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A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations


Ganymede’s atmosphere is produced by charged particle sputtering and sublimation of its icy surface. Previous far-ultraviolet observations of the O i 1,356 Å and O i 1,304 Å oxygen emissions were used to infer sputtered molecular oxygen (O2) as an atmospheric constituent, but an expected sublimated water (H2O) component remained undetected. Here we present an analysis of high-sensitivity spectra and spectral images acquired by the Hubble Space Telescope revealing H2O in Ganymede’s atmosphere. The relative intensity of the oxygen emissions requires contributions from the dissociative excitation of water vapour, indicating that H2O is more abundant than O2 around the subsolar point. Away from the subsolar region, the emissions are consistent with a pure O2 atmosphere. Eclipse observations constrain atomic oxygen to be at least two orders of magnitude less abundant than these other species. The higher H2O/O2 ratio above the warmer trailing hemisphere compared with the colder leading hemisphere, the spatial concentration in the subsolar region and the estimated abundance of ~1015 molecules of H2O per cm2 are consistent with sublimation of the icy surface as source.

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Fig. 1: Ganymede’s orbital longitude during the individual exposures of the three HST visits analysed here.
Fig. 2: COS spectra from exposures 1 and 2.
Fig. 3: Observation of Ganymede’s trailing hemisphere.
Fig. 4: Observation of Ganymede’s leading hemisphere.
Fig. 5: The oxygen emission ratio is diagnostic of the atmospheric composition.

Data availability

All used Hubble Space Telescope data are publicly available at the Mikulski Archive for Space Telescopes ( Source data are provided with this paper.


  1. Johnson, R. E., Lanzerotti, L. J., Brown, W. L. & Armstrong, T. P. Erosion of Galilean satellite surfaces by Jovian magnetosphere particles. Science 212, 1027–1030 (1981).

    Article  ADS  Google Scholar 

  2. Marconi, M. L. A kinetic model of Ganymede’s atmosphere. Icarus 190, 155–174 (2007).

    Article  ADS  Google Scholar 

  3. Orton, G. S., Spencer, J. R., Travis, L. D., Martin, T. Z. & Tamppari, L. K. Galileo photopolarimeter-radiometer observations of Jupiter and the Galilean satellites. Science 274, 389–391 (1996).

    Article  ADS  Google Scholar 

  4. Leblanc, F. et al. On the orbital variability of Ganymede’s atmosphere. Icarus 293, 185–198 (2017).

    Article  ADS  Google Scholar 

  5. Turc, L., Leclercq, L., Leblanc, F., Modolo, R. & Chaufray, J.-Y. Modelling Ganymede’s neutral environment: a 3D test-particle simulation. Icarus 229, 157–169 (2014).

    Article  ADS  Google Scholar 

  6. Plainaki, C. et al. The H2O and O2 exospheres of Ganymede: the result of a complex interaction between the Jovian magnetospheric ions and the icy moon. Icarus 245, 306–319 (2015).

    Article  ADS  Google Scholar 

  7. Shematovich, V. I. Neutral atmosphere near the icy surface of Jupiter’s moon Ganymede. Solar Syst. Res. 50, 262–280 (2016).

    Article  ADS  Google Scholar 

  8. Barth, C. A. et al. Galileo ultraviolet spectrometer observations of atomic hydrogen in the atmosphere at Ganymede. Geophys. Res. Lett. 24, 2147–2150 (1997).

    Article  ADS  Google Scholar 

  9. Feldman, P. D. et al. HST/STIS ultraviolet imaging of polar aurora on Ganymede. Astrophys. J. 535, 1085–1090 (2000).

    Article  ADS  Google Scholar 

  10. Alday, J. et al. New constraints on Ganymede’s hydrogen corona: analysis of Lyman-α emissions observed by HST/STIS between 1998 and 2014. Planet. Space Sci. 148, 35–44 (2017).

    Article  ADS  Google Scholar 

  11. Hall, D. T., Feldman, P. D., McGrath, M. A. & Strobel, D. F. The far-ultraviolet oxygen airglow of Europa and Ganymede. Astrophys. J. 499, 475–481 (1998).

    Article  ADS  Google Scholar 

  12. Doering, J. P. & Gulcicek, E. E. Absolute differential and integral electron excitation cross sections for atomic oxygen. VII—the 3P→1D and 3P→1S transitions from 4.0 to 30 eV. J. Geophys. Res. 94, 1541–1546 (1989).

  13. Johnson, P. V., Kanik, I., Shemansky, D. E. & Liu, X. Electron-impact cross sections of atomic oxygen. J. Phys. B 36, 3203–3218 (2003).

    Article  ADS  Google Scholar 

  14. Makarov, O. P. et al. Kinetic energy distributions and line profile measurements of dissociation products of water upon electron impact. J. Geophys. Res. 109, A09303 (2004).

    ADS  Google Scholar 

  15. Hall, D. T., Strobel, D. F., Feldman, P. D., McGrath, M. A. & Weaver, H. A. Detection of an oxygen atmosphere on Jupiter’s moon Europa. Nature 373, 677–679 (1995).

    Article  ADS  Google Scholar 

  16. Kanik, I. et al. Electron impact dissociative excitation of O2: 2. Absolute emission cross sections of the OI(130.4 nm) and OI(135.6 nm) lines. J. Geophys. Res. 108, 5126 (2003).

    Article  Google Scholar 

  17. Roth, L. et al. Europa’s far ultraviolet oxygen aurora from a comprehensive set of HST observations. J. Geophys. Res. Space Phys. 121, 2143–2170 (2016).

    Article  ADS  Google Scholar 

  18. Cunningham, N. J. et al. Detection of Callisto’s oxygen atmosphere with the Hubble Space Telescope. Icarus 254, 178–189 (2015).

    Article  ADS  Google Scholar 

  19. McGrath, M. A. et al. Aurora on Ganymede. J. Geophys. Res. Space Phys. 118, 2043–2054 (2013).

    Article  ADS  Google Scholar 

  20. Saur, J. et al. The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals. J. Geophys. Res. Space Phys. 120, 1715–1737 (2015).

    Article  ADS  Google Scholar 

  21. Musacchio, F. et al. Morphology of Ganymede’s FUV auroral ovals. J. Geophys. Res. Space Phys. 122, 2855–2876 (2017).

    Article  ADS  Google Scholar 

  22. Molyneux, P. M. et al. Hubble Space Telescope observations of variations in Ganymede’s oxygen atmosphere and aurora. J. Geophys. Res. Space Phys. 123, 3777–3793 (2018).

    Article  ADS  Google Scholar 

  23. Feldman, P. D. et al. Measurements of the near-nucleus coma of comet 67P/Churyumov-Gerasimenko with the Alice far-ultraviolet spectrograph on Rosetta. Astron. Astrophys. 583, A8 (2015).

    Article  Google Scholar 

  24. Paul, D. FUV spectral signatures of molecules and the evolution of the gaseous coma of comet 67P/Churyumov-Gerasimenko. Astron. J. 155, 9 (2018).

    Article  Google Scholar 

  25. Roth, L. et al. Transient water vapor at Europa’s South Pole. Science 343, 171–174 (2014).

    Article  ADS  Google Scholar 

  26. Oza, A. V., Johnson, R. E. & Leblanc, François Dusk/dawn atmospheric asymmetries on tidally-locked satellites: O2 at Europa. Icarus 305, 50–55 (2018).

    Article  ADS  Google Scholar 

  27. Eviatar, A. et al. Excitation of the Ganymede ultraviolet aurora. Astrophys. J. 555, 1013–1019 (2001).

    Article  ADS  Google Scholar 

  28. Carnielli, G. et al. Constraining Ganymede’s neutral and plasma environments through simulations of its ionosphere and Galileo observations. Icarus 343, 113691 (2020).

    Article  Google Scholar 

  29. Eviatar, A., Vasyliūnas, V. M. & Gurnett, D. A. The ionosphere of Ganymede. Planet. Space Sci. 49, 327–336 (2001).

  30. Squyres, S. W. Surface temperatures and retention of H2O frost on Ganymede and Callisto. Icarus 44, 502–510 (1980).

    Article  ADS  Google Scholar 

  31. McGrath, M. A., Lellouch, E., Strobel, D. F., Feldman, P. D. & Johnson, R. E. in Jupiter: The Planet, Satellites and Magnetosphere (eds Bagenal, F. et al.) 457–483 (Cambridge Univ. Press, 2004).

  32. Teolis, B., Tokar, R., Cassidy, T., Khurana, K. & Nordheim, T. in Enceladus and the Icy Moons of Saturn (eds Schenk, P. M. et al.) 361–384 (Univ. Arizona Press, 2018).

  33. Paganini, L. et al. A measurement of water vapour amid a largely quiescent environment on Europa. Nat. Astron. 489, 266–272 (2019).

  34. Weaver, H. A., Feldman, P. D., A’Hearn, M. F. & Arpigny, C. The activity and size of the nucleus of comet Hale-Bopp (C/1995 O1). Science 275, 1900–1904 (1997).

    Article  ADS  Google Scholar 

  35. de Val-Borro, M. et al. Herschel observations of gas and dust in comet C/2006 W3 (Christensen) at 5 AU from the Sun. Astron. Astrophys. 564, A124 (2014).

    Article  Google Scholar 

  36. Spencer, J. R., Lebofsky, L. A. & Sykes, M. V. Systematic biases in radiometric diameter determinations. Icarus 78, 337–354 (1989).

    Article  ADS  Google Scholar 

  37. Feistel, R. & Wagner, W. Sublimation pressure and sublimation enthalpy of H2O ice Ih between 0 and 273.16 K. Geochim. Cosmochim. Acta 71, 36–45 (2007).

    Article  ADS  Google Scholar 

  38. Spencer, J. R. Icy Galilean satellite reflectance spectra: less ice on Ganymede and Callisto? Icarus 70, 99–110 (1987).

    Article  ADS  Google Scholar 

  39. Ligier, N. et al. Surface composition and properties of Ganymede: updates from ground-based observations with the near-infrared imaging spectrometer SINFONI/VLT/ESO. Icarus 333, 496–515 (2019).

    Article  ADS  Google Scholar 

  40. Mura, A. et al. Infrared observations of ganymede from from Juno/Jovian infrared auroral mapper. J. Geophys. Res. Planets 125, e2020JE006508 (2020).

  41. Molyneux, P. M., Nichols, J. D., Becker, T. M., Raut, U. & Retherford, K. D. Ganymede’s far-ultraviolet reflectance: constraining impurities in the surface ice. J. Geophys. Res. Planets 125, e2020JE006476 (2020).

    Article  ADS  Google Scholar 

  42. Prockter, L. M. et al. Dark terrain on Ganymede: geological mapping and interpretation of Galileo Regio at high resolution. Icarus 135, 317–344 (1998).

    Article  ADS  Google Scholar 

  43. Mangold, N. Ice sublimation as a geomorphic process: a planetary perspective. Geomorphology 126, 1–17 (2011).

    Article  ADS  Google Scholar 

  44. de Kleer, K. et al. Ganymede’s surface properties from millimeter and infrared thermal emission. Planet. Sci. J. 2, 5 (2021).

    Article  Google Scholar 

  45. Ingersoll, A. P., Summers, M. E. & Schlipf, S. G. Supersonic meteorology of Io: Sublimation-driven flow of SO 2. Icarus 64, 375–390 (1985).

    Article  ADS  Google Scholar 

  46. Xianzhe, J., Walker, R. J., Kivelson, M. G., Khurana, K. K. & Linker, J. A. Properties of Ganymede’s magnetosphere inferred from improved three-dimensional MHD simulations. J. Geophys. Res. Space Phys. 114, A09209 (2009).

    ADS  Google Scholar 

  47. Duling, S., Saur, J. & Wicht, J. Consistent boundary conditions at nonconducting surfaces of planetary bodies: applications in a new Ganymede MHD model. J. Geophys. Res. Space Phys. 119, 4412–4440 (2014).

    Article  ADS  Google Scholar 

  48. Fatemi, S., Poppe, A. R., Khurana, K. K., Holmström, M. & Delory, G. T. On the formation of Ganymede’s surface brightness asymmetries: kinetic simulations of Ganymede’s magnetosphere. Geophys. Res. Lett. 43, 4745–4754 (2016).

    Article  ADS  Google Scholar 

  49. Plainaki, C. et al. Preliminary estimation of the detection possibilities of Ganymede’s water vapor environment with MAJIS. Planet. Space Sci. 191, 105004 (2020).

    Article  Google Scholar 

  50. Wirström, E. S., Bjerkeli, P., Rezac, L., Brinch, C. & Hartogh, P. Effect of the 3D distribution on water observations made with the SWI. I. Ganymede. Astron. Astrophys. 637, A90 (2020).

    Article  ADS  Google Scholar 

  51. Becker, T. M. et al. The far-UV albedo of Europa from HST observations. J. Geophys. Res. Planets 123, 1327–1342 (2018).

    Article  ADS  Google Scholar 

  52. Roth, L. et al. Constraints on an exosphere at Ceres from Hubble Space Telescope observations. Geophys. Res. Lett. 43, 2465–2472 (2016).

    Article  ADS  Google Scholar 

  53. Morton, D. C. Atomic data for resonance absorption lines. III. Wavelengths longward of the Lyman limit for the elements hydrogen to gallium. Astrophys. J. Suppl. 149, 205–238 (2003).

    Article  ADS  Google Scholar 

  54. Gladstone, G. R. Solar O i 1304-Å triplet line profiles. J. Geophys. Res. 97, 19519–19525 (1992).

    Article  ADS  Google Scholar 

  55. Chandrasekhar, S. Radiative Transfer (Dover, 1960).

    MATH  Google Scholar 

  56. Roth, L., Saur, J., Retherford, K. D., Feldman, P. D. & Strobel, D. F. A phenomenological model of Io’s UV aurora based on HST/STIS observations. Icarus 228, 386–406 (2014).

    Article  ADS  Google Scholar 

  57. McClintock, W. E., Rottman, G. J. & Woods, T. N. Solar-Stellar Irradiance Comparison Experiment II (SOLSTICE II): instrument concept and design. Sol. Phys. 230, 225–258 (2005).

    Article  ADS  Google Scholar 

  58. Kivelson, M. G. et al. in Jupiter: The Planet, Satellites and Magnetosphere (eds Bagenal, F. et al.) 513–536 (Cambridge Univ. Press, 2004).

  59. Roth, L. et al. Constraints on Io’s interior from auroral spot oscillations. J. Geophys. Res. Space Phys. 122, 1903–1927 (2017).

    Article  ADS  Google Scholar 

  60. Ganymede Voyager—Galileo SSI Global Mosaic 1km v1 (United States Geological Survey, 2020);

  61. Kanik, I., Johnson, P. V., Das, M. B., Khakoo, M. A. & Tayal, S. S. Electron-impact studies of atomic oxygen: I. Differential and integral cross sections; experiment and theory. J. Phys. B 34, 2647–2665 (2001).

    Article  ADS  Google Scholar 

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L.R. appreciates the support from the Swedish National Space Agency (SNSA) through grant number 154/17 and the Swedish Research Council (VR) through grant number 2017-04897. J.S. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 884711).

Author information

Authors and Affiliations



L.R. led the study, performed the data analysis and wrote the manuscript. N.I. supported all steps of the data analysis. G.R.G. contributed to the analysis and interpretation of the COS eclipse test. L.R., J.S., D.G. and B.B. planned and performed the 2010 and 2017 HST observations and observing strategy. All authors contributed to the interpretation of results and manuscript writing.

Corresponding author

Correspondence to Lorenz Roth.

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The authors declare no competing interests.

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Peer review informationNature Astronomy thanks Apurva Oza and Audrey Vorburger 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

Extended Data Fig. 1 Count rates at the two oxygen multiplets as a function of time in the COS exposures.

A sharp increase of the OI1304 Å emission (blue) from light scattered in the geocorona can be seen towards the end. No increase due to geocoronal scattered light is present at OI1356 Å (red). For the analysis the last 520 s in each exposure are removed in the processing and only the counts left of the vertical dotted lines are used.

Extended Data Fig. 2 Model atmosphere parameters and results for the corresponding oxygen intensities.

The temperature of the electrons is assumed to be Te = 100 eV. Maps of the model atmospheres are shown in Extended Data Figure 3. Note that the O2 atmosphere produces the vast majority of the OI1356 Å emissions. For the OI1304 Å emissions, in contrast, O2, O and H2O all have relevant contributions to the signal.

Extended Data Fig. 3 Column density maps of the model O2, O and H2O atmospheres.

The H2O atmosphere is scaled for the best-fit on the trailing hemisphere. The O2 and O atmosphere are assumed to be identical on the trailing and leading hemispheres. The derived H2O density for the leading hemisphere is lower by a factor of 6.

Supplementary information

Source Data Fig. 2

Data shown in Fig. 2a,b as plain text.

Source Data Fig. 3

Data shown in Fig. 3d,e as plain text.

Source Data Fig. 4

Data shown in Fig. 4d,e as plain text.

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Roth, L., Ivchenko, N., Gladstone, G.R. et al. A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations. Nat Astron 5, 1043–1051 (2021).

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