Densities of the Venusian thermosphere as revealed by Venus express torque data

The density of the upper thermosphere of Venus was measured in situ using the attitude control system of Venus Express during twelve low-pericentre campaigns between 2008 and 2014. The spacecraft's counteraction to aerodynamic drag torque was used to derive total neutral densities for 91 orbits in the altitude range 160–200 km. The results agree with predictions from the widely used VTS3 model based on Pioneer Venus Orbiter data on the dayside, but shows a much more rapid decrease than expected in density beyond the terminator. Superimposed on the mean density, oscillations consistent with gravity wave activity are observed. The measured wavelengths vary from orbit to orbit, spanning 50–250 km along the spacecraft trajectory, and are present across all sampled latitudes (70°–90°N), solar zenith angles (70°–100°), local times (morning and evening), and altitudes (160–200 km). These results demonstrate that gravity waves are a persistent feature of the Venusian high-latitude thermosphere, providing a pathway for coupling between the lower atmosphere and the upper thermosphere. • Venus thermospheric densities derived from drag torque on Venus Express measured via the attitude control system. • Density profiles agree with VTS3 model on the dayside at 160–200 km, but shows a sharper decrease across the terminator. • Wave activity shows 50–250 km wavelengths with large orbit-to-orbit variation.