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A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b
Coulombe, Louis-Philippe ; Benneke, Björn ; Challener, Ryan ; Piette, Anjali A. A. ; Wiser, Lindsey S. ; Mansfield, Megan ; MacDonald, Ryan J. ; Beltz, Hayley ; Feinstein, Adina D. ; Radica, Michael ... show 10 more
Coulombe, Louis-Philippe
Benneke, Björn
Challener, Ryan
Piette, Anjali A. A.
Wiser, Lindsey S.
Mansfield, Megan
MacDonald, Ryan J.
Beltz, Hayley
Feinstein, Adina D.
Radica, Michael
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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’, 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.
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Date
2023-05-31
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Nature Research
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Keywords
Exoplanets, Atmospheric chemistry, Atmospheric dynamics
Citation
Coulombe LP, Benneke B, Challener R, Piette AAA, Wiser LS, Mansfield M, MacDonald RJ, Beltz H, Feinstein AD, Radica M, Savel AB, Dos Santos LA, Bean JL, Parmentier V, Wong I, Rauscher E, Komacek TD, Kempton EM, Tan X, Hammond M, Lewis NT, Line MR, Lee EKH, Shivkumar H, Crossfield IJM, Nixon MC, Rackham BV, Wakeford HR, Welbanks L, Zhang X, Batalha NM, Berta-Thompson ZK, Changeat Q, Désert JM, Espinoza N, Goyal JM, Harrington J, Knutson HA, Kreidberg L, López-Morales M, Shporer A, Sing DK, Stevenson KB, Aggarwal K, Ahrer EM, Alam MK, Bell TJ, Blecic J, Caceres C, Carter AL, Casewell SL, Crouzet N, Cubillos PE, Decin L, Fortney JJ, Gibson NP, Heng K, Henning T, Iro N, Kendrew S, Lagage PO, Leconte J, Lendl M, Lothringer JD, Mancini L, Mikal-Evans T, Molaverdikhani K, Nikolov NK, Ohno K, Palle E, Piaulet C, Redfield S, Roy PA, Tsai SM, Venot O, Wheatley PJ. A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b. Nature. 2023 Aug;620(7973):292-298. doi: 10.1038/s41586-023-06230-1. Epub 2023 May 31. PMID: 37257843; PMCID: PMC10412449