Misbehaving High-Energy Electrons: Evidence in Support of Ubiquitous Wave-Particle Interactions on Dayside Martian Closed Crustal Magnetic Fields

Abstract

Multiple studies have reported either isotropic or trapped pitch angle distributions of high-energy (>100 eV) electrons on closed crustal field lines on the dayside of Mars. These pitch angle distributions are not to be expected from collisional scattering and conservation of adiabatic invariants alone. We use 2 years of data from the Mars Atmosphere and Volatile EvolutioN mission to analyze the pitch angle distributions of superthermal electrons on dayside-closed crustal magnetic fields and compare to results from an electron transport model. Low-energy electrons (10–60 eV) have pitch angle distributions in agreement with modeling results, while high-energy electrons (100–500 eV) do not. High-energy electrons have a flux peak at perpendicular pitch angles which suggests there is a ubiquitous energization process occurring on crustal fields. Wave-particle interactions seem to be the most likely candidate. Trapping of high-energy electrons may impact the nightside ionosphere dynamics.