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[19.10] A self-consistent model for Saturn's water cloud and consequences for the Main Rings

S. Jurac, J. D. Richardson (MIT)

We present a model of the plasma and neutral environment which treats plasma and neutrals in the Saturn's magnetosphere self-consistently, constrained by Voyager plasma and H observations and Hubble Space Telescope OH measurements. The neutral distributions are modeled using a Monte Carlo model, and the plasma using a diffusive transport model including sources and losses. We find that the total water source required is 10²⁸ H₂O/s, a factor of 3 larger than previously thought, and that the fraction of molecular ions is larger than in previous work. H₂O is the dominant neutral close to the source region while OH dominantes elsewhere. This dense cloud of water-group neutrals affects the main rings and likely defines the rings' surface composition. The recent Cassini pictures show that the brightness of the main rings increases toward their outer edge, which suggests that this region contains more icy material than the inner portions of the rings. We show that this increased brightness may be a consequence of deposition of water molecules from the surrounding neutral cloud onto the ring particles. We estimate the deposition rates for water-like neutrals onto the ring particles, which are important for determining the surface properties and chemistry of the main rings. The work is supported by NASA Planetary Atmospheres grant to MIT.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.