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.

Complex structure within Saturn’s infrared aurora


The majority of planetary aurorae are produced by electrical currents flowing between the ionosphere and the magnetosphere which accelerate energetic charged particles that hit the upper atmosphere. At Saturn, these processes collisionally excite hydrogen, causing ultraviolet emission1,2,3,4,5,6,7,8, and ionize the hydrogen, leading to H3+ infrared emission9,10,11,12,13,14,15. Although the morphology of these aurorae is affected by changes in the solar wind6,11, the source of the currents which produce them is a matter of debate16,17. Recent models predict only weak emission away from the main auroral oval18. Here we report images that show emission both poleward and equatorward of the main oval (separated by a region of low emission). The extensive polar emission is highly variable with time, and disappears when the main oval has a spiral morphology; this suggests that although the polar emission may be associated with minor increases in the dynamic pressure from the solar wind, it is not directly linked to strong magnetospheric compressions. This aurora appears to be unique to Saturn and cannot be explained using our current understanding of Saturn’s magnetosphere. The equatorward arc of emission exists only on the nightside of the planet, and arises from internal magnetospheric processes that are currently unknown.

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

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Quiescent auroral conditions.
Figure 2: Spiral auroral morphology.
Figure 3: Bright polar auroral emission.


  1. Sandel, B. R. et al. Extreme ultraviolet observations from the Voyager 2 encounter with Saturn. Science 215, 548–553 (2005)

    Article  ADS  Google Scholar 

  2. Trauger, J. T. et al. Saturn’s hydrogen aurora: Wide field and planetary camera 2 imaging from the Hubble Space Telescope. J. Geophys. Res. 103, 20237–20244 (1998)

    Article  ADS  Google Scholar 

  3. Gérard, J.-C. et al. Characteristics of Saturn’s FUV aurora observed with the Space Telescope Imaging Spectrograph. J. Geophys. Res. 109, A09207 (2004)

    ADS  Google Scholar 

  4. Clarke, J. T. et al. Morphological differences between Saturn’s ultraviolet aurorae and those of Earth and Jupiter. Nature 433, 717–719 (2005)

    Article  ADS  CAS  Google Scholar 

  5. Grodent, D., Gérard, J.-C., Cowley, S. W. H., Bunce, E. J. & Clarke, J. T. Variable morphology of Saturn’s southern ultraviolet aurora. J. Geophys. Res. 110, A07215 (2005)

    Article  ADS  Google Scholar 

  6. Bunce, E. J. et al. Cassini observations of the interplanetary medium upstream of Saturn and their relation to Hubble Space Telescope auroral data. Adv. Space Res. 38, 806–814 (2006)

    Article  ADS  Google Scholar 

  7. Badman, S. V., Cowley, S. W. H., Gérard, J.-C. & Grodent, D. A statistical analysis of the location and width of Saturn’s southern auroras. Ann. Geophys. 24, 3533–3545 (2006)

    Article  ADS  Google Scholar 

  8. Bunce, E. J. et al. Origins of Saturn’s aurora: Simultaneous observations by Cassini and the Hubble Space Telescope. J. Geophys. Res. 113, A09209 (2008)

    ADS  Google Scholar 

  9. Stallard, T. et al. The H3 + latitudinal profile of Saturn. Astrophys. J. 521, L149–L152 (1999)

    Article  ADS  CAS  Google Scholar 

  10. Stallard, T., Miller, S., Trafton, L. M., Geballe, T. R. & Joseph, R. D. Ion winds in Saturn’s southern auroral/polar region. Icarus 167, 204–211 (2004)

    Article  ADS  CAS  Google Scholar 

  11. Stallard, T. et al. Saturn’s auroral/polar H3 + infrared emission I: General morphology and ion velocity structure. Icarus 189, 1–13 (2007)

    Article  ADS  CAS  Google Scholar 

  12. Stallard, T. et al. Saturn’s auroral/polar H3 + infrared emission II: A comparison with plasma flow models. Icarus 191, 678–690 (2007)

    Article  ADS  Google Scholar 

  13. Melin, H., Miller, S., Stallard, T., Trafton, L. M. & Geballe, T. R. Variability in the H3 + emission of Saturn: Consequences for ionisation rates and temperature. Icarus 186, 234–241 (2007)

    Article  ADS  CAS  Google Scholar 

  14. Stallard, T. et al. Jovian-like aurorae on Saturn. Nature 453, 1083–1085 (2008)

    Article  ADS  CAS  Google Scholar 

  15. Stallard, T., Lystrup, M. & Miller, S. Emission-line imaging of Saturn’s H3 + aurora. Astrophys. J. 675, L117–L120 (2008)

    Article  ADS  CAS  Google Scholar 

  16. Cowley, S. W. H., Bunce, E. J. & O’Rourke, J. M. A simple quantitative model of plasma flows and currents in Saturn’s polar ionosphere. J. Geophys. Res. 109, A05212 (2004)

    Article  ADS  Google Scholar 

  17. Sittler, E. C., Blanc, M. F. & Richardson, J. D. Proposed model for Saturn’s auroral response to the solar wind: Centrifugal instability model. J. Geophys. Res. 111, A06208 (2006)

    ADS  Google Scholar 

  18. Cowley, S. W. H. & Bunce, E. J. Corotation-driven magnetosphere-ionosphere coupling currents in Saturn’s magnetosphere and their relation to the auroras. Ann. Geophys. 21, 1691–1707 (2003)

    Article  ADS  Google Scholar 

  19. Pryor, W. R. et al. Auroral movies and spectroscopy from Cassini UVIS. Abstract no. P31A–0187 (Fall Meeting, American Geophysical Union, 2007)

    Google Scholar 

  20. Drossart, P. et al. Mapping the H3 + aurora on Saturn from Cassini/VIMS observations. Bull. Am. Astron. Soc. 37, 657 (2005)

    ADS  Google Scholar 

  21. Cowley, S. W. H. et al. Reconnection in a rotation-dominated magnetosphere and its relation to Saturn’s auroral dynamics. J. Geophys. Res. 110, A02201 (2005)

    ADS  Google Scholar 

  22. Grodent, D. et al. Jupiter’s polar auroral emissions. J. Geophys. Res. 108, 1366–1374 (2003)

    Article  Google Scholar 

  23. Stallard, T., Miller, S., Millward, G. & Joseph, R. D. On the dynamics of the Jovian ionosphere and thermosphere II: The measurement of H3 + vibrational temperature, column density, and total emission. Icarus 156, 498–514 (2002)

    Article  ADS  CAS  Google Scholar 

  24. Millward, G., Miller, S., Stallard, T., Aylward, A. & Achilleos, N. On the dynamics of the Jovian ionosphere and thermosphere III: The modelling of auroral conductivity. Icarus 160, 95–104 (2002)

    Article  ADS  Google Scholar 

  25. Baker, D. N., Higbie, P. R., Hones, E. W. & Belian, R. D. High resolution energetic particle measurements at 6.6RE 3. Low energy electron anisotropies and short-term substorm predictions. J. Geophys. Res. 83, 4863–4868 (1978)

    Article  ADS  CAS  Google Scholar 

  26. Hill, T. W. The Jovian auroral oval. J. Geophys. Res. 106, 8101–8108 (2001)

    Article  ADS  Google Scholar 

Download references


This work was supported by a Research Councils UK Fellowship (T.S.) and by the UK Science and Technology Facilities Council (N.A., S.V.B., D.L.T., C.S.A., E.J.B., M.K.D.). The European authors are part of the Europlanet European Planetology Network, supported by the European Union’s Sixth Framework Programme.

Author Contributions T.S. analysed the data and wrote the paper; S.M., M.L. and N.A. aided data analysis; E.J.B., C.S.A., M.K.D., S.W.H.C., S.V.B. and D.L.T. provided discussion as members of the UK MAG-VIMS collaboration team; and R.H.B., K.H.B., B.J.B., R.N.C., C.S., P.D.N. and P.D. provided the reduced data and discussion as members of the Cassini VIMS team. All authors commented on the manuscript.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Tom Stallard.

Supplementary information

Supplementary Information

This file contains a Supplementary Discussion, Supplementary Data and Supplementary References. (PDF 68 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Stallard, T., Miller, S., Lystrup, M. et al. Complex structure within Saturn’s infrared aurora. Nature 456, 214–217 (2008).

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