The relative proportions of water group ions in Saturn's inner magnetosphere: A preliminary study

Abstract

We present a technique to gather ion composition information in the form of relative abundances of the water group ion species in Saturn's inner magnetosphere, utilizing the Cassini Plasma Spectrometer's Straight-Through Time-of-Flight data from two orbits in 2011. We show that between 4.75 and 8 Saturn radii H₂O⁺ ions dominate the water group species, and from 8 to 10 Saturn radii it is OH⁺ ions that dominate. Our results show that the relative proportion of H₃O⁺ falls fastest with increasing distance, while the proportion of H₂O⁺ decreases slowly. However, O⁺ and OH⁺ increase with distance, and O⁺ is the least dominant ion species out to eight Saturn radii outside of which it is comparable to H₃O⁺. The relative abundance of H₂O⁺ found here matches theoretical work based on Herschel telescopic data very well. These results are compared with other published work, and further improvements to the technique are discussed.