HR: 15:25h
AN: P43B-07    [Abstracts]
TI: Neutral Exosphere Densities and Structures at Titan Inferred from Pickup Ions Observed by CAPS
AU: * Hartle, R E
EM: Richard.E.Hartle@nasa.gov
AF: Goddard Space Flight Center, 8800 Greenbelt Road Code 613, Greenbelt, MD 20771 United States
AU: Sittler, E C
EM: edward.c.sittler@nasa.gov
AF: Goddard Space Flight Center, 8800 Greenbelt Road Code 613, Greenbelt, MD 20771 United States
AU: Neubauer, F M
EM: fmneubauer@t-online.de
AF: Institut fur Geophysik und Meteorologie, Universitat zu Koln, Albertus Magnus Platz, Cologne, 50678 Germany
AU: Johnson, R E
EM: rej@virginia.edu
AF: University of Virginia, Engineering Physics, Thornton Hall, Charlottesville, VA 22904 United States
AU: Crary, F
EM: fcrary@swri.edu
AF: Southwest Research Institute, Division of Space Science and Engineering, 6220 Culebra Road, San Antonio, TX 28510 United States
AU: McComas, D J
EM: dmccomas@swri.edu
AF: Southwest Research Institute, Division of Space Science and Engineering, 6220 Culebra Road, San Antonio, TX 28510 United States
AU: Young, D T
EM: dyoung@swri.edu
AF: Southwest Research Institute, Division of Space Science and Engineering, 6220 Culebra Road, San Antonio, TX 28510 United States
AU: Coates, A J
EM: ajc@mssl.ucl.ac.uk
AF: Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Sur RH5 6NT United Kingdom
AU: Simpson, D J
EM: David.G.Simpson@nasa.gov
AF: Goddard Space Flight Center, 8800 Greenbelt Road Code 613, Greenbelt, MD 20771 United States
AU: Bolton, S
EM: scott.j.bolton@jpl.nasa.gov
AF: Southwest Research Institute, Division of Space Science and Engineering, 6220 Culebra Road, San Antonio, TX 28510 United States
AU: Reisenfeld, D
EM: dan.reisenfeld@umontana.edu
AF: University of Montana, Department of Physics and Astronomy, 32 Campus Drive, Missoula, MT 59812 United States
AU: Szego, K
EM: szego@rmki.kfki.hu
AF: KFKI - RMKI, Konkoly Thega Str 29-33, Bldg III, H-1121, Budapest, H-1525 Hungary
AU: Berthelier, J
EM: jean-jacques.berthelier@cetp.ipsl.fr
AF: Centre d'etude des Environnements Terrestre et Planetaires, Observatoire de Saint-Maur, 4.Avenue de Neptune, St. Maur-des-Fosses, 94107 France
AB: Measurements of pickup ions, born from neutral exospheres imbedded in moving plasmas, can be used to determine the composition and structure of the parent neutral exosphere constituents [1]. Pickup ions have been observed in Saturn's rotating magnetosphere near Titan by the Cassini Plasma Spectrometer (CAPS) instrument during the Cassini orbiter's recent flybys of the moon. Pickup ions observed by CAPS include H⁺, H₂⁺, N⁺/CH₂⁺, CH₄⁺, and N₂⁺. These ions slow down Saturn's magnetospheric plasma beyond Titan's ionosphere through mass loading. Because of its relatively high mass and high concentration, CH₄⁺ is the dominant mass loading ion. The other ions make negligible contributions to the mass loading process except for N₂⁺ just above the ionopause, where its concentration becomes important. The phase space densities of pickup ions are sensitive functions of the spatial variations of the parent exosphere gasses of the pickup ions [2]. Accounting for such variations, model phase space densities [2], derived from the Vlasov equation, are used in an algorithm to obtain ion density and velocity moments from CAPS measurements. The model implicitly maps an ions trajectory from its observation point to its source point. The analysis shows that because the gyroradius of CH₄⁺ is much greater than the scale height of the source gas, CH₄, the ion fluxes are beamlike with velocities distributed over a narrow range. The observed pickup ion velocities are found to be in ring distributions, with the light ion H⁺ occupying all of its allowed velocities and CH₄⁺ only a small portion of its ring velocities. Applying the algorithm, exosphere densities are inferred. Using CAPS time-of-flight data and empirical cracking patterns, we show that the 14 amu ion is more likely N⁺. We compare ratios of the inferred N and CH₄ exosphere densities with existing exosphere models. 1. Hartle, R. E., K. W. Ogilvie and C. S. Wu, Planet Space Sci., 21, 2181, 1973. 2. Hartle, R. E. and E. C. Sittler, EOS Trans. AGU, 85(17), P33D-04, 2004.
DE: 0328 Exosphere
DE: 2400 IONOSPHERE (6929)
DE: 2455 Particle precipitation
DE: 2732 Magnetosphere interactions with satellites and rings
DE: 6281 Titan
SC: Planetary Sciences [P]
MN: Fall Meeting 2005