Density profiles of Venus' polar atmosphere
This figure shows the density of Venus' atmosphere in the northern polar regions at altitudes of 130 to 190 km. All data points were gathered during different phases of the Venus Express Atmospheric Drag Experiment (VExADE), performed between 2008-2013 (values above 165 km) and from 24 June to 11 July 2014 (values below 140 km); the black dots to the lower right were from the aerobraking phase (AER), the black dots to the upper left from the Precise Orbit Determination phase (POD), and the grey dots from torque measurements (TRQ).
Each coloured line represents a different scientific model of Venus' atmosphere. The dark blue line shows a model based on data from NASA's Pioneer Venus spacecraft, dubbed VTS3 (Hedin et al., 1983), which uses observations of Venus' equatorial latitudes gathered from 1978-1980 (extrapolated to the poles). The cyan line corresponds to another reference model of Venus' neutral upper atmosphere based on Pioneer Venus, named Venus International Reference Atmosphere (VIRA, Keating et al.,1985). The red line corresponds to a model (Venus Polar Atmosphere Model) currently being developed by Ingo Müller-Wodarg. This model seeks to bridge the data gap shown in the figure from 140-165 km and present a unified vertical density profile for Venus' upper polar atmosphere.