HR: 09:40h
AN: P51D-07 INVITED    [Abstracts]
TI: Rotational Dynamics of Saturn's Magnetosphere
AU: * Mitchell, D G
EM: don.mitchell@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AU: Brandt, P C
EM: pontus.brandt@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AU: Paranicas, C
EM: chris.paranicas@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AU: Carbary, J F
EM: jim.carbary@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AU: Krimigis, S M
EM: tom.krimigis@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AB: Saturn's magnetosphere exhibits periodicities at something close to Saturn's rotation period in many different plasma parameters. Best known is the periodic intensification in the Saturn kilometric radiation (SKR), with observations going back as far as Voyager 25 years ago, and also including Ulysses and Cassini. Although the Voyager SKR results were long assumed to represent Saturn's internal rotation rate, variations in the period of order 0.01 observed first by Ulysses and more recently by Cassini (Kurth et al. 2007) have cast considerable doubt on that scenario. With the reanalysis of the Saturn Pioneer and Voyager magnetometer data by Espinosa et al., 2003, similar periodicities in Saturn's magnetic field were revealed. Cassini measurements have confirmed and refined our characterization of the magnetic rotational signatures, which seem to follow the SKR period quite closely (e.g., Giampieri et al., 2006). Less precisely determined, but with a similar repetition rate, energetic particle periodicities have been identified in the outer magnetosphere (Carbary et al., 2007). Energetic neutral atom emissions also vary nearly sinusoidally at times (Paranicas et al., 2005) at a similar period. Plasma density in the inner magnetosphere also follows the SKR period very closely (Gurnett et al., 2007). At the same time, solar wind effects at Saturn are clearly important, and modify the dynamics of Saturn's&p magnetosphere in very direct ways (Crary et al., 2004; Bunce et al., 2007) as well as more subtly (Cecconi and Zarka 2005). While much of this behavior has been documented, understanding it has been elusive. Models of Saturn, some of which include coupling between the ionosphere and the magnetosphere, have been put forward in the hopes of explaining various features of different data sets. None seem to be sufficient to satisfy all the demands of the data, or at least our understanding of them, at this time. The rotation period exhibited in the data is remarkably stable, yet it varies too much to represent direct driving from the interior. The SKR periodicity is considered to be modulation of a high latitude, field aligned current driven instability. The plasma density at 3 to 5 Rs is clearly on relatively low latitude field lines. The ENA periodicity is on mid-latitude field lines. Coupling between low altitudes and high altitudes should be a strong function of latitude, yet similar periods and stability are observed at both low and high latitudes. The very existence of a rotational periodicity in what appears to be a very symmetric dipole is not explained. What generates the asymmetry? What sustains it over hundreds, perhaps thousands of rotations? How is the period maintained in a system that shows evidence (in both auroral forms [Gerard et al.2006] and in situ plasma [Sittler et al. 2005]) of plasma corotation well below the rate implied by the SKR period? This paper will discuss these mysteries, will try to organize them toward a common explanation, and will concentrate on posing questions that must be answered by any comprehensive model. References not listed, as they exceed the character count.
DE: 2736 Magnetosphere/ionosphere interactions (2431)
DE: 2740 Magnetospheric configuration and dynamics
DE: 5737 Magnetospheres (2756)
DE: 5744 Orbital and rotational dynamics (1221)
DE: 6275 Saturn
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting