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Morphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter

Abstract

It has often been stated that Saturn's magnetosphere and aurorae are intermediate between those of Earth, where the dominant processes are solar wind driven1, and those of Jupiter, where processes are driven by a large source of internal plasma2,3,4. But this view is based on information about Saturn that is far inferior to what is now available. Here we report ultraviolet images of Saturn, which, when combined with simultaneous Cassini measurements of the solar wind5 and Saturn kilometric radio emission6, demonstrate that its aurorae differ morphologically from those of both Earth and Jupiter. Saturn's auroral emissions vary slowly; some features appear in partial corotation whereas others are fixed to the solar wind direction; the auroral oval shifts quickly in latitude; and the aurora is often not centred on the magnetic pole nor closed on itself. In response to a large increase in solar wind dynamic pressure5 Saturn's aurora brightened dramatically, the brightest auroral emissions moved to higher latitudes, and the dawn side polar regions were filled with intense emissions. The brightening is reminiscent of terrestrial aurorae, but the other two variations are not. Rather than being intermediate between the Earth and Jupiter, Saturn's auroral emissions behave fundamentally differently from those at the other planets.

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Figure 1: Ultraviolet images of Saturn's southern aurora from HST STIS.
Figure 2: Variations in Saturn's auroral power and radius of the oval.

References

  1. Milan, S. E. et al. Variations in polar cap area during two substorm cycles. Ann. Geophys. 21, 1121–1140 (2003)

    Article  ADS  Google Scholar 

  2. Hill, T. W. Auroral structures at Jupiter and Earth. Adv. Space Res. 33, 2021–2031 (2004)

    Article  ADS  Google Scholar 

  3. Hill, T. W. The Jovian auroral oval. J. Geophys. Res. 106, 8101–8107 (2001)

    Article  ADS  Google Scholar 

  4. Cowley, S. W. H. & Bunce, E. J. Origin of the main auroral oval in Jupiter's coupled magnetosphere-ionosphere system. Planet. Space Sci. 49, 1067–1088 (2001)

    Article  ADS  Google Scholar 

  5. Crary, F. et al. Solar wind dynamic pressure and electric field as the main factors controlling Saturn's aurorae. Nature doi:10.1038/nature03333 (this issue)

  6. Kurth, W. et al. An Earth-like correspondence between Saturn's auroral features and radio emission. Nature doi:10.1038/nature03334 (this issue)

  7. Sandel, B. R. & Broadfoot, A. L. Morphology of Saturn's aurora. Nature 292, 679–682 (1981)

    Article  ADS  CAS  Google Scholar 

  8. 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 

  9. Richardson, J. D. Thermal ions at Saturn: Plasma parameters and implications. J. Geophys. Res. 91, 1381–1389 (1986)

    Article  ADS  CAS  Google Scholar 

  10. Trauger, J. T. et al. Saturn's hydrogen aurora: WFPC 2 imaging from the Hubble Space Telescope. J. Geophys. Res. E 103, 20237–20244 (1998)

    Article  ADS  Google Scholar 

  11. Cowley, S. W. H., Bunce, E. J. & Prangé, R. Saturn's polar ionospheric flows and their relation to the main auroral oval. Ann. Geophys. 21, 1–16 (2003)

    Article  Google Scholar 

  12. Gérard, J.-C. et al. Characteristics of Saturn's FUV aurora observed with the Space Telescope Imaging Spectrograph. J. Geophys. Res. 109, A09207, doi:10.1029/2004JA010513 (2004)

    ADS  Google Scholar 

  13. Judge, D. L., Wu, F. & Carlson, R. Ultraviolet observations of the saturnian system. Science 207, 431–434 (1980)

    Article  ADS  CAS  Google Scholar 

  14. Broadfoot, A. L. et al. Extreme ultraviolet observations from Voyager 1 encounter with Saturn. Science 212, 206–211 (1981)

    Article  ADS  CAS  Google Scholar 

  15. Clarke, J. T. et al. IUE detection of bursts of H Ly-alpha from Saturn. Nature 290, 226–227 (1981)

    Article  ADS  CAS  Google Scholar 

  16. McGrath, M. & Clarke, J. T. HI Lyman alpha emission from Saturn (1980-1990). J. Geophys. Res. A 97, 13691–13703 (1992)

    Article  ADS  Google Scholar 

  17. Prangé, R. et al. A CME-driven interplanetary shock traced from the Sun to Saturn by planetary auroral emissions. Nature (in the press)

Download references

Acknowledgements

This work is based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by AURA, Inc., for NASA. The research was supported by grants from STScI and NASA to Boston University. J.C.G. and D.G. acknowledge support from the Belgian Fund for Scientific Research and the PRODEX programme of ESA. S.W.H.C. was supported by a PPARC senior fellowship, and E.J.B. by a PPARC post-doctoral fellowship. F.C., W.K. and T.H. acknowledge support from the NASA/JPL Cassini project.

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Clarke, J., Gérard, JC., Grodent, D. et al. Morphological differences between Saturn's ultraviolet aurorae and those of Earth and Jupiter. Nature 433, 717–719 (2005). https://doi.org/10.1038/nature03331

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