Robert D. DiFabio
University of Maryland
Spatial and Temporal Variations of the Suprathermal (3-220 keV/e)Ion Composition in Saturn’s Equatorial Magnetosphere
The Cassini spacecraft has been orbiting Saturn since mid-2004 and has greatly improved our understanding of Saturn’s magnetosphere. Unlike Earth’s magnetosphere, Saturn’s magnetosphere is dominated by neutral particles and contains several sources for these neutrals. The moon Enceladus was discovered to have water plumes in its south-pole region making it the dominant source of heavy neutrals. Saturn’s atmosphere, thought to be the strongest source of neutral atomic hydrogen, and Titan’s atmosphere, thought to be the strongest source of neutral molecular hydrogen, are also important. The ionization of these neutral particles provides the majority of the plasma in Saturn’s magnetosphere.
We have studied the suprathermal (3-220 keV/e) ion composition in Saturn’s magnetosphere using data from the Charge-Energy-Mass Spectrometer (CHEMS) on the Cassini spacecraft. We use this data to determine how the suprathermal ion density and composition vary with time, energy, and distance from Saturn (L-shell). This information is used to study the relative importance of various sources of plasma and neutral particles and how they may vary with time. We also examine the loss and energization processes of the suprathermal ions. The water group ions W+ (O+, OH+, H2O+, H3O+) and H+ dominate the ion composition with H2+ being the third most abundant species. He++ and He+ have very low abundances, indicating that the solar wind is a relatively minor source of plasma to Saturn’s magnetosphere.