Energetic Electron Periodicities During the Cassini Grand Finale

Abstract

AbstractThe Cassini F ring and Proximal orbits took the spacecraft closer to Saturn than any previous mission and allowed determination of energetic charged particles (E > 20 keV) in the inner magnetosphere of the planet. The periodicities of the energetic electrons show a remarkable consistency when analyzed using Lomb periodograms. From the beginning of the F ring orbits in October 2016 to the end of the mission in September 2017, the particles manifest a strong main period of 10.79 h ± 0.01 h, with small Doppler‐related signals slightly above and below this period. The signal‐to‐noise ratio of the main period indicates one of the strongest periods ever seen in Saturn's magnetosphere. As implied by latitude separation, the main period seems to be associated with the northern hemisphere. The 10.79 h period is exactly the same as the single period observed during the early part of the Cassini mission in 2005–6 when Saturn experienced southern summer. A simple rotating searchlight model can simulate the periodograms.