Open AccessNightside ionosphere of Mars: Radar soundings by the Mars Express spacecraft
Author(s) -
Němec F.,
Morgan D. D.,
Gurnett D. A.,
Duru F.
Publication year - 2010
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010je003663
Subject(s) - ionosphere , mars exploration program , geophysics , solar zenith angle , physics , zenith , radar , ionospheric sounding , geology , magnetic field , atmospheric sciences , geodesy , astrobiology , aerospace engineering , quantum mechanics , engineering
We present results of a survey of the nightside ionosphere of Mars as observed by Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) on board the Mars Express spacecraft. The occurrence rate of the nightside ionosphere is studied as a function of solar zenith angle (SZA), magnetic field magnitude, and magnetic field inclination. It is shown that at locations with weak crustal magnetic fields the occurrence rate of the nightside ionosphere decreases with increasing SZA up to about 125°, suggesting that plasma transport from the dayside plays a crucial role in its formation. However, at locations with strong crustal magnetic fields, the dependence on SZA is no longer apparent and the inclination of magnetic field becomes a crucial parameter: the occurrence rate of the nightside ionosphere is more than 4 times larger at locations with nearly vertical magnetic fields as compared to the locations with nearly horizontal magnetic fields. This indicates that impact ionization by precipitating electrons is the main ionization source at these locations. Observed peak electron densities are less than 2 × 10 4 cm −3 in the vast majority of cases. Lower estimates of altitudes of peak electron densities are mostly between 100 and 150 km.