Harvard & Smithsonian
Avi Shporer: Massachusetts Institute of Technology
David K. Sing: Johns Hopkins University
Kevin B. Stevenson: Johns Hopkins Applied Physics Laboratory
Keshav Aggarwal: Indian Institute of Technology
Eva-Maria Ahrer: University of Warwick
Munazza K. Alam: Carnegie Institution for Science
Taylor J. Bell: Bay Area Environmental Research Institute, NASA Ames Research Center
Jasmina Blecic: New York University Abu Dhabi
Claudio Caceres: Universidad Andrés Bello
Aarynn L. Carter: University of California, Santa Cruz
Sarah L. Casewell: University of Leicester
Nicolas Crouzet: University of Leiden
Patricio E. Cubillos: INAF – Osservatorio Astrofisico di Torino
Leen Decin: KU Leuven
Jonathan J. Fortney: University of California, Santa Cruz
Neale P. Gibson: Trinity College Dublin
Kevin Heng: University of Warwick
Thomas Henning: Max Planck Institute for Astronomy
Nicolas Iro: German Aerospace Center (DLR)
Sarah Kendrew: Space Telescope Science Institute
Pierre-Olivier Lagage: Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM
Jérémy Leconte: Université de Bordeaux
Monika Lendl: Université de Genève
Joshua D. Lothringer: Utah Valley University
Luigi Mancini: Max Planck Institute for Astronomy
Thomas Mikal-Evans: Max Planck Institute for Astronomy
Karan Molaverdikhani: Max Planck Institute for Astronomy
Nikolay K. Nikolov: Space Telescope Science Institute
Kazumasa Ohno: University of California, Santa Cruz
Enric Palle: Instituto de Astrofísica de Canarias (IAC)
Caroline Piaulet: Université de Montréal
Seth Redfield: Wesleyan University
Pierre-Alexis Roy: Université de Montréal
Shang-Min Tsai: University of California, Riverside
Olivia Venot: Université Paris Cité and Université Paris-Est Creteil, CNRS, LISA
Peter J. Wheatley: University of Warwick

Nature, 2023, vol. 620, issue 7973, 292-298

Abstract: 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 Telescope1–3. 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 analysis3–12. 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’, $${\rm{M/H}}=1.0{3}_{-0.51}^{+1.11}$$ M/H = 1.0 3 − 0.51 + 1.11 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.

Date: 2023
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DOI: 10.1038/s41586-023-06230-1

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