Martian Electron Foreshock: New Results from MAVEN

Observations upstream from the Martian bow shock obtained by the MAVEN Solar Wind Electron Analyzer (SWEA) experiment are presented. Significant flux enhancements associated with electrons in the energies 50-400 eV range are always observed when MAVEN spacecraft is magnetically connected to the shock. The electron flux reaches a maximum near the shock surface. In addition, electron spikes with energies up to 1.5 keV are also observed near the Martian foreshock boundary. A detailed examination of the pitch angle distribution shows that the enhanced fluxes correspond to electrons moving sunward away from Mars. Also, the full 3-D angular distributions show that the phase space density values are peaked at a non-zero pitch angle and that the electrons appear in a ring centered along the IMF direction. The gyrotropic feature is observed over a large range of the shock geometry from quasi-parallel to quasi-perpendicular. These signatures in the electron distribution function strongly suggest that the reflection off the shock is the main mechanism for the production of Martian foreshock electrons. Although striking differences exist between the Earth and Mars shock structures, these observations show strong similarities in both the Terrestrial and Martian electronic foreshocks.