Jones, GH; Krupp, N; Kruger, H; Roussos, E; Ip, WH; Mitchell, DG; Krimigis, SM; ... McAndrews, HJ; + view all Jones, GH; Krupp, N; Kruger, H; Roussos, E; Ip, WH; Mitchell, DG; Krimigis, SM; Woch, J; Lagg, A; Franz, M; Dougherty, MK; Arridge, CS; McAndrews, HJ; - view fewer (2006) Formation of Saturn's ring spokes by lightning-induced electron beams. Geophysical Research Letters , 33 (21) , Article L21202. 10.1029/2006GL028146.

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Abstract

Spokes are near-linear markings sometimes visible on Saturn's rings. They are widely accepted as being electrostatically-levitated sheets of similar to 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.

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