Ion cyclotron waves in Saturn's E ring: Initial Cassini observations

The magnetometer onboard the Cassini spacecraft observes ion cyclotron waves produced by both water‐group (O + , OH + , H 2 O + , or H 3 O + ) and O 2 + ions at nearly all radial distances and local times within the E ring. These left‐hand elliptically polarized waves travel at small angles to the magnetic field and are restricted to near the equatorial plane, where they have their peak amplitudes. They are generated by pickup ions created by the ionization of the neutral exosphere surrounding the E‐ring material, and their subsequent acceleration by the electric field associated with the corotating plasma. The energy flux of these waves is proportional to the energy added to the ions when they are accelerated and enables an estimate of the rate of loss of the ring's exosphere.