HR: 1400h
AN: P33A-05    [Abstracts]
TI: Extended Search for Energetic Sodium Ions in Saturn's Magnetosphere
AU: * Christon, S P
EM: spchriston@aol.com
AF: Focused Analysis and Research, Columbia, Columbia, md 21044, United States
AU: Hamilton, D C
EM: dch@umd.edu
AF: University of Maryland, Department of Physics, College Park, College Park, MD 20742, United States
AU: Krimigis, S M
EM: tom.krimigis@jhuapl.edu
AF: Johns Hopkins University, Applied Physics Laboratory, Laurel, Laurel, MD 20723, United States
AU: Mitchell, D G
EM: don.mitchell@jhuapl.edu
AF: Johns Hopkins University, Applied Physics Laboratory, Laurel, Laurel, MD 20723, United States
AB: Instruments on the Cassini spacecraft discovered that Enceladus, an icy satellite of Saturn, ejects plumes of gas, mainly water vapor, and icy grains from so called "tiger stripes" near its South pole. Ice particles emitted from Enceladus form Saturn's large E ring. Both grains and gas can be sources of energetic charged particles through photoionization and/or charged particle impact. Extant sunlight and high-energy charged particle flux allow both processes. Once atoms and molecules are ionized and subsequently accelerated, they can quickly traverse large portions of a planetary magnetosphere before being detected. Sodium (Na) is considered a necessary tracer for a liquid water ocean on Enceladus. Water in contact with Enceladus' rocky interior should become salty. A high-sensitivity telescopic search using ground-based observatories failed to detect sodium emissions near Enceladus [Schneider et al., 2007]. On the other hand, in nearly all in situ measurements of E ring ice particle composition, Cassini's Cosmic Dust Analyzer (CDA) finds sodium in varying concentrations [Postberg et al., 2008]. In this study, we use measurements from MIMI/CHEMS, the Charge-Energy-Mass Spectrometer, to extend our analysis of ion composition in the range >31-220 keV/e taking full note of extant backgrounds in the magnetosphere [Christon et al., 2008]. CHEMS, one of three sensors comprising the MIMI investigation on Cassini, determines the energy, mass, and charge state of ions. In our earlier study, for mid- 2004 through 2006, we found an upper limit for the number ratio of Na⁺¹ ions relative to the more abundant water-group W⁺¹ (O⁺¹, OH⁺¹, and H₂O⁺¹) ions, Na⁺¹/W⁺¹ ∼ 0.0005-0.0010. Our present extended and refined analysis uses data collected for mid-2004 to early- 2009 in the near-equatorial, R < 20 Rs, magnetosphere to better define the in situ measurement of sodium with improved statistics and to examine the relative abundance of other low charge state heavy ion species. References: Christon et al. (2008), Eos Trans. AGU, 89(53), Fall Meet. Suppl., abst. P23B-1383. Postberg et al. (2008), Eos Trans. AGU, 89(53), Fall Meet. Suppl., abst. P14A-03. Schneider et al, (2007), Eos Trans. AGU, 88(52), Fall Meet. Suppl., abst. P11F-08.
DE: 2756 Planetary magnetospheres (5443, 5737, 6033)
DE: 6275 Saturn
DE: 7845 Particle acceleration
DE: 7846 Plasma energization
SC: Planetary Sciences [P]
MN: 2009 Joint Assembly