OH in Saturn's magnetosphere: Observations and implications

The discovery of OH in Saturn's inner magnetosphere changed our view of this region from one where plasma dominated the physics to one where neutrals are dominant. We revisit Hubble Space Telescope observations of OH and derive revised OH brightnesses for observations in 1992, 1994, and 1995. These OH observations as well as Voyager observations are used as constraints on a model of neutral and plasma interactions. We find that the neutral source required to produce the observed OH brightnesses is 1.4×10²⁷H₂O s^-1, with a sharp peak in the neutral source rate near 4.5 R_S. A good fit to the data requires OH densities of over 700 cm^-3 at 4.5 R_S. Rapid diffusion times, about 5 days at 6 R_S, are required to match the observed ion densities. We find that the plasma and neutral composition vary with distance from Saturn, and make predictions for the ion and neutral densities as a function of radius.