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Electron impact ionization in the Martian atmosphere: Interplay between scattering and crustal magnetic field effects
Author(s) -
Lillis Robert J.,
Fang Xiaohua
Publication year - 2015
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1002/2015je004841
Subject(s) - ionosphere , mars exploration program , ionization , thermosphere , atmosphere of mars , electron , electron precipitation , physics , atmosphere (unit) , electron ionization , martian , atmospheric sciences , dipole model of the earth's magnetic field , geophysics , magnetic field , computational physics , atomic physics , solar wind , astrobiology , ion , magnetosphere , interplanetary magnetic field , nuclear physics , meteorology , quantum mechanics
Precipitating electrons are typically the dominant source of energy input into Mars' nighttime upper atmosphere, with consequences for atmospheric and ionospheric structure, composition, chemistry, and electrodynamics. Mars' spatially heterogeneous crustal magnetic fields affect the fluxes of precipitating electrons, via both the magnetic mirror force and Gauss' law of conservation of magnetic flux. We use a kinetic electron transport model to examine ionization rate profiles that result from the combination of these magnetic effects and elastic and inelastic scattering by atmospheric neutrals. Specifically, we calculate ionization rates as a function of altitude, crustal magnetic field strength, and the initial energy and pitch angle of the precipitating electrons, covering the relevant ranges of these parameters. Several complex behaviors are exhibited, including bifurcating ionization peaks with distinct characteristics and energy‐dependent and crustal field strength‐dependent increases in ionization with decreasing pitch angle. Elucidating such behavior is important for understanding the effect of Mars' unique crustal fields on the Mars upper atmosphere and ionosphere, both to predict the consequences of measured electron precipitation and to enable, for the first time, downward coupling of global plasma models with thermosphere‐ionosphere models.