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R.E. Johnson (U.Virgininia), E.C. Sittler (GSFC), F.J. Crary (SWRI), R.L. Tokar (LANL), D. Reisenfeld (U. Montana), T.W. Hill (Rice U.), D.T. Young (SWRI), M.H. Burger (U. Virginia), V.I. Shematovich (Inst. Asatronomy Moscow.), H.T. Smith, M. Michael (U. Virginia), S. Jurac, J.D. Richardson (MIT), R.A. Baragiola (U. Virginia), CAPS Cassini Team
The Cassini Plasma Spectrometer (CAPS) has detected atomic and molecular oxygen and molecular hydrogen ions in the inner magnetosphere and over the icy main rings. The Ion Neutral Mass Spectrometer (INMS) has apparently also seen O2+ (T. Cravens, H. Waite, private communication). O2 can be produced by gas phase processes, but is also a signature of the decomposition of icy objects by radiolysis and photolysis. Therefore, like the observation of an ozone feature on Dione and Rhea, the observation of molecular oxygen ions can be a marker for the radiation-induced erosion of ice grains and icy bodies that orbit within Saturn's magnetosphere. Here we examine the formation and redistribution of molecular oxygen over the icy rings and in the inner magnetosphere and relate to the O atmosphere observed by the UVIS instrument on Cassini.
Thin oxygen atmospheres have been confirmed to be present on Europa and Ganymede formed by radiolysis. Because these bodies have significant gravitational fields, the escape of O2 is inefficient, therefore, Europa has a tenuous molecular oxygen cloud and O2+ has not been clearly detected near the icy satellites. However, radiation induced chemistry on ice grains and small icy bodies in Saturn's system will directly populate the magnetosphere with molecular oxygen leading to the formation of O2+ and its observed dissociation products O and O+.
The presence of O2+ indicates that, in addition to the neutral H, OH, and nitrogen clouds, there is likely a molecular oxygen cloud in Saturn's magnetosphere. Since water vapor can be produced by the incident radiation, by meteoroid impacts, and by collisions between grains and small bodies, the observation of molecular oxygen can be a marker for the charged particle and photo-induced decomposition of ice. Here we present the CAPS data on O2+, O+ and H2+ and calculations of the production of O2 and H2 over the main rings, the tenuous rings and the inner icy satellites. We then describe the redistribution of oxygen in Saturn's magnetosphere by ion molecule reactions and charge exchange.
This work is supported by funding for NASA's Cassini Spacecraft Mission
The author(s) of this abstract have provided an email address for comments about the abstract: rej@virginia.edu
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.