HR: 09:35h
AN: P51C-08 INVITED     [Abstracts]
TI: Saturn's A-ring Ionosphere as Observed by the Cassini Ion and Neutral Mass Spectrometer
AU: * Cravens, T E
EM: cravens@ku.edu
AF: Dept. of Physics and Astronomy, University of Kansas , Lawrence, KS 66045 United States
AU: Waite, J H
AF: Dept. of Atmos., Oceanic,and Space Sci., University of Michigan , Ann Arbor, MI 48109 United States
AU: Ip, W T
AF: Institute of Astronomy, National Central University, Chung-Li, 32054 Taiwan
AU: Kazprzak, W T
AF: Code 915, NASA Goddard Spaceflight Center, Greenbelt, MD 20771 United States
AU: Luhmann, J G
AF: Space Science Lab, Univ. of California, Berkeley, CA 94720 United States
AU: McNutt, R L
AF: Applied Physics Lab, John Hopkins Univ., Laurel, MD 20723 United States
AU: Niemann, H B
AF: Code 915, NASA Goddard Spaceflight Center, Greenbelt, MD 20771 United States
AU: Yelle, R V
AF: Lunar and Planetary Lab., University of Arizona, Tucson, AZ 85721 United States
AU: Mueller-Wodarg, I
AF: Space and Atmos. Phys. Group, Imperial College, London, W1P 7PP United Kingdom
AU: Ledvina, S A
AF: Space Science Lab, Univ. of California, Berkeley, CA 94720 United States
AU: De La Haye, V
AF: Dept. of Atmos., Oceanic,and Space Sci., University of Michigan , Ann Arbor, MI 48109 United States
AB: The Ion and Neutral Mass Spectrometer (INMS) instrument onboard the Cassini Orbiter jettisoned its cover and started making measurements shortly after the spacecraft's main engine shut off. The mass spectra obtained with the INMS open source ion mode when the spacecraft was over the A-ring showed clear peaks at mass numbers associated with O2+, O+, and H+ ions. The O2+ peak was by far the largest and suggests the existence of a significant ring-plane ionosphere. The existence of O2+ ions also points to the existence of neutral O2 in the vicinity of the A-ring. This neutral oxygen must then be ionized, perhaps by photoionization by solar ultraviolet photons. Determining absolute ion densities from the INMS data alone is difficult due to the limited INMS field of view but density estimates have been made and can be compared with data from other Cassini plasma instruments. Ring-atmosphere measurements made by INMS in its closed and open source neutral modes appears to be dominated by background signal but possible upper limits to the ring plane neutral density will be briefly discussed.
DE: 5729 Ionospheres (2459)
DE: 6026 Ionospheres--composition and chemistry
DE: 6265 Planetary rings
DE: 6275 Saturn
DE: 2459 Planetary ionospheres (5435, 5729, 6026, 6027, 6028)
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting