资源环境科技发展态势分析平台

Pitch angle distributions (PADs) of very energetic electrons (110-365 keV) are examined during the ring-grazing and proximal orbits of the Cassini spacecraft, from day 320 2016 (15 November) to day 257 2017 (14 September). These repeating orbits allowed a statistical evaluation of the PADs within the magnetopause on the nightside of Saturn. Along L-shells (i.e., equatorial crossing distances of magnetic field lines) near and outside that of Titan and north of the equator, the electron fluxes were unidirectionally field-aligned going away from Saturn. Along L-shells inside Titan's and south of the equator, the electrons had bidirectional or pancake (trapping) PADs. This behavior suggests that the field lines within Titan's L-shell are generally closed, while those outside of that L-shell are generally open. This result strictly applies only to the nightside local times sampled during the final Cassini orbits, but one may infer a similar behavior at other times.