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| Titel |
How Enceladus Powers the Saturnian Magnetosphere |
| VerfasserIn |
C. T. Russell, J. S. Leisner, Y. D. Jia, K. K. Khurana, M. K. Dougherty |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250021689
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| Zusammenfassung |
| The Enceladus plume is pumping about 1028 water group molecules into the saturnian
magnetosphere per second, or about one-quarter of the rate of atmospheric loss of Io in the
much larger jovian magnetosphere. In turn, about one-quarter of that material appears to be
ionized in the inner magnetosphere. The seven Enceladus encounters to date (E0 - E6) show
that the outgassing rate has been steady within a factor of two over the last three years. While
it is clear that the addition of Enceladus-derived plasma to the magnetosphere must be the
ultimate source of energy to drive magnetospheric processes, it is not clear how the
magnetospheric phenomena are driven. A key concept that is not included in current
numerical and phenomenological models is the balance between centripetal and
centrifugal forces during the interaction of the plume with the corotating plasma.
When the magnetospheric plasma approaches Enceladus, centrifugal force stretches
the magnetic field line outward. This force is balanced by the inward centripetal
force of the curvature in the stretched field. When the plasma reaches the plume, it
exchanges charge with the plume and a stream of fast neutrals sprays the region
around Enceladus with a disk of neutral atoms and molecules. The magnetic field
line, released of its centrifugal force (but not its mass), is pulled inward and then
slowly accelerated again. When it is accelerated to corotational speed, the flux
tube returns to near its original location. This circulation pattern is powered by the
rotation of the planet but is in quasi-harmonic resonance with the 1.37 day period of
Enceladus. Thus, the wave so forced can build up to a significant amplitude and
this may explain the circulation pattern proposed by Gurnett et al. to explain the
observed density modulation. We note that the region of exact resonance with the
SKR period lies just inside the orbit of Enceladus in the region expected to be the
post-Enceladus-interaction reacceleration region. We note that the same process occurs at Io
in the jovian magnetosphere possibly accounting for the Io ribbon and the system IV rotation
period. |
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