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Jovian-like aurorae on Saturn


Planetary aurorae are formed by energetic charged particles streaming along the planet’s magnetic field lines into the upper atmosphere from the surrounding space environment. Earth’s main auroral oval is formed through interactions with the solar wind1, whereas that at Jupiter is formed through interactions with plasma from the moon Io inside its magnetic field (although other processes form aurorae at both planets2,3). At Saturn, only the main auroral oval has previously been observed and there remains much debate over its origin. Here we report the discovery of a secondary oval at Saturn that is 25 per cent as bright as the main oval, and we show this to be caused by interaction with the middle magnetosphere around the planet. This is a weak equivalent of Jupiter’s main oval, its relative dimness being due to the lack of as large a source of ions as Jupiter’s volcanic moon Io. This result suggests that differences seen in the auroral emissions from Saturn and Jupiter are due to scaling differences in the conditions at each of these two planets, whereas the underlying formation processes are the same.

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Figure 1: H 3 + aurora emission and the associated line-of-sight velocity.
Figure 2: The location of the spectrometer slit on Saturn’s southern aurora.
Figure 3: ‘Jovian-like’ aurorae on Saturn.


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We thank the NASA Infrared Telescope Facility (IRTF) telescope operators for their continued support and expert advice in making these observations possible. The authors are part of the Europlanet European planetary science network, supported by the European Union’s Framework 6 programme. This work was supported by the UK Science and Technology Facilities Council, with postdoctoral fellowships for T.S., N.A. and E.J.B., and a senior fellowship for M.D. T.S. is now funded by an RCUK Fellowship. H.M. was supported by a postgraduate studentship from the UK Engineering and Physical Sciences Research Council. S.W.H.C. was supported by a Royal Society Leverhulme Trust Senior Research Fellowship. T.S., H.M. and M.L. are visiting astronomers at the IRTF, which is operated by the University of Hawaii under Cooperative Agreement no. NCC 5-538 with the NASA Science Mission Directorate, Planetary Astronomy Program.

Author Contributions T.S. designed the study, collected and analysed data and wrote the paper. S.M. collected and aided data analysis. H.M. and M.L. aided data analysis. S.W.H.C., E.J.B, N.A. and M.D. provided the magnetospheric context. All authors discussed the results and commented on the manuscript.

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Correspondence to Tom Stallard.

Supplementary information

Supplementary information

The file contains Supplementary Figure 1 with Legend and Supplementary Discussion. This discussion shows the effect of changing the location of the modelled oval away from the statistically averaged UV oval used in the paper. Moving the oval towards the planetary limb weakens the secondary auroral oval, but does not change its location with respect to the break down in corotation. (PDF 91 kb)

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

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