Polarization measurements of Saturn Electrostatic Discharges with Cassini/RPWS below a frequency of 2 MHz

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Abstract
Early in 2006 the RPWS (Radio and Plasma Wave Science) instrument and the ISS (Imaging Science Subsystem) onboard the Cassini spacecraft detected a lightning storm on Saturn that lasted for about one month. The RPWS measured the so‐called SEDs (Saturn Electrostatic Discharges), which are high frequency radio signals produced by lightning discharges. The ISS imaged a remarkable cloud system associated with these SEDs at a latitude of 35° South. Below the frequency of 1825 kHz the RPWS was in a mode capable of measuring the polarization of the SEDs. A surprising result was gained; SEDs appeared to be highly polarized (80%) and were exclusively right‐handed polarized with a high degree of circular polarization. We will present an explanation for this diagnosis involving magneto‐ionic modes and their differential absorption in the magnetoplasma of Saturn's ionosphere.

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