The Structure and Time Variability of the Ring atmosphere and ionosphere

The Saturnian system is subject to constant bombardment by interplanetary meteoroids and irradiation by solar UV photons. Both effects release neutral molecules from the icy ring particles either in the form of impact water vapor or gas emission in the form of H2O, O2 and H2. The SOI observations of the Cassini spacecraft have shown the existence of molecular and atomic oxygen ions. Subsequent modeling efforts have led to the picture that an exospheric population of neutral oxygen molecules is maintained in the vicinity of the rings via photosputering and other means. At the same time, the ring system is embedded in a system of O+ and O2+ ions threading through the Cassini division. Charge exchange and collisional interactions between the exospheric ions and neutrals will create a scattered component of O2 molecules (and O atoms) which can be injected into Saturn's upper atmosphere or the inner magnetosphere. In other words, the ring atmosphere could serve as a source of O2+ ions in Saturn's magnetosphere. The structure of the ring atmosphere/ionosphere complex and the injection rate of O2+ ions are, however, subject to modulation by the seasonal variation of Saturn along its orbit. In this work, we will demonstrate how the physical properties of the ring oxygen atmosphere and the scattered component (and the source rate of the magnetospheric O2+ ions) would vary as the ring system going through the cycle of solar insolation.