Skip to main content

Thank you for visiting 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:

No sodium in the vapour plumes of Enceladus


The discovery of water vapour and ice particles erupting from Saturn’s moon Enceladus fuelled speculation that an internal ocean was the source1,2,3. Alternatively, the source might be ice warmed, melted or crushed by tectonic motions4. Sodium chloride (that is, salt) is expected to be present in a long-lived ocean in contact with a rocky core. Here we report a ground-based spectroscopic search for atomic sodium near Enceladus that places an upper limit on the mixing ratio in the vapour plumes orders of magnitude below the expected ocean salinity5. The low sodium content of escaping vapour, together with the small fraction of salt-bearing particles6, argues against a situation in which a near-surface geyser is fuelled by a salty ocean through cracks in the crust1. The lack of observable sodium in the vapour is consistent with a wide variety of alternative eruption sources, including a deep ocean6, a freshwater reservoir, or ice. The existing data may be insufficient to distinguish between these hypotheses.

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

Access options

Buy this article

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

Figure 1: Observing geometry and corresponding sodium D-line spectrum of Enceladus and nearby E ring.
Figure 2: Determining the 4 × 10 -7 upper limit for direct sodium ejection into a south-directed plume.
Figure 3: Determining the 7 × 10-6 upper limit for a molecular source, with panels displaying the same information as in Fig. 2 .

Similar content being viewed by others


  1. Porco, C. C. et al. Cassini observes the active south pole of Enceladus. Science 311, 1393–1401 (2006)

    Article  ADS  CAS  Google Scholar 

  2. Spencer, J. R. et al. Cassini encounters Enceladus: background and the discovery of a south polar hot spot. Science 311, 1401–1405 (2006)

    Article  ADS  CAS  Google Scholar 

  3. McKay, C. P., Porco, C. C., Altheide, T., Davis, W. L. & Kral, T. A. The possible origin and persistence of life on Enceladus and detection of biomarkers in the plume. Astrobiology 8, 909–919 (2008)

    Article  ADS  CAS  Google Scholar 

  4. Nimmo, F., Spencer, J. R., Pappalardo, R. T. & Mullen, M. E. Shear heating as the origin of the plumes and heat flux on Enceladus. Nature 447, 289–291 (2007)

    Article  ADS  CAS  Google Scholar 

  5. Zolotov, M. Y. An oceanic composition on early and today's Enceladus. Geophys. Res. Lett. 34 L23203 10.1029/2007GL031234 (2007)

    Article  ADS  Google Scholar 

  6. Postberg, F. et al. Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus. Nature 10.1038/nature08046 (this issue)

  7. Brown, R. A. in Exploration of the Planetary System (eds Woszczyk, A. & Iwaniszewska, C.) 527–531 (Proc. IAU Symp. No. 65, Reidel, 1974)

    Book  Google Scholar 

  8. Brown, M. E. & Hill, R. E. Discovery of an extended sodium atmosphere around Europa. Nature 380, 229–231 (1996)

    Article  ADS  CAS  Google Scholar 

  9. Potter, A. E. & Morgan, T. H. Discovery of sodium in the atmosphere of Mercury. Science 229, 651–653 (1985)

    Article  ADS  CAS  Google Scholar 

  10. Potter, A. E. & Morgan, T. H. Discovery of sodium and potassium vapor in the atmosphere of the Moon. Science 241, 675–680 (1988)

    Article  ADS  CAS  Google Scholar 

  11. Levin, B. J. On the reported Na tails of comets. Icarus 4, 497–499 (1964)

    Article  ADS  Google Scholar 

  12. Lellouch, E., Paubert, G., Moses, J. I., Schneider, N. M. & Strobel, D. F. Volcanically emitted sodium chloride as a source for Io's neutral clouds and plasma torus. Nature 421, 45–47 (2003)

    Article  ADS  CAS  Google Scholar 

  13. Vogt, S. S. et al. HIRES: the high resolution echelle spectrometer on the Keck 10-m telescope. Proc. SPIE 2198, 362–375 (1994)

    Article  ADS  CAS  Google Scholar 

  14. Diego, F., Charalambous, A., Fish, A. C. & Walker, D. D. Final tests and commissioning of the UCL echelle spectrograph. Proc. SPIE 1235, 562–576 (1990)

    Article  ADS  CAS  Google Scholar 

  15. Osterbrock, D. E. et al. Night-sky high-resolution spectral atlas of OH and O2 emission lines for echelle spectrograph wavelength calibration. Publ. Astron. Soc. Pacif. 108, 277–308 (1996)

    Article  ADS  Google Scholar 

  16. Hansen, C. J. et al. Enceladus' water vapor plume. Science 311, 1422–1425 (2006)

    Article  ADS  CAS  Google Scholar 

  17. Tian, F. et al. Monte Carlo simulations of the water vapor plumes on Enceladus. Icarus 188, 154–161 (2007)

    Article  ADS  CAS  Google Scholar 

  18. Jurac, S. et al. Saturn: search for a missing water source. Geophys. Res. Lett. 29 2172 10.1029/2002GL015855 (2002)

    Article  ADS  CAS  Google Scholar 

  19. Burger, M. H. Io's Neutral Clouds: From the Atmosphere to the Plasma Torus. Ph.D. thesis, Univ. Colorado (2003)

    Google Scholar 

  20. Burger, M. H. & Johnson, R. E. Europa’s neutral cloud: morphology and comparisons to Io. Icarus 171, 557–560 (2004)

    Article  ADS  CAS  Google Scholar 

  21. Burger, M. H. et al. Understanding the escape of water from Enceladus. J. Geophys. Res. 112 A06219 10.1029/2002GL015855 (2007)

    Article  ADS  CAS  Google Scholar 

  22. Kieffer, S. W. et al. A clathrate reservoir hypothesis for Enceladus' south polar plume. Science 314, 1764–1766 (2006)

    Article  ADS  CAS  Google Scholar 

  23. Schmidt, J., Brillantov, N., Spahn, F. & Kempf, S. Slow dust in Enceladus' plume from condensation and wall collisions in tiger stripe fractures. Nature 451, 685–688 (2008)

    Article  ADS  CAS  Google Scholar 

  24. Hunter Waite, J. et al. Cassini ion and neutral mass spectrometer: Enceladus plume composition and structure. Science 311, 1419–1422 (2006)

    Article  ADS  Google Scholar 

Download references


Some of the data presented here were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the financial support of the W.M. Keck Foundation. We also acknowledge the Anglo-Australian Telescope and its staff. This work was supported by the National Science Foundation’s Planetary Astronomy Program and the NASA Postdoctoral Program. This paper has benefited from discussions with M. Zolotov, J. Spencer, C. Porco, T. Johnson, A. Ingersoll, W. McKinnon, C. Mackay, F. Postberg, J. Schmidt, S. Kempf and R. Pappalardo.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Nicholas M. Schneider.

Supplementary information

Supplementary Information

This file contains Supplementary Data and Notes and Supplementary References. (PDF 156 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Cite this article

Schneider, N., Burger, M., Schaller, E. et al. No sodium in the vapour plumes of Enceladus. Nature 459, 1102–1104 (2009).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


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.


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