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Complex structure within Saturn’s infrared aurora

Nature volume 456, pages 214–217 (2008)Cite this article

Abstract

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.

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

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Acknowledgements

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

  1. Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK

    Tom Stallard, Emma J. Bunce, Stan W. H. Cowley, Sarah V. Badman & Dean L. Talboys

  2. Department of Physics and Astronomy, Atmospheric Physics Laboratory, University College London, Gower Street, London WC1E 6BT, UK,

    Steve Miller, Makenzie Lystrup & Nicholas Achilleos

  3. Department of Space and Climate Physics, Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK,

    Christopher S. Arridge

  4. Department of Physics, Space and Atmospheric Physics Group, Imperial College of Science, Technology and Medicine, South Kensington Campus, London SW7 2AZ, UK

    Michele K. Dougherty

  5. Lunar and Planetary Laboratory and Steward Observatory, University of Arizona, Tucson, Arizona 85721-0092, USA ,

    Robert H. Brown

  6. Jet Propulsion Laboratory, California Institute of Technology, M/S 183-601, 4800 Oak Grove Drive, Pasadena, California 91109-8099, USA ,

    Kevin H. Baines, Bonnie J. Buratti & Christophe Sotin

  7. US Geological Survey, Denver, Colorado 80225, USA ,

    Roger N. Clark

  8. Astronomy Department, Cornell University, Ithaca, New York 14853, USA,

    Phil D. Nicholson

  9. Observatoire de Paris, Meudon 92195, France

    Pierre Drossart

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Correspondence to Tom Stallard.

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Stallard, T., Miller, S., Lystrup, M. et al. Complex structure within Saturn’s infrared aurora. Nature 456, 214–217 (2008). https://doi.org/10.1038/nature07440

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