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Initial interpretation of Titan plasma interaction as observed by the Cassini plasma spectrometer: Comparisons with Voyager 1 |
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| Authors: | RE Hartle EC Sittler RE Johnson F Crary DT Young D Simpson D Reisenfeld JJ Berthelier J Vilppola N Andre |
| Affiliation: | a NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA b University of Koln, D 50923 Koln, Germany c University of Virginia, Charlottesville, VA 22904, USA d Southwest Research Institute, San Antonio, TX 78228-0510, USA e Mullard Space Flight Center, Dorking, Surrey RH5 6NT, UK f Jet Propulsion Laboratory, Pasadena, CA 91109, USA g University of Montana, Missoula, MT 59812, USA h KFKI-RMKI, KFKI Research Institute for Particle and Nuclear Physics, Budapest H-1525, Hungary i Centre d’etude des Environnements Terrestre et Planetaires, St. maur-des-Fosses, 94107 France j University of Oulu, Linnanmaa, FIN-90014, Finland k Los Alamos National Laboratory, Los Alamos, NM 87545, USA l CESR, Toulouse, 4346 31028, France |
| Abstract: | The Cassini plasma spectrometer (CAPS) instrument made measurements of Titan's plasma environment when the Cassini Orbiter flew through the moon's plasma wake October 26, 2004 (flyby TA). Initial CAPS ion and electron measurements from this encounter will be compared with measurements made by the Voyager 1 plasma science instrument (PLS). The comparisons will be used to evaluate previous interpretations and predictions of the Titan plasma environment that have been made using PLS measurements. The plasma wake trajectories of flyby TA and Voyager 1 are similar because they occurred when Titan was near Saturn's local noon. These similarities make possible direct, meaningful comparisons between the various plasma wake measurements. They lead to the following: (A) The light and heavy ions, H+and N+/O+, were observed by PLS in Saturn's magnetosphere in the vicinity of Titan while the higher mass resolution of CAPS yielded H+ and H2+as the light constituents and O+/CH4+ as the heavy ions. (B) Finite gyroradius effects were apparent in PLS and CAPS measurements of ambient O+ ions as a result of their absorption by Titan's extended atmosphere. (C) The principal pickup ions inferred from both PLS and CAPS measurements are H+, H2+, N+, CH4+ and N2+. (D) The inference that heavy pickup ions, observed by PLS, were in narrow beam distributions was empirically established by the CAPS measurements. (E) Slowing down of the ambient plasma due to pickup ion mass loading was observed by both instruments on the anti-Saturn side of Titan. (F) Strong mass loading just outside the ionotail by a heavy ion such as N2+ is apparent in PLS and CAPS measurements. (G) Except for the expected differences due to the differing trajectories, the magnitudes and structures of the electron densities and temperatures observed by both instruments are similar. The high-energy electron bite-out observed by PLS in the magnetotail is consistent with that observed by CAPS. |
| Keywords: | Titan Plasma Pickup ions Mass loading Composition Cassini |
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