The JWST Transiting Exoplanet Community Early Release Science Program
Published May 31, 2023 | Version v1
Dataset Open

Products and Models for "A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b"

Creators

  • 1. Université de Montréal
  • 2. University of Michigan
  • 3. Carnegie Institution for Science
  • 4. Arizona State University
  • 5. University of Arizona
  • 6. Cornell University
  • 7. University of Chicago
  • 8. University of Maryland
  • 9. Space Telescope Science Institute
  • 10. Université Côte d'Azur
  • 11. NASA Goddard Space Flight Center
  • 12. Shanghai Jiao Tong University
  • 13. University of Oxford
  • 14. University of Exeter
  • 15. University of Bern
  • 16. University of Amsterdam

Description

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 and Spitzer Space Telescopes1–3. 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 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 due 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 = 1.03-0.51+1.11 x 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 sub-stellar point that decreases steeply and symmetrically with longitude toward the terminators.

Files

WASP_18b_data_Nature.zip

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Additional details

Related works

Is cited by
Journal article: 10.1038/s41586-023-06230-1 (DOI)