It turns out that Venus, surprisingly, sports an ozone layer in its atmosphere just like Earth and Mars do, according to a new discovery made by the European Space Agency's Venus Express spacecraft.

While observing stars at the edge of Venus, the spacecraft noticed the ozone layer through finding the characteristic traces of gases in the atmosphere absorbing starlight at particular wavelengths. The light-absorbing ozone layer was making the distant stars appear fainter than previously thought.

We were surveying the atmosphere of Venus and focusing on other molecules when we stumbled on a very interesting feature in one of the spectra,  said the lead author Franck Montmessin of the LATMOS atmospheric research center in France.

The spectral signature of ozone, a distinctive absorption band at [ultraviolet] wavelengths, was rather pronounced and we could clearly discern it in our plots with the naked eye. 

The ozone layer is estimated to float between 90 and 120 km high in the atmosphere of Venus, and is always confined to a rather thin layer, measuring 5 to10 km across.

The altitude of the ozone on Venus is three to four times higher and its density 1,000 times less than the Earth's ozone layer.

 

This ozone detection tells us a lot about the circulation and the chemistry of Venus's atmosphere, said Hakan Svedhem, ESA Project Scientist for the Venus Express mission. Beyond that, it is yet more evidence of the fundamental similarity between the rocky planets, and shows the importance of studying Venus to understand them all. 

 

Ozone, a molecule consisting of three oxygen atoms, is regarded as a potential biomarker that played an important role in the formation of our planet. Ozone was built up in the Earth's atmosphere around 2.4 billion years ago. The ozone layer in the Earth's atmosphere is known to absorb harmful ultraviolet rays from the Sun. 

The ozone layer on earth was a waste gas emitted from microbes, and also a result of the large quantity of molecular oxygen in the atmosphere, which were broken into atoms upon their exposure to solar ultraviolet rays, forming ozone as the molecules reacted with one another.

 

The simultaneous presence of carbon dioxide, oxygen and ozone in an atmosphere could potentially tell whether a planet supports life.

We can use these new observations to test and refine the scenarios for the detection of life on other worlds, said Montmessin. Though life on Venus is highly unlikely due to its dense atmosphere and hot surfaces, the discovery of a thin layer of ozone is significant, for there is possibility for micro organisms to survive even in a harsh environment like Venus.     

The study was published in the journal Icarus.