Statistical study of electron flux in Martian space environment

The distributions of electrons at different regions in the Martian space environment play a significant role in the planet's evolution. However, the distributions of electrons in the entire Martian space remain unclear. Here, using MAVEN data during 2015～2020, we statistically study the distributions of differential energy fluxes (DEFs) corresponding to electrons in different energy ranges throughout the Martian space environment. Magnetic field and position data are provided by the MAVEN Magnetometer. The MAVEN Solar Wind Electron Analyzer provides the electron differential energy fluxes in the range of 3～5000 eV. Furthermore, the MAVEN Solar Energetic Particle instrument provides the fluxes of energetic electrons from 20 to 1000 keV. All the data are presented in Mars Solar Orbital (MSO) coordinates. We find that the 30～1000 eV electrons are mainly distributed in the induced magnetosheath. For the same energy ranges of the DEFs, the 30～50 eV electron DEFs are significantly lower in the far magnetotail region (−2.8R_M <X_MSO < −2R_M, −1R_M < Y_MSO <1R_M, −1R_M < Z_MSO <1R_M), ~10^6.5 eV/(cm²·s·sr·eV). Throughout the magneto tail, DEFs in the 50～100 eV range are lower. Not only on both sides of the dawn and dusk, but also on the north and south sides, the DEFs in the range of 30～100 eV are symmetrical. The 100～1000 eV electrons are mainly concentrated in the region of −1R_M < Y_MSO < 1R_M, −1.5R_M < Z_MSO < 1.5R_M upstream of the top of the induced magnetosphere, and this distribution feature is most obvious in the range of 100～500 eV electrons. The DEFs of electrons in the 500～1000 eV range are very low in the near-Mars magnetotail region (−2R_M < X_MSO < −1R_M), but increase slightly in parts of the far magnetotail (−2.8R_M < X_MSO < −2R_M). And high energy electrons in the 1000～5000 eV range with DEFs up to 10⁵ eV/(cm²·s·sr·eV) or more occur near the Martian magnetosheath and bow shock, with a small amount in the far magnetotail region (−2.8R_M < X_MSO < −2R_M, −2R_M < Y_MSO < 2R_M, −1R_M < Z_MSO < 1R_M). In these regions, the energetic electron DEFs in the 20～1000 keV range also reach above 10² keV/(cm²·s·sr·keV). But these energetic electrons with DEFs above 10² keV/(cm²·s·sr·keV) have a very discrete distribution in Martian space. Additionally, statistical results show that the increase of partial high-energy electron DEFs in the far magnetotail region (−2.8R_M < X_MSO < −2R_M) is correlated with the local magnetic field strength. In areas with high magnetic field strength, the corresponding 500～5000 eV and 20～1000 keV electron DEFs also increase accordingly. Finally, we discuss possible mechanisms for the excitation of high-energy electrons in the Martian magnetotail and list our statistical conclusions.