HR: 16:00h
AN: P54A-01 INVITED     [Abstracts]
TI: Implications of Cassini UVIS Observations of Neutral Gas in the Saturn Magnetosphere
AU: * Shemansky, D E
EM: dons@hippolyta.usc.edu
AF: D. Shemansky, University of Southern California, Los Angeles, CA 90089 United States
AU: Esposito, L
EM: larry.esposito@lasp.colorado.edu
AF: L. Esposito, University of Colorado, Boulder, CO 80303 United States
AU: Team, C U
EM: candics.j.hansen@jpl.nasa.gov
AF: Cassini UVIS team, JPL, Pasadena, CA 91109 United States
AB: \noindent Images of emission from atomic oxygen and hydrogen in the Saturn magnetosphere have been obtained in the Cassini pre orbit insertion period using the Cassini UVIS imaging spectrometers. Over the period December 25, 2003 - May 12, 2004, the atomic oxygen shows temporal variability in total abundance as well as spatial distribution on a $\sim$2 month time scale. The atomic oxygen is measurable to at least $\pm$ 10 R$_{S}$ in the orbital plane and $\pm$ 4 R$_{S}$ in the polar dimension. The atomic hydrogen is detectable to $\pm$ 45 R$_{S}$ in the orbital plane and projected to be measurable to $\pm$ 20 R$_{S}$ polar. The oxygen emission peaks in the 2 R$_{S}$ - 4 R$_{S}$ region in the orbital plane in a generally asymmetric distribution in local time, with greater abundance on the dark side of the planet. The hydrogen distribution is also asymmetric, showing an extensive anti-sunward component. The magnitude of the variation in oxygen abundance as well as the rate estimated from charge capture in the plasma sheet indicates $\sim$ 500 Mkg loss over a 2 month period. The generation of water product gas from the local solids at this rate implies that mass the equivalent of the E-ring micron sized population is removed on this time scale. A projection to the total mass of the E-ring indicates a characteristic time of $\sim$ 100 My. The erosion of available solids requires a large surface area, and rapid surface reaction rates. A proposed mechanism involves the formation of solid state cluster ions produced in the reaction of low energy plasma sheet ions with micron sized grains, followed by rapid dissociative recombination into the vacuum.
UR: http://lasp.colorado.edu/cassini
DE: 2700 MAGNETOSPHERIC PHYSICS
DE: 2730 Magnetosphere--inner
DE: 2732 Magnetosphere interactions with satellites and rings
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting