The European Space Agency's Venus Monitoring Camera, or VMC for short, surprised in the summer of last year what seems to be a bright haze that appeared and disappeared in Venus' atmosphere in a time interval of only a few days. The region where the feature was observed by the VMC is located near the southern areas of Venus, hovered over its upper atmosphere for a couple of days and experienced ever increasing brightness before fading away above the south pole of the planet.

Now, ESA scientists reveal that the haze, with its distinctive dark and bright features, was located over a region of land that was subjected to powerful ultraviolet radiation emitted from the Sun. What happens is that ultraviolet light is absorbed and reflected by the sulfuric acid rich Venusian atmosphere.

However, water vapor and sulfur dioxide gas can be found only in regions of the atmosphere situated well below 70 kilometers, meaning that these particular clouds are supposed to be hidden from exterior view in the visible spectrum, by thick layers of gas located in Venus' dense atmosphere. Alternatively, to explain the weird situation, ESA scientists proposed that sulfuric acid particles are being lifted into the upper layers of the atmosphere along with sulfur dioxide and water vapor, on top the upper layers of the atmosphere, where they are exposed to the powerful ultraviolet emissions coming from the Sun, creating the distinctive bright haze.

Ultraviolet light is powerful enough to break up molecules from gases present in Venus' atmosphere, which can the react relatively easy with each other. The vast majority of these reactions conclude in the creation of sulfuric acid particles.

According to Dmitri Titov of the Max Plank Institute for Solar System Research, the process seems to be relatively similar to that of smog formation on Earth, in heavily polluted areas. On the other hand, the process through which these gases are lifted high up over the upper layers of the Venusian atmosphere still remains a mystery, and is probably a characteristic specific only to its atmosphere. Even more mysterious are the dark features observed in the vicinity of the bright haze, which is believed to be created during ultraviolet light absorption into gas, but what chemical processes determine it is unknown.