Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

An ultrahot gas-giant exoplanet with a stratosphere

Nature volume 548, pages 58–61 (2017)Cite this article

Subjects

Abstract

Infrared radiation emitted from a planet contains information about the chemical composition and vertical temperature profile of its atmosphere1,2,3. If upper layers are cooler than lower layers, molecular gases will produce absorption features in the planetary thermal spectrum4,5. Conversely, if there is a stratosphere—where temperature increases with altitude—these molecular features will be observed in emission6,7,8. It has been suggested that stratospheres could form in highly irradiated exoplanets9,10, but the extent to which this occurs is unresolved both theoretically11,12 and observationally3,13,14,15. A previous claim for the presence of a stratosphere14 remains open to question, owing to the challenges posed by the highly variable host star and the low spectral resolution of the measurements3. 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.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Wavelength-integrated white light curve for WASP-121b.
Figure 2: Emission spectrum for WASP-121b.
Figure 3: Temperature–pressure profiles for WASP-121b.

Similar content being viewed by others

References

  1. Madhusudhan, N. & Seager, S. A temperature and abundance retrieval method for exoplanet atmospheres. Astrophys. J. 707, 24–39 (2009)

    Article  ADS  CAS  Google Scholar 

  2. Line, M. R. et al. A systematic retrieval analysis of secondary eclipse spectra. I. A comparison of atmospheric retrieval techniques. Astrophys. J. 775, 137 (2013)

    Article  ADS  CAS  Google Scholar 

  3. Line, M. R. et al. No thermal inversion and a solar water abundance for the hot Jupiter HD 209458b from HST/WFC3 spectroscopy. Astrophys. J. 152, 203 (2016)

    Google Scholar 

  4. Stevenson, K. B. et al. Thermal structure of an exoplanet atmosphere from phase-resolved emission spectroscopy. Science 346, 838–841 (2014)

    Article  ADS  CAS  PubMed  Google Scholar 

  5. Beatty, T. G. et al. Evidence for atmospheric cold-trap process in the non-inverted emission spectrum of Kepler-13Ab using HST/WFC3. Preprint at https://arxiv.org/abs/1612.06409 (2016)

  6. Gillett, F. C., Low, F. J. & Stein, W. A. The 2.8–14-micron spectrum of Jupiter. Astrophys. J. 157, 925–934 (1969)

    Article  ADS  CAS  Google Scholar 

  7. Ridgway, S. T. Jupiter: identification of ethane and acetylene. Astrophys. J. 187, L41–L43 (1974)

    Article  ADS  CAS  Google Scholar 

  8. Wallace, L., Prather, M. & Belton, M. J. S. The thermal structure of the atmosphere of Jupiter. Astrophys. J. 193, 481–493 (1974)

    Article  ADS  CAS  Google Scholar 

  9. Fortney, J. J., Lodders, K., Marley, M. S. & Freedman, R. S. A unified theory for the atmospheres of the hot and very hot Jupiters: two classes of irradiated atmospheres. Astrophys. J. 678, 1419–1435 (2008)

    Article  ADS  CAS  Google Scholar 

  10. Hubeny, I., Burrows, A. & Sudarsky, D. A possible bifurcation in atmospheres of strongly irradiated stars and planets. Astrophys. J. 594, 1011–1018 (2003)

    Article  ADS  CAS  Google Scholar 

  11. Burrows, A., Budaj, J. & Hubeny, I. Theoretical spectra and light curves of close-in extrasolar giant planets and comparison with data. Astrophys. J. 678, 1436–1457 (2008)

    Article  ADS  CAS  Google Scholar 

  12. Spiegel, D. S., Silverio, K. & Burrows, A. Can TiO explain thermal inversions in the upper atmospheres of irradiated giant planets? Astrophys. J. 699, 1487–1500 (2009)

    Article  ADS  CAS  Google Scholar 

  13. Knutson, H. A., Charbonneau, D., Allen, L. A., Burrows, A. & Megeath, S. T. The 3.6–8.0μm broadband emission spectrum of HD209458b: evidence for an atmospheric temperature inversion. Astrophys. J. 673, 526–531 (2008)

    Article  ADS  CAS  Google Scholar 

  14. Haynes, K., Mandell, A. M., Madhusudhan, N., Deming, D. & Knutson, H. Spectroscopic evidence for a temperature inversion in the dayside atmosphere of hot Jupiter WASP-33b. Astrophys. J. 806, 146 (2015)

    Article  ADS  Google Scholar 

  15. Wong, I. et al. 3.6 and 4.5 μm Spitzer phase curves of the highly irradiated hot Jupiters WASP-19b and HAT-P-7b. Astrophys. J. 823, 122 (2016)

    Article  ADS  Google Scholar 

  16. Cartier, K. M. S. et al. Near-infrared emission spectrum of WASP-103b using Hubble Space Telescope/Wide Field Camera 3. Astron. J. 153, 34 (2017)

    Article  ADS  CAS  Google Scholar 

  17. Crouzet, N., McCullough, P. R., Deming, D. & Madhusudhan, N. Water vapor in the spectrum of the extrasolar planet HD 189733b. II. The eclipse. Astrophys. J. 795, 166 (2014)

    Article  ADS  CAS  Google Scholar 

  18. Wilkins, A. N. et al. The emergent 1.1–1.7 μm spectrum of the exoplanet COROT-2b as measured using the Hubble Space Telescope. Astrophys. J. 783, 113 (2014)

    Article  ADS  CAS  Google Scholar 

  19. Evans, T. M. et al. Detection of H2O and evidence for TiO/VO in an ultra-hot exoplanet atmosphere. Astrophys. J. 822, L4 (2016)

    Article  ADS  CAS  Google Scholar 

  20. Delrez, L. et al. WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star. Mon. Not. R. Astron. Soc. 458, 4025–4043 (2016)

    Article  ADS  CAS  Google Scholar 

  21. Sharp, C. M. & Burrows, A. Atomic and molecular opacities for brown dwarf and giant planet atmospheres. Astrophys. J. Suppl. Ser. 168, 140–166 (2007)

    Article  ADS  CAS  Google Scholar 

  22. Wakeford, H. R. & Sing, D. K. Transmission spectral properties of clouds for hot Jupiter exoplanets. Astron. Astrophys. 573, A122 (2015)

    Article  ADS  CAS  Google Scholar 

  23. Guillot, T. On the radiative equilibrium of irradiated planetary atmospheres. Astron. Astrophys. 520, A27 (2010)

    Article  ADS  MATH  Google Scholar 

  24. Marley, M. S. & McKay, C. P. Thermal structure of Uranus’ atmosphere. Icarus 138, 268–286 (1999)

    Article  ADS  CAS  PubMed  Google Scholar 

  25. Hickey, M. P., Walterscheid, R. L. & Schubert, G. Gravity wave heating and cooling in Jupiter’s thermosphere. Icarus 148, 266–281 (2000)

    Article  ADS  Google Scholar 

  26. Matcheva, K. I. & Strobel, D. F. Heating of Jupiter’s thermosphere by dissipation of gravity waves due to molecular viscosity and heat conduction. Icarus 140, 328–340 (1999)

    Article  ADS  Google Scholar 

  27. Heng, K., Hayek, W., Pont, F. & Sing, D. K. On the effects of clouds and hazes in the atmospheres of hot Jupiters: semi-analytical temperature-pressure profiles. Mon. Not. R. Astron. Soc. 420, 20–36 (2012)

    Article  ADS  Google Scholar 

  28. Lodders, K. Titanium and vanadium chemistry in low-mass dwarf stars. Astrophys. J. 577, 974–985 (2002)

    Article  ADS  CAS  Google Scholar 

  29. Sing, D. K. et al. A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion. Nature 529, 59–62 (2016)

    Article  ADS  CAS  PubMed  Google Scholar 

  30. Kirkpatrick, J. D. et al. Discoveries from a near-infrared proper motion survey using multi-epoch Two Micron All-Sky Survey data. Astrophys. J. Suppl. Ser. 190, 100–146 (2010)

    Article  ADS  CAS  Google Scholar 

  31. Hauschildt, P. H., Allard, F. & Baron, E. The NextGen model atmosphere grid for 3,000 ≤ Teff ≤ 10,000 K. Astrophys. J. 512, 377–385 (1999)

    Article  ADS  CAS  Google Scholar 

  32. Deming, D. et al. Infrared transmission spectroscopy of the exoplanets HD 209458b and XO-1b using the Wide Field Camera 3 on the Hubble Space Telescope. Astrophys. J. 774, 95 (2013)

    Article  ADS  CAS  Google Scholar 

  33. Wakeford, H. R. et al. HST PanCET program: a cloudy atmosphere for the promising JWST target WASP-101b. Astrophys. J. 835, L12 (2017)

    Article  ADS  Google Scholar 

  34. Mandel, K. & Agol, E. Analytic light curves for planetary transit searches. Astrophys. J. 580, L171–L175 (2002)

    Article  ADS  Google Scholar 

  35. Foreman-Mackey, D., Hogg, D. W., Lang, D. & Goodman, J. emcee: the MCMC hammer. Publ. Astron. Soc. Pacif. 125, 306–312 (2013)

    Article  ADS  Google Scholar 

  36. Jones, E. et al. SciPy: Open source scientific tools for Python. http://www.scipy.org (2001)

  37. Gelman, A. & Rubin, D. B. Inference from iterative simulation using multiple sequences. Stat. Sci. 7, 457–472 (1992)

    Article  MATH  Google Scholar 

  38. Lewis, N. K. et al. Orbital phase variations of the eccentric giant planet HAT-P-2b. Astrophys. J. 766, 95 (2013)

    Article  ADS  Google Scholar 

  39. Deming, D. et al. Spitzer secondary eclipses of the dense, modestly-irradiated, giant exoplanet HAT-P-20b using pixel-level decorrelation. 805, 132 (2015)

  40. Amundsen, D. S. et al. Accuracy tests of radiation schemes used in hot Jupiter global circulation models. Astron. Astrophys. 564, A59 (2014)

    Article  Google Scholar 

  41. Amundsen, D. S., Tremblin, P., Manners, J., Baraffe, I. & Mayne, N. J. Treatment of overlapping gaseous absorption bands with the correlated-k method in hot Jupiter and brown dwarf atmosphere models. Astron. Astrophys. 598, A97 (2017)

    Article  ADS  CAS  Google Scholar 

  42. Drummond, B. et al. The effects of consistent chemical kinetics calculations on the pressure-temperature profiles and emission spectra of hot Jupiters. Astron. Astrophys. 594, A69 (2016)

    Article  CAS  Google Scholar 

  43. Tremblin, P. et al. Fingering convection and cloudless models for cool brown dwarf atmospheres. Astrophys. J. 804, L17 (2015)

    Article  ADS  CAS  Google Scholar 

  44. Tremblin, P. et al. Cloudless atmospheres for L/T dwarfs and extrasolar giant planets. Astrophys. J. 817, L19 (2016)

    Article  ADS  CAS  Google Scholar 

  45. Wakeford, H. R. et al. HAT-P-26b: a Neptune-mass exoplanet with a well-constrained heavy element abundance. Science 356, 628–631 (2017)

    Article  ADS  CAS  PubMed  Google Scholar 

  46. Eastman, J., Gaudi, B. S. & Agol, E. EXOFAST: a fast exoplanetary fitting suite in IDL. Publ. Astron. Soc. Pacif. 125, 83–112 (2013)

    Article  ADS  Google Scholar 

  47. Kreidberg, L. et al. A precise water abundance measurement for the hot Jupiter WASP-43b. Astrophys. J. 793, L27 (2014)

    Article  ADS  CAS  Google Scholar 

  48. Stevenson, K. B. et al. Spitzer phase curve constraints for WASP-43b at 3.6 and 4.5 μm. Astron. J. 153, 68 (2017)

    Article  ADS  CAS  Google Scholar 

  49. Rothman, L. S. et al. The HITRAN 2008 molecular spectroscopic database. J. Quant. Spectrosc. Radiat. Transf. 110, 533–572 (2009)

    Article  ADS  CAS  Google Scholar 

  50. Tennyson, J. et al. The ExoMol database: molecular line lists for exoplanet and other hot atmospheres. J. Mol. Spectrosc. 327, 73–94 (2016)

    Article  ADS  CAS  Google Scholar 

  51. Eastman, J., Siverd, R. & Gaudi, B. Scott Achieving better than 1 minute accuracy in the heliocentric and barycentric Julian Dates. Publ. Astron. Soc. Pacif. 122, 935–946 (2010)

    Article  ADS  Google Scholar 

Download references

Acknowledgements

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.

Author information

Authors and Affiliations

  1. Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, UK

    Thomas M. Evans, David K. Sing, Jayesh Goyal & Nikolay Nikolov

  2. NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, 91109, California, USA

    Tiffany Kataria

  3. NASA Goddard Space Flight Center, Greenbelt, 20771, Maryland, USA

    Hannah R. Wakeford & Avi M. Mandell

  4. Department of Astronomy, University of Maryland, College Park, 20742, Maryland, USA

    Drake Deming

  5. NASA Ames Research Center, MS 245-5, Moffett Field, 94035, California, USA

    Mark S. Marley

  6. Department of Applied Physics and Applied Mathematics, Columbia University, New York, 10025, New York, USA

    David S. Amundsen

  7. NASA Goddard Institute for Space Studies, New York, 10025, New York, USA

    David S. Amundsen

  8. Lunar and Planetary Laboratory, University of Arizona, Tucson, 85721, Arizona, USA

    Gilda E. Ballester

  9. Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK

    Joanna K. Barstow

  10. Sorbonne Universités, UPMC Université Paris 6 and CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis boulevard Arago, Paris, F-75014, France

    Lotfi Ben-Jaffel & Alain Lecavelier des Etangs

  11. Observatoire de l’Université de Genève, 51 chemin des Maillettes, Sauverny, 1290, Switzerland

    Vincent Bourrier & David Ehrenreich

  12. Centre for Star and Planet Formation, Niels Bohr Institute and Natural History Museum, University of Copenhagen, Copenhagen, DK-1350, Denmark

    Lars A. Buchhave

  13. Lowell Center for Space Science and Technology, University of Massachusetts, Lowell, 01854, Massachusetts, USA

    Ofer Cohen

  14. Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Berlin, D-10623, Germany

    Antonio García Muñoz

  15. Center of Excellence in Information Systems, Tennessee State University, Nashville, 37209, Tennessee, USA

    Gregory W. Henry

  16. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, 91125, California, USA

    Heather Knutson

  17. Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR 7331, CNRS, Université de Reims Champagne-Ardenne, Reims, 51687, France

    Panayotis Lavvas

  18. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, 21218, Maryland, USA

    Nikole K. Lewis

  19. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, 02138, Massachusetts, USA

    Mercedes López-Morales

  20. Centro de Astrobiología (CSIC-INTA), ESAC Campus, Camino bajo del Castillo, Villanueva de la Cañada, E-28692, Madrid, Spain

    Jorge Sanz-Forcada

  21. Maison de la Simulation, CEA, CNRS, Université Paris-Sud, UVSQ, Université Paris-Saclay, Gif-sur-Yvette, 91191, France

    Pascal Tremblin

  22. Bay Area Environmental Research Institute, Moffett Field, California, 94035, USA

    Roxana Lupu

Authors
  1. Thomas M. Evans
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. David K. Sing
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Tiffany Kataria
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Jayesh Goyal
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Nikolay Nikolov
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Hannah R. Wakeford
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Drake Deming
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Mark S. Marley
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. David S. Amundsen
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Gilda E. Ballester
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Joanna K. Barstow
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Lotfi Ben-Jaffel
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Vincent Bourrier
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. Lars A. Buchhave
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. Ofer Cohen
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. David Ehrenreich
    View author publications

    You can also search for this author in PubMed Google Scholar

  17. Antonio García Muñoz
    View author publications

    You can also search for this author in PubMed Google Scholar

  18. Gregory W. Henry
    View author publications

    You can also search for this author in PubMed Google Scholar

  19. Heather Knutson
    View author publications

    You can also search for this author in PubMed Google Scholar

  20. Panayotis Lavvas
    View author publications

    You can also search for this author in PubMed Google Scholar

  21. Alain Lecavelier des Etangs
    View author publications

    You can also search for this author in PubMed Google Scholar

  22. Nikole K. Lewis
    View author publications

    You can also search for this author in PubMed Google Scholar

  23. Mercedes López-Morales
    View author publications

    You can also search for this author in PubMed Google Scholar

  24. Avi M. Mandell
    View author publications

    You can also search for this author in PubMed Google Scholar

  25. Jorge Sanz-Forcada
    View author publications

    You can also search for this author in PubMed Google Scholar

  26. Pascal Tremblin
    View author publications

    You can also search for this author in PubMed Google Scholar

  27. Roxana Lupu
    View author publications

    You can also search for this author in PubMed Google Scholar

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.

Corresponding author

Correspondence to Thomas M. Evans.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Reviewer Information Nature thanks K. Heng and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Figure 1 Spectroscopic light curves for WASP-121b.

a–d, Raw normalized light curves for each of the spectroscopic channels with photon-noise 1σ error bars (orange and green circles), and best-fit eclipse signals multiplied by linear time trends (grey lines). Vertical offsets have been applied for visual clarity. Labels indicate central wavelengths for each channel. e–h, Model residuals after removing the best-fit eclipse signal and linear time trend for each of the spectroscopic light curves in a–d, respectively, with photon-noise 1σ error bars (orange and green circles) and stochastic components of the best-fit Gaussian process models (black lines). Note that for most channels, the correlations remaining in the residuals after accounting for a linear time trend are minimal.

Extended Data Figure 2 Model thermal spectrum for WASP-121b broken down by emission source and absorption cross-sections of important molecules.

a, Similar to Fig. 2, showing the HST measurements of the WASP-121b thermal spectrum (brown circles; error bars, 1σ uncertainties). Red line shows the best-fit model (H2O and VO) obtained from the retrieval analysis. Other coloured lines show model thermal spectra generated using the same T–P profile as for the best-fit model but with the opacity due to each molecule turned off one-by-one: VO off (blue line) and H2O off (green line). b, Absorption cross-sections for plausible gas-phase absorbers (colour coded, key at top right) across the WFC3 bandpass. Text labels in the key give the rescaling factors that have been applied to each cross-section to fit them on a single vertical axis, with the exception of the H2O cross-section which has not been rescaled. Note that the VO cross-section has been rescaled by a factor of 0.03, which is consistent with the abundance of VO relative to H2O inferred for the best-fit model (Extended Data Table 4).

Extended Data Figure 3 A comparison of models with and without stratospheres.

a, A sequence of T–P profiles with and without stratospheres computed using the analytic parameterization of ref. 23. The red line corresponds to a model with a strong stratosphere obtained from the MCMC retrieval analysis and the green line shows a model with a weaker stratosphere. The light blue and dark blue lines show, respectively, models with a decreasing temperature profile and a strongly-decreasing temperature profile. The yellow line indicates the best-fit isothermal model with a temperature of 2,700 K. b, Corresponding contribution functions averaged over the WFC3 G141 bandpass, indicating the approximate pressures probed at these wavelengths. c, Corresponding thermal spectra, with H2O and VO bands seen in emission for the models with stratospheres (red and green lines) and in absorption for the models with decreasing temperature profiles (light blue and dark blue lines). The isothermal model has a featureless blackbody spectrum (yellow line).

Extended Data Figure 4 Self-consistent models in radiative-convective equilibrium.

a, Similar to Fig. 2, but showing self-consistent models in radiative equilibrium: median H2O and VO abundances obtained from the retrieval analysis (light blue line); H2O abundance set to median value and VO abundance set to the lower value of the 68% credible range (green line); solar metallicity, but without VO and TiO, and with an arbitrary absorber with absorption cross-section κ = 0.02 cm2 g−1 (pink line); and 15× solar metallicity, but without VO and TiO, and with an arbitrary absorber with κ = 0.06 cm2 g−1 (dark blue line). For the last two models, the arbitrary absorber has grey opacity across the 0.43–1 μm wavelength range and is assumed to be distributed uniformly throughout the atmosphere. The best-fit isothermal model with temperature 2,700 K is also shown (yellow line). Brown circles with error bars, HST data with 1σ uncertainties: inset, HST data on a magnified scale. b, Corresponding T–P profiles, all of which have a stratosphere across the 10−2 bar to 10−5 bar pressure range. Thick lines indicate the main pressure levels probed across the WFC3 G141 bandpass.

Extended Data Figure 5 Posterior distributions from MCMC retrieval analysis for WASP-121b.

Panels along the diagonal show the marginalized posterior distributions for each parameter of the thermal emission model (κIR, γ1, β, H2O abundance, VO abundance), shown left to right in the columns, and top to bottom in the rows. Solid orange lines show the posterior medians and dashed orange lines show the ranges either side encompassing ±34% of the samples. Panels below the diagonal show the posterior distribution as a function of each parameter pair with increasing probability from light to dark shades. As γ1 controls the optical opacity, there is a strong anti-correlation with the radiation efficiency factor β, where lower radiation efficiency values are compensated by higher optical opacities and vice versa. There is also a strong degeneracy between the abundances of each molecule (H2O, VO) and the parameter κIR which controls the overall atmospheric opacity. Higher abundances and higher values of κIR result in stratospheres at lower pressures and vice versa.

Extended Data Figure 6 ATMO retrieval code applied to WASP-43b thermal emission data.

a, Black data points show the measured thermal emission data for WASP-43b taken from ref. 48, composed of HST/WFC3 and Spitzer/IRAC observations. Vertical error bars give 1σ uncertainties and horizontal error bars give photometric bandpasses. The red line shows the best-fit spectrum obtained from an ATMO retrieval analysis, with shading indicating the regions encompassing 68%, 95% and 99.7% of the MCMC samples. The inset shows a magnified view of the HST data. The retrieved volume mixing ratio (VMR) for H2O is in good agreement with the published value obtained using the CHIMERA retrieval code2,3 and the ATMO retrieval achieves a better fit to the data as measured by the minimum χ2. b, Best-fit T–P profiles retrieved with ATMO (solid blue line) and CHIMERA (solid green line). The two analyses agree to within the 68% credible ranges (blue and green dashed lines).

Extended Data Table 1 Parameter values for the WASP-121b white light curve fit
Full size table
Extended Data Table 2 WFC3 spectroscopic eclipse depths for WASP-121b
Full size table
Extended Data Table 3 Comparison of different retrieval analyses for WASP-121b
Full size table
Extended Data Table 4 MCMC retrieval analysis results for WASP-121b
Full size table

Supplementary information

Supplementary Data

This file contains an archive of ASCII files containing reduced HST data products and models used in the paper. (ZIP 329 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Evans, T., Sing, D., Kataria, T. et al. An ultrahot gas-giant exoplanet with a stratosphere. Nature 548, 58–61 (2017). https://doi.org/10.1038/nature23266

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature23266

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing