Plasma density of Saturn's magnetosphere

Details Plasma density of Saturn's magnetosphere Plasma density of Saturn's magnetosphere

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmsm41b..04m&link_type=abstract

American Geophysical Union, Spring Meeting 2008, abstract #SM41B-04

Physics

2731 Magnetosphere: Outer, 6275 Saturn

Scientific paper

We have investigated the electron density below 5 cm-3 in the magnetosphere of Saturn (7-80 RS) statistically using the RPWS Langmuir probe (LP) onboard Cassini. In general, the density distribution showed a clear dependence on the radial distance (L-value) as well as on the distance from equatorial plane (Z), indicates that the plasma is strongly controlled by the centrifugal force. From the characteristics of the density distribution, we have identified the extension of the plasma disc, plasmasheet, lobe, and mantle regions. The electron density of the plasma disc is high (>10-1 cm-3) and it decreases exponentially with increasing the distance from the equatorial plane. This is consistent with the idea that the plasma has originated around the moons in the plasma disc, and is transported outward via the centrifugal force. The plasma disc can extend as far as 15 RS and is confined within |Z|<5 RS. Outside the plasma disc, the density is highly time variable, where the high-density (10-2 - 10-1 cm-3) and low-density (>10-2 cm-3) regions appears quasi- periodic with a periodicity of planet rotation. In this region, the density also decreases exponentially with increasing distance from the equatorial plane, suggesting that the plasma distribution is still largely controlled by the centrifugal force, but the slope is not steep as it is in the plasma disc. The density of the high-density region shows the distribution consistent with the idea that the plasma originating from the plasma disc is transported outward by the centrifugal force. From the density characteristics, we have identified the high-density region as the plasma sheet and the low-density region as the lobe where the plasma escapes from the opened filed line. At high latitudes, the density becomes on average constant, which implies that the centrifugal force control becomes weaker. However, the density variation is still large, and in fact the rotational modulation of the density can be detected everywhere in the dataset. The quasi-periodical high- and low-density region appearance at high latitude can be due to the repetitive entries into the lobe and mantle region of the spacecraft. The density on the dayside had similar characteristics as that on the nightside, but the values were typically about 10 times larger. The density distributions obtained in this study show the strong control of the centrifugal force on the plasma in Saturn's magnetosphere, and will be useful for magnetospheric modelling studies in the future.

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