Characterization of Foreshock Plasma Populations at Mercury

Abstract

AbstractObservations of foreshock plasma populations at Mercury are presented utilizing measurements from the Fast Imaging Plasma Spectrometer aboard the Mercury Surface, Space Environment, Geochemistry, and Ranging spacecraft. The magnetosphere and foreshock system at Mercury exists in a unique parameter space, due to the planet's relatively weak magnetic dipole and the proximity of its orbit to the Sun. Previous investigations have therefore questioned whether there is sufficient free energy at Mercury to generate foreshock populations, due to the small spatial scale of its bow shock. The observations presented in this work show that field‐aligned beam and diffuse populations similar to those seen in the terrestrial foreshock are able to form upstream of the Hermean bow shock. The observed populations are organized by the bow shock geometry, and are associated with magnetic wave activity previously detected in Mercury's foreshock with corollaries to the terrestrial foreshock.