Satellite Drag Variability at Earth, Mars, and Venus due to Solar Rotation.

Thermosphere densities from precise orbit determination of Mars Global Surveyor, Pioneer Venus Orbiter, and Magellan are used with contemporaneous data from six 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-cm radioflux (used as a proxy for extreme ultraviolet flux) reaching each planet, we find temperature changes of 20.6, 7.0, and 2.0 K for Earth, Mars, and Venus, respectively. The different responses are thought to reflect the differing efficiencies of CO2 cooling and extreme ultraviolet heating in these upper atmospheres, and thus provide an important constraint on planetary atmosphere models that seek to self-consistently and interconsistently simulate the thermospheres of these planets. Our results also provide new data for empirical density models that are used to predict the satellite drag environments of these planets. [ABSTRACT FROM AUTHOR]