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| Titel |
The electrons and ion characteristics of Saturn’s plasma disk inside the Enceladus orbit |
| VerfasserIn |
Michiko Morooka, Jan-Erik Wahlund, Sheng-Yi Ye, William Kurth, Ann Persoon, Mika Holmberg |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150182
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| Publikation (Nr.) |
 EGU/EGU2017-14614.pdf |
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| Zusammenfassung |
| Cassini observations revealed that Saturn’s icy moon Enceladus and surrounding E ring are
the significant plasma source of the magnetosphere. However, the observations sometimes
show the electron density enhancement even inside the Enceladus orbiting distance, 4RS.
Further plasma contribution from the inner rings, the G and the F rings and main A
ring are the natural candidate as an additional plasma source. The Cassini/RPWS
Langmuir Probe (LP) measurement provides the characteristics of the electrons and ions
independently in a cold dense plasma. The observations near the center of the E ring
showed that the ion density being larger than the electron density, indicating that
there is additional particle as a negative charge carrier. Those are the small nm and
μm sized dust grains that are negatively charged by the electron attachments. The
faint F and G rings, located at R=2RS and 3RS, consist of small grains and similar
electron/ion density discrepancies can be expected. We will show different types of the LP
observations when Cassini traveled the equator region of the plasma disk down to
3RS. One with the electron density increasing inside 4RS, and another with the
electron density decreasing inside 4RS. During the orbit 016 (2005 doy-284/285),
the electron density continued to increase toward the planet. On the other hand,
the ion currents, the LP measured currents from the negative bias voltage, turn to
decreasing inside 4RS, implying the density decrease of the ions. By comparing the
observed LP ion current characteristics and the modeled values using the obtained
electron density, we found that the characteristic ion mass can be several times
larger than the water ions (AMU=18) that we expected in this region. During the
orbit 015 (2005 doy-266/267), on the other hand, the LP observed sharp electron
density drop near 3RS. The dust signals from the RPWS antenna showed the density
enhancement of the μm sized grains coincide the electron density drop and we have
estimated that the characteristic ion mass can exceed AMU=100. Throughout the whole
Cassini observation near the equator inside 4RS, we didn’t find the case with the
ion densities larger than the electron densities as were found near the E ring and
the Enceladus plume. We suggest that Saturn’s plasmadisk inside the Enceladus
orbit is dynamic in ion characteristics where the water molecules coagulate and
grow into a small icy dust grains. In the presentation we discuss the relationship
between the electron/ion density and the density of the nm and μm sized grains. |
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