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GEOPHYSICAL RESEARCH LETTERS,
VOL. 33,
L21202,
6 PP., 2006
doi:10.1029/2006GL028146
Formation of Saturn's ring spokes by lightning-induced electron beams
Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
Institutes of Astronomy and Space Science, National Central University, Chung-li, Taiwan
Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA
Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
The Blackett Laboratory, Imperial College London, London, UK
The Blackett Laboratory, Imperial College London, London, UK
Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Dorking, UK
Spokes are near-linear markings sometimes visible on Saturn's rings. They are widely accepted as being electrostatically-levitated sheets of ∼0.6 micron-radius charged grains. Previously-suggested causes of the grains' charging do not agree with all spoke characteristics, which include their rapid generation, localized formation primarily in Saturn's midnight-dawn sector, the seasonality of their apparitions, and, crucially, their morphologies. We contend that spokes are caused by lightning-induced electron beams striking the rings, at locations magnetically-connected to thunderstorms. This view is supported by a semi-quantitative spoke morphology simulation. Spokes' formation locations are further controlled by Saturn's ionospheric density, which reaches a near-dawn minimum where electron beams can most easily propagate to the rings. The beams may generate observed X-ray emission, supply particles to Saturn's radiation belts, and over time will modify the rings' constituents. Finally, we report Cassini MIMI instrument observations of an electron burst which displays some characteristics expected of a lightning-induced event.
Received 12 September 2006; accepted 10 October 2006; published 9 November 2006.
Citation: (2006), Formation of Saturn's ring spokes by lightning-induced electron beams, Geophys. Res. Lett., 33, L21202, doi:10.1029/2006GL028146.
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