On the neutral cloud distribution in the Saturnian magnetosphere

Recent spectroscopic observations of the saturnian system by the Hubble Space Telescope have shown the surprising results that the icy satellites and the rings are copious sources of neutral gas as a result of magnetospheric particle sputtering and meteoroid bombardment. Not only are the composition and structure of the saturnian magnetosphere significantly influenced by the continuous injection of water-group neutrals and ions, but the dynamics and mass distribution of the main ring as well as the tenuous E ring are also subject to the physical processes occurring in this unique plasma-dust-gas complex. By coupling the orbital motion of the neutral gas cloud with the photochemical effects and plasma chemistry, a numerical scheme is developed to analyze the possible contributions from different source mechanisms to the OH emission detected by the Hubble Space Telescope. It is found that, even if the maximum ion sputtering rate estimated by M. Shi, A. Baragiola, D. E. Grosjean, R. E. Johnson, S. Jurac, and J. Schou (1995, J. Geophys. Res. 100, 26387-26395) is used, the number density of the hydroxyl molecules still falls short by a factor of about 2. The discrepency can be partially elevated if additional source from meteoroid-impact vapor production at Enceladus is introduced. The collisional interaction of Enceladus with the E-ring particles of micron size first proposed by D. P. Hamilton and J. A. Burns (1993, Nature, 365, 498) is of particular promise. One corollary of the present model consideration is that the impact of the E-ring particles in highly eccentric orbits with the A ring could lead to a dense ring atmosphere.