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


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.


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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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Correspondence to J. T. Clarke.

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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).

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