37th DPS Meeting, 4-9 September 2005
Session 6 Cassini I
Invited, Monday, September 5, 2005, 2:00-3:50pm, Music Concert Hall

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[6.04] Dynamics of energetic particles and neutrals in Saturn's variable magnetosphere: results from the MIMI investigation

S.M. Krimigis, D.G. Mitchell (JHUAPL), D.C. Hamilton (UNIV OF MD), N. Krupp (MPI), S. Livi, E.C. Roelof (JHUAPL), J. Dandouras (CESR), B.H. Mauk, P.C. Brandt, C.P. Paranicas, J. Saur (JHUAPL), T.P. Armstrong (FUND TECH), S. Bolton (JPL), A.F. Cheng (JHUAPL), G. Gloeckler (UNIV OF MD), M.E. Hill (JHUAPL), K.C. Hsieh (UNIV OF AZ), W.H. Ip (NATL CENTRAL UNIV), A. Lagg (MPI), L.J. Lanzerotti (BELL LABS), R.W. McEntire, D.J. Williams (JHUAPL)

The Magnetospheric IMaging Instrument (MIMI) comprises three sensors: the Ion and Neutral Camera (INCA) provides images using energetic neutral atoms (ENA) and ions; the Charge-Energy-Mass-Spectrometer (CHEMS) determines the mass and charge state of ions; and the Low Energy Magnetospheric Measurement System (LEMMS) measures ion and electron distributions using a dual field-of-view telescope (Krimigis et al, Space Sci Rev,114, 2333-329, 2004). Measurements by MIMI after Saturn orbit insertion on 1 July 2004 have elucidated several new features of the planet's magnetosphere. These include: (1) A dynamical magnetosphere with an11-hour periodicity. (2) The first remotely-sensed radiation belt inside Saturn's D-ring. (3) Abundant water products in the magnetospheric plasma > or = 10 kev/charge, but little nitrogen (N+/O+<0.05); neutral gas is found to be a major mechanism for particle loss. (4) Injections of plasma in the ~4-11Rs and also >20Rs corotate with the planet and can last for several days. (5) Activity (possibly analogous to Earth's substorms) occurs in Saturn's magnetotail in the 20-40 Rs region during large magnetospheric disturbances; this has not been observed during quiet times. (6) Field-aligned electron beams occur in the dawn to early morning sector as close as ~10 Rs, and map to latitudes of observed Saturn aurora. (7) A gas cloud around Titan with dimensions > 1 Rs, with strong high (~3200 km) altitude ENA emissions forms a continuous, asymmetric ``halo." (8) Titan's emission is centered on moon--hot plasma interaction with the exosphere; changing intensity depends on variable (x10-100) ion population and magnetic field orientation about Titan. (9) Upstream ion events have been measured to large (<50 to > 800 Rs) distances; several are enriched in oxygen ions, suggesting a magnetospheric origin. The observations will be presented and discussed in the context of current models of Saturn's magnetosphere.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.