Electron trapping in the coma of a weakly outgassing comet

Abstract

Measurements from the Rosetta mission have shown a multitude of nonthermal electron distributions in the cometary environment, challenging the previously assumed plasma interaction mechanisms near a cometary nucleus. In this paper, we discuss electron trapping near a weakly outgassing comet from a fully kinetic (particle-in-cell) perspective. Using the electromagnetic fields derived from the simulation, we characterize the trajectories of trapped electrons in the potential well surrounding the cometary nucleus and identify the distinguishing features in their respective velocity and pitch angle distributions. Our analysis allows us to define a clear boundary in velocity phase space between the distributions of trapped and passing electrons.