Visible-to-near-infrared observations indicate that the cloud top of the main cloud deck on Uranus lies at a pressure level of between 1.2 bar and 3 bar. However, its composition has never been unambiguously identified, although it is widely assumed to be composed primarily of either ammonia or hydrogen sulfide (H2S) ice. Here, we present evidence of a clear detection of gaseous H2S above this cloud deck in the wavelength region 1.57–1.59 μm with a mole fraction of 0.4–0.8 ppm at the cloud top. Its detection constrains the deep bulk sulfur/nitrogen abundance to exceed unity (>4.4–5.0 times the solar value) in Uranus’s bulk atmosphere, and places a lower limit on the mole fraction of H2S below the observed cloud of \((1.0-2.5)\times 1{0}^{-5}\). The detection of gaseous H2S at these pressure levels adds to the weight of evidence that the principal constituent of 1.2–3-bar cloud is likely to be H2S ice.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Additional information

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


  1. 1.

    de Kleer, K., Luszcz-Cook, S., de Pater, I., Ádámkovics, M. & Hammel, H. B. Clouds and aerosols on Uranus: radiative transfer modeling of spatially-resolved near-infrared Keck spectra. Icarus 256, 120–137 (2015).

  2. 2.

    Irwin, P. G. J. et al. The application of new methane line absorption data to Gemini-N/NIFS and KPNO/FTS observations of Uranus’ near-infrared spectrum. Icarus 220, 369–382 (2012).

  3. 3.

    Sromovsky, L. A., Fry, P. M. & Kim, J. H. Methane on Uranus: the case for a compact CH4 cloud layer at low latitudes and a severe CH4 depletion at high latitudes based on a re-analysis of Voyager occultation measurements and STIS spectroscopy. Icarus 215, 292–312 (2011).

  4. 4.

    Weidenschilling, S. J. & Lewis, J. S. Atmospheric and cloud structures of the Jovian planets. Icarus 20, 465–476 (1973).

  5. 5.

    de Pater, I., Romani, P. N. & Atreya, S. K. Possible microwave absorption by H2S gas in Uranus’ and Neptune’s atmospheres. Icarus 91, 220–233 (1991).

  6. 6.

    de Pater, I., Romani, P. N. & Atreya, S. K. Uranus’ deep atmosphere revealed. Icarus 82, 288–313 (1989).

  7. 7.

    de Pater, I. & Massie, S. Models of the millimeter-centimeter spectra of the giant planets. Icarus 62, 143–171 (1985).

  8. 8.

    Cameron, A. G. W. in Essays in Nuclear Astrophysics (eds C. A. Barnes et al.) 23–43 (Cambridge Univ. Press, London, 1982).

  9. 9.

    Niemann, H. B. et al. The composition of the Jovian atmosphere as determined by the Galileo probe mass spectrometer. J. Geophys. Res. 103, 22831–22845 (1998).

  10. 10.

    Boissier, J. et al. Interferometric imaging of the sulfur-bearing molecules H2S, SO and CS in comet C/1995 O1 (Hale-Bopp). Astron. Astrophys. 475, 1131–1144 (2007).

  11. 11.

    Eberhardt, P., Meier, R., Krankowsky, D. & Hodges, P. R. Methanol and hydrogen sulfide in comet P/Halley. Astron. Astrophys. 288, 315–329 (1994).

  12. 12.

    Noll, K. S. et al. HST spectroscopic observations of Jupiter after the collision of comet Shoemaker-Levy 9. Science 267, 1307–1313 (1995).

  13. 13.

    Lellouch, E. Chemistry induced by the impacts: observations. In Proc. Space Telescope Science Institute Workshop (eds Noll, K. S. et al.) 213–242 (Vol. 156, IAU Colloquium, Cambridge Univ. Press, Cambridge, 1996).

  14. 14.

    Campargue, A., Leshchishina, O., Wang, L., Mondelain, D. & Kassi, S. The WKLMC empirical line lists (5852–7919 cm−1) for methane between 80 K and 296 K: ‘final’ lists for atmospheric and planetary applications. J. Molec. Spectrosc. 291, 16–22 (2013).

  15. 15.

    Rothman, L. S. et al. The HITRAN2012 molecular spectroscopic database. J. Quant. Spectrosc. Ra. 130, 4–50 (2013).

  16. 16.

    Irwin, P. G. J. et al. Uranus’ cloud structure and seasonal variability from Gemini-North and UKIRT observations. Icarus 212, 339–350 (2011).

  17. 17.

    Irwin, P. G. J. et al. Further seasonal changes in Uranus’ cloud structure observed by Gemini-North and UKIRT. Icarus 218, 47–55 (2012).

  18. 18.

    Irwin, P. G. J. et al. The NEMESIS planetary atmosphere radiative transfer and retrieval tool. J. Quant. Spectrosc. Ra . 109, 1136–1150 (2008).

  19. 19.

    Karkoschka, E. & Tomasko, M. The haze and methane distributions on Uranus from HST-STIS spectroscopy. Icarus 202, 287–309 (2009).

  20. 20.

    Fray, N. & Schmitt, B. Sublimation of ices of astrophysical interest: a bibliographic review. Plan. Space Sci. 57, 2053–2080 (2009).

  21. 21.

    Irwin, P. G. J. et al. Reanalysis of Uranus’ cloud scattering properties from IRTF/SpeX observations using a self-consistent scattering cloud retrieval scheme. Icarus 250, 462–476 (2015).

  22. 22.

    Karkoschka, E. & Tomasko, M. Methane absorption coefficients for the jovian planets from laboratory, Huygens, and HST data. Icarus 205, 674–694 (2010).

  23. 23.

    Sromovsky, L. A. & Fry, P. M. Spatially resolved cloud structure on Uranus: implications of near-IR adaptive optics imaging. Icarus 192, 527–557 (2007).

  24. 24.

    Orton, G. S. et al. Mid-infrared spectroscopy of Uranus from the Spitzer Infrared Spectrometer: 1. determination of the mean temperature of the upper troposphere and stratosphere. Icarus 243, 494–513 (2014).

  25. 25.

    Grevesse, N., Asplund, M. & Sauval, A. D. The solar chemical composition. Space Sci. Rev. 130, 105–114 (2007).

  26. 26.

    Lodders. K. in Principles and Perspectives in Cosmochemistry (eds Goswami, A. & Reddy, B. E.) 379–417 (Astrophysics and Space Science Proc., Springer-Verlag Berlin Heidelberg, Berlin, 2010).

  27. 27.

    Campargue, A. et al. An empirical line list for methane in the 1.26–1.71 μm region for planetary investigations (T = 80–300 K). Application to Titan. Icarus 219, 110–128 (2012).

  28. 28.

    Feuchtgruber, H. et al. The D/H ratio in the atmospheres of Uranus and Neptune from Herschel-PACS observations. Astron. Astrophys. 551, A126 (2013).

  29. 29.

    Lécluse, C., Robert, F., Gautier, D. & Guiraud, M. Deuterium enrichment in giant planets. Planet. Space Sci. 44, 1579–1592 (1996).

  30. 30.

    Pine, A. S. Self-, N2-, O2-, H2-, Ar-, and He- broadening in the v 3 band Q branch of CH4. J. Chem. Phys. 97, 773–785 (1992).

  31. 31.

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

  32. 32.

    Margolis, J. S. Hydrogen broadening and collision-induced line shifts of methane at 4200 cm−1. J. Quant. Spectrosc. Ra. 49, 71–79 (1993).

  33. 33.

    Varanasi, P. & Chudamani, S. The temperature dependence of lineshifts, linewidths and line intensities of methane at low temperatures. J. Quant. Spectrosc. Ra. 43, 1–11 (1990).

  34. 34.

    Hartmann, J.-M. et al. A far wing lineshape for H2-broadened CH4 infrared transitions. J. Quant. Spectrosc. Ra. 72, 117–122 (2002).

  35. 35.

    de Bergh, C. et al. Applications of a new set of methane line parameters to the modeling of Titan’s spectrum in the 1.58 μm window. Planet. Space Sci. 61, 85–98 (2012).

  36. 36.

    Sromovsky, L. A., Fry, P. M., Boudon, V., Campargue, A. & Nikitin, A. Comparison of line-by-line and band models of near-IR methane absorption applied to outer planet atmospheres. Icarus 218, 1–23 (2012).

  37. 37.

    Azzam, A. A. A., Tennyson, J., Yurchenko, S. N. & Naumenko, O. V. ExoMol molecular line lists—XVI: the rotation-vibration spectrum of hot H2S. Mon. Not. Roy. Ast. Soc. 460, 4063–4074 (2016).

  38. 38.

    Lacis, A. A. & Oinas, V. A description of the correlated-k distribution method for modelling nongray gaseous absorption, thermal emission, and multiple scattering in vertically inhomogeneous atmospheres. J. Geophys. Res. 96, 9027–9063 (1991).

  39. 39.

    Plass, G. N., Kattawar, G. W. & Catchings, F. E. Matrix operator method of radiative transfer. 1: Rayleigh scattering. Appl. Opt. 12, 314–329 (1973).

  40. 40.

    Borysow, A. Modeling of collision-induced infrared absorption spectra of H2–H2 pairs in the fundamental band at temperatures from 20 to 300 K. Icarus 92, 273–279 (1991).

  41. 41.

    Borysow, A. New model of collision-induced infrared absorption spectra of H2–He pairs in the 2–2.5 μm range at temperatures from 20 to 300 K—an update. Icarus 96, 169–175 (1992).

  42. 42.

    Zheng, C. & Borysow, A. Modeling of collision-induced infrared absorption spectra of H2 pairs in the first overtone band at temperatures from 20 to 500 K. Icarus 113, 84–90 (1995).

  43. 43.

    Menang, K. P., Coleman, M. D., Gardiner, T. D., Ptashnik, I. V. & Shine, K. P. A high-resolution near-infrared extraterrestrial solar spectrum derived from ground-based Fourier transform spectrometer measurements. J. Geophys. Res. 118, 5319–5331 (2013).

  44. 44.

    Fiorenza, C. & Formisano, V. A solar spectrum for PFS data analysis. Planet. Space Sci. 53, 1009–1016 (2005).

  45. 45.

    Thuillier, G. et al. The solar spectral irradiance from 200 to 2400 nm as measured by the SOLSPEC spectrometer from the ATLAS and EURECA missions. Sol. Phys. 214, 1–22 (2003).

  46. 46.

    Sheik-Bahae, M. in Encyclopedia of Modern Optics (eds Guenther, R. D. et al.) 234–239 (Academic Press, Amsterdam, 2005).

  47. 47.

    Mishchenko, M. I., Travis, L. D., Khan, R. A. & West, R. A. Modeling phase functions for dustlike tropospheric aerosols using a shape mixture of randomly oriented polydisperse spheroids. J. Geophys. Res. 102, 16831–16847 (1997).

Download references


We are grateful to the United Kingdom Science and Technology Facilities Council for funding this research and to our support astronomers: R. McDermid and C. Trujillo. The Gemini Observatory is operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Science and Technology Facilities Council (United Kingdom), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). We thank L. Sromovsky for providing the code used to generate our Rayleigh-scattering opacities. G.A.O. was supported by NASA funding to the Jet Propulsion Laboratory, California Institute of Technology. L.N.F. was supported by a Royal Society Research Fellowship at the University of Leicester.

Author information


  1. Department of Physics (Atmospheric, Oceanic and Planetary Physics), University of Oxford, Oxford, UK

    • Patrick G. J. Irwin
    • , Daniel Toledo
    •  & Ryan Garland
  2. School of Earth Sciences, University of Bristol, Bristol, UK

    • Nicholas A. Teanby
  3. Department of Physics & Astronomy, University of Leicester, Leicester, UK

    • Leigh N. Fletcher
  4. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

    • Glenn A. Orton
  5. LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 6, Université Paris-Diderot, Sorbonne Paris Cité, Meudon, France

    • Bruno Bézard


  1. Search for Patrick G. J. Irwin in:

  2. Search for Daniel Toledo in:

  3. Search for Ryan Garland in:

  4. Search for Nicholas A. Teanby in:

  5. Search for Leigh N. Fletcher in:

  6. Search for Glenn A. Orton in:

  7. Search for Bruno Bézard in:


P.G.J.I. wrote the proposal to make the original observations, and reduced and reanalysed the data using the NEMESIS code; B.B. and R.G. assisted in identifying and validating the line data used. G.A.O. provided the Spitzer temperature–pressure profile used. All authors contributed to the analysis and interpretation of the results, and all authors wrote the final paper.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Patrick G. J. Irwin.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–12.

About this article

Publication history






Further reading