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Science 25 February 2005:
Vol. 307. no. 5713, pp. 1262 - 1266
DOI: 10.1126/science.1106151
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Reports

Composition and Dynamics of Plasma in Saturn's Magnetosphere

D. T. Young,1* J.-J. Berthelier,2 M. Blanc,3 J. L. Burch,1 S. Bolton,4 A. J. Coates,5 F. J. Crary,1 R. Goldstein,1 M. Grande,6 T. W. Hill,7 R. E. Johnson,8 R. A. Baragiola,8 V. Kelha,9 D. J. McComas,1 K. Mursula,10 E. C. Sittler,11 K. R. Svenes,12 K. Szegö,13 P. Tanskanen,10 M. F. Thomsen,14 S. Bakshi,11 B. L. Barraclough,14 Z. Bebesi,13 D. Delapp,14 M. W. Dunlop,6 J. T. Gosling,14 J. D. Furman,1 L. K. Gilbert,5 D. Glenn,11 C. Holmlund,9 J.-M. Illiano,2 G. R. Lewis,5 D. R. Linder,5 S. Maurice,3 H. J. McAndrews,5 B. T. Narheim,12 E. Pallier,3 D. Reisenfeld,14,15 A. M. Rymer,5 H. T. Smith,8 R. L. Tokar,14 J. Vilppola,10 C. Zinsmeyer1

During Cassini's initial orbit, we observed a dynamic magnetosphere composed primarily of a complex mixture of water-derived atomic and molecular ions. We have identified four distinct regions characterized by differences in both bulk plasma properties and ion composition. Protons are the dominant species outside about 9 RS (where RS is the radial distance from the center of Saturn), whereas inside, the plasma consists primarily of a corotating comet-like mix of water-derived ions with ~3% N+. Over the A and B rings, we found an ionosphere in which O2+ and O+ are dominant, which suggests the possible existence of a layer of O2 gas similar to the atmospheres of Europa and Ganymede.

1 Southwest Research Institute, San Antonio, TX 78238, USA.
2 Centre d'Etude des Environnements Terrestre et Planétaires, Observatoire de St. Maur, 94107 St. Maur, France.
3 Observatoire Midi-Pyrenées, 31400 Toulouse, France.
4 Jet Propulsion Laboratory, Pasadena, CA 91109, USA.
5 University College London, Mullard Space Science Laboratory, Holmbury Saint Mary, Dorking, Surrey RH5 6NT, UK.
6 Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK.
7 Department of Physics and Astronomy, Rice University, Houston, TX 77251, USA.
8 Engineering Physics, University of Virginia, Charlottesville, VA 22904, USA.
9 VTT Industrial Systems, 02044, Finland.
10 Department of Physical Sciences, University of Oulu, 90014 Oulu, Finland.
11 Goddard Space Flight Center, Greenbelt, MD 20771, USA.
12 Division for Electronics, Norwegian Defense Research Establishment, N-2027 Kjeller, Norway.
13 KFKI Research Institute for Particle and Nuclear Physics, H-1525 Budapest, Hungary.
14 Space and Atmospheric Science Group, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
15 Department of Physics and Astronomy, University of Montana, Missoula, MT 59812, USA.

* To whom correspondence should be addressed. E-mail: dyoung{at}swri.edu

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