Non-detection of Titan lightning radio emissions with RPWS after Cassini's nominal mission

We report on the non-detection of radio emissions associated with possible lightning flashes in Titan's atmosphere by the RPWS (Radio and Plasma Wave Science) instrument onboard Cassini. A valid proof for Titan lightning would be the detection of a number of bursty radio signals above Titan's ionospheric cutoff frequency, and they should be grouped near the closest approach of Cassini to Titan with an approximately quadratic fall-off of signal intensity with spacecraft distance. Such a clear signature has not been detected by the RPWS instrument during the nominal mission of Cassini with 44 close Titan flybys. We emphasize that the interpretation of any bursty signal as being due to a lightning discharge has to be done with the utmost caution. There are examples of spacecraft interferences, Jovian decametric arcs, Solar radio emissions, and enhanced background fluctuations causing bursty lightning-like signals during Cassini's Titan flybys. Similarly, the strong Saturn electrostatic discharges caused by a recent lightning storm located in Saturn's atmosphere were easily detected also at Titan's orbit.