This image composite shows data on the molecular oxygen (O2) emission in the night-side upper atmosphere of Venus, obtained with data from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA’s Venus Express in May 2006.

Panel a shows the spectra of O2 emission at 1.27-micrometres wavelength. The blue curve corresponds to a region with dominant O2 emission, the green one corresponds to a region intermediate O2 emission, while the red curve corresponds to a region with dominant thermal emission.

Panel b provides a limb, or side image of the upper atmosphere obtained at 1.27 micrometres, showing the an enhancement of the glow at a layer of precise altitude.

Panel c provides a vertical profile of the O2 emission at limb at a latitude of 35°north. The actual, observed profile (red) is compared with simulations from a computer model (blue). From these curves, an average altitude for O2 emission is found to be about 96 km.

This is the first direct measurement of the oxygen nightglow altitude profile.