Mars nightside electrons over strong crustal fields

We investigated 7 years worth of data from the electron reflectometer and magnetometer aboard Mars Global Surveyor to quantify the deposition of 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 observations, each including energy and pitch angle distributions, were examined. For solar zenith angles (SZA) less than 110°, photoelectrons have the highest occurrence rate; beyond that, plasma voids occur most often. In addition, for SZA >110°, energy deposition of electrons mainly occurs on vertical field lines with median pitch angle averaged energy flux values on the order of 107–108 eV cm−2 s−1. The fraction of downward flux that is deposited at a given location was typically low (16% or smaller), implying that the majority of precipitated electrons are magnetically reflected or scattered back out. The average energy of the deposited electrons is found to be 20–30 eV, comparable to typical energies of photoelectrons and unaccelerated solar wind electrons. Median electron flux values, from near‐vertical magnetic field lines past solar zenith angle of 110°, calculated in this study produced a total electron content of 4.2 × 1014 m−2 and a corresponding peak density of 4.2 × 103 cm−3. Key Points Electron populations on the nightside of Mars are explored Occurrence rates and energy deposition values are calculated Median precipitating flux yields a peak ne of 4.2 × 103 cm−3