Solar Cycle Variability of the Thermospheres of Mars and Earth

This paper comparatively examines long-term variations in the thermospheres of Mars and Earth, from the solar maximum of 2002-2003 to the deep solar minimum of 2009-2010. Data employed include densities and exosphere temperatures derived from orbital drag analyses of the Mars Odyssey (MO) satellite for Mars, and accelerometer measurements on the CHAMP satellite for Earth. Derivation of thermosphere densities are relatively straightforward for Earth, but the Mars thermosphere data require precise orbit determination techniques and separation of such factors as solar radiation pressure and various nuances of the gravity field, as well as accounting for possible density variations connected with dust storms. Delineation of solar cycle variability in planetary thermospheres serves the important role of constraining energetics balances in first-principles general circulation models [1,2,3].