Variability of the Satellite Drag Environments of Earth, Mars and Venus due to Rotation of the Sun

Thermosphere densities from precise orbit determination of Mars Global Surveyor (MGS), Pioneer Venus Orbiter (PVO), and Magellan are used with contemporaneous data from 6 Earth-orbiting satellites to investigate the responses of these planetary satellite drag environments to changes in solar flux due to the Sun's rotation. For comparative purposes, these results are cast in the form of equivalent exosphere temperature variations. Per 10-unit change in 10.7-centimeter radio flux (used as a proxy for extreme ultraviolet flux) reaching each planet, we find temperature changes of 20.6 K, 7.0 K and 2.0 K for Earth, Mars, and Venus respectively. The different responses are thought to primarily reflect the differing efficiencies of CO2 cooling in these upper atmospheres, and thus provide an important constraint on planetary atmosphere models that seek to self-consistently and inter-consistently simulate the thermospheres of the planets. Our results also provide new data for empirical density models that are used to predict the satellite drag environments of these planets.