Mars Nightside Electrons Over Strong Crustal Fields

Abstract:

We investigated 7 years worth of data from the electron reflectometer and magnetometer aboard Mars Global Surveyor to explore the photoelectron and solar wind electron populations on the nightside of Mars, over the strong crustal field region located in the southern hemisphere. Just under 600,000 time data points, each including energy and pitch angle distributions, were examined. Before solar zenith angle of 110$\degree$, photoelectrons have the highest occurrence rate; beyond that, plasma voids occur most often. Once past solar zenith angle of 110$\degree$, energy deposition of electrons happens mainly on vertical field lines with median pitch angle averaged energy flux values of 10$^7$-10$^8$ eV cm$^{-2}$ s$^{-1}$. Fractional deposition rates were examined and the highest found was 0.16, which means that the majority of precipitated electrons are magnetically reflected or scattered back out. The average energy of the deposited electrons is found to be 15-30 eV, typical energies of photoelectrons and unaccelerated solar wind electrons. Lastly, deposited flux values were used to look into auroral excitation and ionization. Median electron flux values, from near vertical magnetic field lines past solar zenith angle of 110$\degree$, calculated in this study produced a total electron content of 4.2 $\times$ 10$^{14}$ m$^{-2}$ and a corresponding peak density of 4.2 $\times$ 10$^3$ cm$^{-3}$.