Dynamics of energetic particles and neutrals in Saturn's variable magnetosphere: results from the MIMI investigation
Abstract
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.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #37
- Pub Date:
- August 2005
- Bibcode:
- 2005DPS....37.0604K