This false-color composite image of Venus' atmosphere was obtained by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA's Venus Express, from a limb (or profile) perspective.
The top panel shows the oxygen nightglow of Venus at an altitude of approximately 60 miles (96 kilometers) over the surface of the planet, seen at a wavelength of 1.27 microns.
The bottom panel shows the same portion of the atmosphere observed at the same time, but at a different wavelength (around 1.22 microns). Here it is possible to see the nightglow of nitric oxide, which is much weaker than that of oxygen and comes from an higher altitude - around 68 miles (110 kilometers) above the surface.
In red is the thermal emission of Venus at 1.74 microns - one of the atmospheric windows of Venus exploited by VIRTIS.
ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA