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An ultrahot gas-giant exoplanet with a stratosphere

Evans, Thomas M. and Knutson, Heather (2017) An ultrahot gas-giant exoplanet with a stratosphere. Nature, 548 (7665). pp. 58-61. ISSN 0028-0836.

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[img] Image (JPEG) (Extended Data Figure 1: Spectroscopic light curves for WASP-121b) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 2: Model thermal spectrum for WASP-121b broken down by emission source and absorption cross-sections of important molecules) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 3: A comparison of models with and without stratospheres) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 4: Self-consistent models in radiative-convective equilibrium) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 5: Posterior distributions from MCMC retrieval analysis for WASP-121b) - Supplemental Material
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[img] Image (JPEG) (Extended Data Figure 6: ATMO retrieval code applied to WASP-43b thermal emission data) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 1: Parameter values for the WASP-121b white light curve fit) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 2: WFC3 spectroscopic eclipse depths for WASP-121b) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 3: Comparison of different retrieval analyses for WASP-121b) - Supplemental Material
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[img] Image (JPEG) (Extended Data Table 4: MCMC retrieval analysis results for WASP-121b) - Supplemental Material
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[img] Archive (ZIP) (This file contains an archive of ASCII files containing reduced HST data products and models used in the paper) - Supplemental Material
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Infrared radiation emitted from a planet contains information about the chemical composition and vertical temperature profile of its atmosphere. If upper layers are cooler than lower layers, molecular gases will produce absorption features in the planetary thermal spectrum. Conversely, if there is a stratosphere—where temperature increases with altitude—these molecular features will be observed in emission. It has been suggested that stratospheres could form in highly irradiated exoplanets, but the extent to which this occurs is unresolved both theoretically and observationally. A previous claim for the presence of a stratosphereremains open to question, owing to the challenges posed by the highly variable host star and the low spectral resolution of the measurements. Here we report a near-infrared thermal spectrum for the ultrahot gas giant WASP-121b, which has an equilibrium temperature of approximately 2,500 kelvin. Water is resolved in emission, providing a detection of an exoplanet stratosphere at 5σ confidence. These observations imply that a substantial fraction of incident stellar radiation is retained at high altitudes in the atmosphere, possibly by absorbing chemical species such as gaseous vanadium oxide and titanium oxide.

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Evans, Thomas M.0000-0001-5442-1300
Knutson, Heather0000-0002-0822-3095
Alternate Title:A stratosphere in an ultra-hot gas giant exoplanet
Additional Information:© 2017 Macmillan Publishers Limited, part of Springer Nature. Received 08 February 2017; Accepted 07 June 2017; Published online 02 August 2017. This work is based on observations with the NASA/ESA HST, obtained at the Space Telescope Science Institute (STScI) operated by AURA, Inc. This work is also based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 336792 and is supported by the ERC Horizon 2020 research and innovation programme (grant agreement no. 724427). Support for this work was provided by NASA through grants under the HST-GO-14767 “Panchromatic Comparative Exoplanetary Treasury (PanCET)” programme from the STScI. J.G. acknowledges support from a Leverhulme Trust Research Project Grant. H.R.W acknowledges support from the NASA Postdoctoral Program, administered by Universities Space Research Association through a contract with NASA. M.S.M. acknowledges support from the NASA Exoplanets Research Program. J.K.B. acknowledges support from a Royal Astronomical Society Fellowship. D.E. and V.B. acknowledge the financial support of the National Centre for Competence in Research “PlanetS” supported by the Swiss National Science Foundation (SNSF). A.L.E. acknowledges support from CNES and the French Agence Nationale de la Recherche (ANR), under programme ANR-12-BS05-0012 “Exo-Atmos”. J.S.-F. acknowledges support from the Spanish MINECO through grant AYA2014-54348-C3-2-R. G.W.H. acknowledges support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence programme. L.B.-J. and P.L. acknowledge support from CNES (France) under project PACES. P.T. and D.S.A. acknowledge funding from the European Research Council under the European Union Seventh Framework Program: grant 247060-PEPS. Contributions: T.M.E. and D.K.S. designed the HST observations of WASP-121. D.K.S. and M.L.-M. led the HST Treasury programme, with support provided by all authors. T.M.E. led the HST data analysis with contributions from N.N., H.R.W. and D.D. D.D. proposed and designed the Spitzer observations and analysed the data. D.K.S. led the retrieval analysis. T.K., J.G., M.S.M., A.L.E. and P.T. provided additional theoretical interpretation of the data. R.L. provided molecular absorption cross-sections for the theoretical interpretation. T.M.E. wrote the manuscript along with D.K.S., T.K., M.S.M. and A.L.E. All authors discussed the results and commented on the paper. The author list ordering is alphabetical after M.S.M. The authors declare no competing financial interests.
Group:Astronomy Department
Funding AgencyGrant Number
European Research Council (ERC)336792
European Research Council (ERC)724427
Leverhulme TrustUNSPECIFIED
NASA Postdoctoral ProgramUNSPECIFIED
Royal Astronomical SocietyUNSPECIFIED
Swiss National Science Foundation (SNSF)UNSPECIFIED
Centre National d'Études Spatiales (CNES)UNSPECIFIED
Agence Nationale de la Recherche (ANR)ANR-12-BS05-0012
Ministerio de Economía y Competitividad (MINECO)AYA2014-54348-C3-2-R
Tennessee State UniversityUNSPECIFIED
State of TennesseeUNSPECIFIED
European Research Council (ERC)247060-PEPS
Issue or Number:7665
Record Number:CaltechAUTHORS:20170602-143102428
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77925
Deposited By: George Porter
Deposited On:04 Aug 2017 23:03
Last Modified:20 Apr 2020 08:47

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