The flux and source of energetic protons in Saturn's inner magnetosphere

Abstract

The flux of energetic protons in Saturn's inner magnetosphere was observed in two channels from 48–63 and 63–160 MeV. Absorption features caused by the G ring and the satellites Enceladus and Mimas were easily identifiable. The flux observed in the absorption slot of Mimas can be maintained by the decay of a cosmic ray albedo neutron flux of 7×10−3 cm−2 s−1 sr−1. This flux is entirely consistent with calculations of the neutron flux produced by galactic cosmic ray interactions with the rings of Saturn. The omnidirectional proton flux of 8.2×10³ cm−2 s−1 at 2.734 Rs requires a residence time of 30 years. Both the residence time and the energy spectrum are comparable to those found in the inner radiation belt of the earth. The angular distribution is nearly isotropic in the Mimas slot and beyond 4 Rs. Otherwise the pitch angle distribution is pancake and has been approximated by sinn θ with n in the range 2–7. This distribution is consistent with an isotropic neutron source in the ring plane.