The discovery by ESA's Venus Express satellite makes Venus only the third planet in our solar system with an ozone layer with Earth and Mars being the others.
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According to the ESA, the build-up of oxygen, and consequently ozone, in Earth's atmosphere began 2.4 billion years ago. "Although the exact reasons for it are not entirely understood, microbes excreting oxygen as a waste gas must have played an important role. Along with plant life, they continue to do so, constantly replenishing Earth's oxygen and ozone," the space agency stated.
Some astrobiologists have suggested that the simultaneous presence of carbon dioxide, oxygen and ozone in an atmosphere could be used to tell whether there could be life on the planet. The findings would let future telescopes target planets around other stars and assess their habitability. However, as these new results highlight, the amount of ozone is crucial, the ESA said.
Theoretical work by astrobiologists suggests that a planet's ozone concentration must be 20% of Earth's value before life should be considered as a cause of its presence. Venus clearly remains below this threshold, the ESA stated.
Venus' ozone layer sits at an altitude of 100 km, about four times higher in the atmosphere than Earth's and is a hundred to a thousand times less dense. According to ESA computer models, the ozone on Venus is formed when sunlight breaks up carbon dioxide molecules, releasing oxygen atoms.
Venus Express made the discovery by using an instrument known as SPICAV (Ultraviolet and Infrared Atmospheric Spectrometer) which analyzes starlight, looking for the characteristic fingerprints of gases in the atmosphere as they absorbed light at specific wavelengths. The ozone was detectable because it absorbed some of the ultraviolet from the starlight, ESA stated.
One big difference stands out however, Venus has very little water. Were the contents of Earth's oceans to be spread evenly across the world, they would create a layer 3 km deep. If you were to condense the amount of water vapor in Venus' atmosphere onto its surface, it would create a global puddle just 3 cm deep. Billions of years ago, however Venus probably had much more water but a large amount has been lost to vaporization into space, the ESA said. If it did have as much water as ESA scientists theorize, Venus it may even have begun its existence as a habitable planet similar to Earth.
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