Energetic Particle Signatures of Satellites and Rings in Neptune's Magnetosphere

Abstract

The cosmic ray system on Voyager 2 found a trapped radiation environment in Neptune's inner magnetosphere which is controlled primarily by absorption at the rings and satellite surfaces. The intensity of electrons with kinetic energies ≳ 1 MeV shows particularly strong and narrow signatures associated with absorption by the satellite 1989N1 at an orbital radius of 4.75 Neptune radii. Closer to the planet are several signatures of the inner satellites and rings. Absorption limits the intensity of the inner radiation belt sufficiently for the maximum intensity to occur outside the orbit of 1989N1 at a magnetic L shell of ∼7. Radial profiles of the electron phase space density show that electrons diffuse inward from a source in the outer magnetosphere. Many of the the inward-diffusing electrons are absorbed upon reaching a satellite orbital radius, but the finite absorption efficiency allows some of the electrons to pass by unaffected. The locations of the satellite and ring signatures also provide constraints on the non-dipolar components of the planetary magnetic field.