Ion Cyclotron Waves in the Saturnian Magnetosphere Associated with Cassini\u27s Engine Exhaust

Five hours after the orbit insertion maneuver that placed Cassini into orbit about Saturn, a long (90 minute) burst of ion cyclotron waves were seen, very different than any waves on the inbound leg of the orbit or on succeeding orbits. The ion cyclotron waves were left-hand elliptically polarized and propagating at a moderately large angle to the local magnetic field. The waves had a noticeable compressional component consistent with their off angle propagation. The frequency band of the signals was moderately broad and consistent with the singly ionized components of the engine exhaust gases: CO2, N2, CO, and H20. While H20 waves are seen elsewhere, and associated with the E ring, these waves were stronger and propagated at a much larger angle to the magnetic field. It appears that the engine exhaust products became ionized by solar EUV and electron impact and then accelerated by the magnetospheric electric field associated with co-rotation. This acceleration produced a ring-beam in velocity space much like that produced by Io pickup ions in the jovian magnetosphere