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Mars nightside electrons over strong crustal fields
Author(s) -
Shane Alexander D.,
Xu Shaosui,
Liemohn Michael W.,
Mitchell David L.
Publication year - 2016
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021947
Subject(s) - zenith , electron , solar zenith angle , solar wind , physics , photoelectric effect , mars exploration program , pitch angle , flux (metallurgy) , equator , magnetic dip , atomic physics , atmospheric sciences , plasma , computational physics , geophysics , materials science , astronomy , latitude , optics , nuclear physics , metallurgy
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 10 7 –10 8 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 × 10 14 m −2 and a corresponding peak density of 4.2 × 10 3 cm −3 .