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Published Online March 22, 2007
Science DOI: 10.1126/science.1138562

Reports

Submitted on December 7, 2006
Accepted on March 7, 2007

The Variable Rotation Period of the Inner Region of Saturn's Plasma Disk

D. A. Gurnett 1, A. M. Persoon 1, W. S. Kurth 1, J. B. Groene 1, T. F. Averkamp 1, M. K. Dougherty 2, D. J. Southwood 3

1 Department of Physics and Astronomy, University of Iowa, IA 52242, USA.
2 Blackett Laboratory, Imperial College, London SW72AZ, UK.
3 Blackett Laboratory, Imperial College, London SW72AZ, UK; European Space Agency, 75738 Paris, France.

We show that the plasma and magnetic fields in the inner region of Saturn's plasma disk rotate in synchronism with the time-variable modulation period of Saturn's kilometric radio emission. This relationship suggests that the radio modulation has its origins in the inner region of the plasma disk, most likely from a centrifugally driven convective instability and an associated plasma outflow that slowly slips in phase relative to Saturn's internal rotation. The slippage rate is determined by the electrodynamic coupling of the plasma disk to Saturn and by the drag force exerted by its interaction with the Enceladus neutral gas torus.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)