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Formation of Saturn's ring spokes by lightning‐induced electron beams
Author(s) -
Jones G. H.,
Krupp N.,
Krüger H.,
Roussos E.,
Ip W.H.,
Mitchell D. G.,
Krimigis S. M.,
Woch J.,
Lagg A.,
Fränz M.,
Dougherty M. K.,
Arridge C. S.,
McAndrews H. J.
Publication year - 2006
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl028146
Subject(s) - saturn , radius , thunderstorm , lightning (connector) , electron precipitation , rings of saturn , physics , electron , magnetosphere of saturn , van allen radiation belt , midnight , astronomy , meteorology , magnetosphere , magnetic field , planet , magnetopause , power (physics) , computer security , quantum mechanics , computer science
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.