The "Airglow" of Venus

New infrared data is now available about Venus’ oxygen airglow – a phenomenon detectable on the night-side that makes the planet glow like a ‘space lantern’.

“The oxygen airglow was first discovered thanks to ground observations, and also observed by other missions to Venus such as the Russian Venera spacecraft and the US Pioneer Venus orbiter,” said Pierre Drossart, co-Principal Investigator on Venus Express’ VIRTIS instrument. “However, the global and detailed view we are getting thanks to Venus Express is truly unprecedented.”

The fluorescence of the airglow is produced when oxygen atoms present in the atmosphere ‘recombine’ into molecular oxygen (or ‘O2’) emitting light. Where does the oxygen come from?
“The oxygen in the atmosphere of Venus is a very rare element,” continued Drossart. At high altitudes in the atmosphere, on the day-side of Venus, the strong flux of ultraviolet radiation coming from the Sun ‘breaks’ the molecules of carbon dioxide (‘CO2’) present in large quantity in the atmosphere, liberating oxygen atoms. “These atoms are then transported by the so-called ‘sub-solar’ and ‘anti-solar’ atmospheric circulation towards the night side of the planet. Here the atoms migrate from the high atmosphere to a lower layer, called ‘mesosphere’, where they recombine into O2. By doing this, they emit light at specific wavelengths that can be observed through remote sensing from Earth and with Venus Express,” added Drossart.
The detection of the airglow, and the capability to follow its evolution in time, is extremely important for several reasons.

“First, we can use the distribution and motion of these fluorescent O2 ‘clouds’ to understand how the atmospheric layers below move and behave,” said Giuseppe Piccioni, the other co-Principal Investigator on VIRTIS. “In this sense, the O2 airglow is a real ‘tracer’ of the atmospheric dynamics on Venus.”

“Second, the analysis of this phenomenon will provide new clues on how its global atmospheric chemistry works – a very challenging task indeed, and still an open field of research,” continued Piccioni. “By calculating the speed at which this chemical ‘recombination’ takes place, we might be able – in the future – to understand if there are mechanisms that favour, or catalyze, this recombination, and learn more about the production and recombination of the other chemical species in the Venusian atmosphere.”

“Third, the observation of the oxygen airglow also allows to a better understanding of the global ‘energetic’ exchange between Venus’s mesosphere – at upper boundary of which the airglow is situated, with Venus’ thermosphere, an even higher layer directly influenced by the Sun.”