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| Titel |
Seven Years (2004-2011) of Cassini Measurements Reveal Strong Local Time Asymmetry of the Saturnian Ring Current |
| VerfasserIn |
N. Sergis, S. Krimigis, M. Thomsen, E. Roelof, D. Mitchell, D. Hamilton, N. Krupp, M. Dougherty, F. Crary |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250061720
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| Zusammenfassung |
| The Saturnian ring current, initially inferred from magnetic field and particle measurements
after the Voyager 1 and 2 flybys, has been studied in substantial detail via in-situ and remote
measurements since the July 2004 Cassini orbit insertion. The ring current of Saturn, located
between 7 and 15 RS and primarily composed of O+ ions, is characterized by increased
suprathermal (> 3 keV) particle pressure with high (> 1) plasma β values and
intense dynamic behavior, as revealed by the analysis of combined particle data from
the Cassini Magnetospheric Imaging Instrument (MIMI) and the Cassini Plasma
Spectrometer instrument (CAPS), and magnetic field measurements from the Cassini
magnetometer (MAG). Among the most important findings so far is that the azimuthal ring
current flows primarily to balance inertial centrifugal forces inside ~8 RS, but
increasingly it is driven by the non-thermal pressure gradient beyond its maximum region
(8-12 RS, 100–150 pA/m2) and certainly it dominates farther out. Beyond ~ 10RS,
the non-thermal pressure decreases with radial distance faster than the previously
assumed 1/r rate and results in a magnetic perturbation of 10-15 nT. In this work we
present the most complete (2004-2011) and up-to-date results, focusing on the
local time asymmetry of the ring current properties (e.g. particle pressure, current
density), and the relative contribution of different components to the radial force
balance. The comprehensive spatial and local time coverage provided by the Cassini
orbits has revealed that the suprathermal pressure and its corresponding pressure
gradient is higher by a factor of 3 to 8 on the night side, in agreement with the
observed distribution of energetic particle injections and energetic neutral atom
(ENA) emissions. In addition to in-situ measurements, ENA images from the Ion and
Neutral Camera (INCA) of Cassini, offer a unique overview of large parts of the
Saturnian magnetosphere, depicting the rotation and dynamics of the ring current. |
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