Pickup ions at Dione and Enceladus

Ed Sittler
NASA/GSFC

The icy satellites of Saturn, Dione and Enceladus, have shown from Voyager images to be geologically active and the Cassini Plasma Spectrometer (CAPS) will provide the capability to determine the global composition of these bodies by measuring the pickup ions produced from the ionization of their sputtered atmospheres. We will present our model of their sputtered atmospheres and associated pickup ions and demonstrate CAPS ability to measure these freshly picked up ions from the ambient plasma. These freshly picked up ions are expected to form a ring distribution that will have a uniquely different energy-angle dependence than the ambient plasma ions. In the case of Dione we expect the potential for a strong interaction for which both Voyager and Pioneer spacecraft measured ion cyclotron waves at the Dione L shell. In the case of Enceladus it may be the source of the E-ring and some surprises may be encountered during its close encounter with the Cassini spacecraft. These observations when combined with magnetometer, plasma wave and energetic particle observations will allow us to estimate the source of ions into Saturn's magnetosphere due to these two bodies.