Effect of photo-dissociation on the spreading of OH and O clouds in Saturn's inner magnetosphere

摘要

We examine the contribution of photo-dissociation under quiet solar conditions to the global OH and O distributions in Saturn's inner magnetosphere by performing a Monte Carlo simulation. We first calculate the H _2O distribution generated by H2O sources, namely Enceladus' cryo-volcanic plumes, satellite sputtering, and E ring sputtering. We calculate the OH distribution through photo-dissociation reactions using the calculated H2O distribution and then calculate the O distribution from the obtained H _2O and OH distributions. We quantitatively evaluate the role of the energy increment of produced OH and O particles due to photo-dissociation by comparing the resultant distribution of OH and O particles with and without the energy increment. To quantitatively examine the effect of photo-dissociation on the spreading of OH and O clouds, we use the H _2O model including charge exchange and neutral/neutral collisions based on Cassidy and Johnson (2010), as the initial distribution. For the OH (O) density in the region outside 5 Rs (6 Rs), the density with energy increment is greater than that without energy increment. The contribution of calculated OH density with energy increment to the observation is more than ?10%. The OH ratio outside 6 Rs decreases with radial distance from Saturn. On the other hand, the contribution of calculated O density with energy increment to the observation is less than 10% except for around Enceladus.