A new spiral model for Saturn's magnetosphere

Abstract

Rather than a clock-like strobe, a rotating spiral may underlie the ~10.7 h periodicities observed in many phenomena in Saturn's magnetosphere. This spiral is a density or flux wave propagating outward from the planet, and the periodicity is generated when a spacecraft encounters the wave. The wave moves outward with the Alfvén speed, which can be computed from the magnetic field strength and plasma mass density. Using data from the first 200 days of 2010, the observed field strength and plasma density are used to compute this speed and construct the spiral. When the Cassini spacecraft "flies through" this model on a real trajectory, the model produces a strong main period at 10.7 h with weaker secondary periods at 10.4 h and 11.0 h resulting from Doppler effects. Periodograms of observed phenomena from the same interval show a main peak at 10.7 h but with spurious secondary peaks due to noise.