(Venus has ozone layer tooから)
A spacecraft orbiting Venus has discovered an ozone layer high in the planet’s atmosphere, similar to that surrounding Earth and Mars, astronomers say.
ESA’s Venus Express spacecraft made the discovery while watching stars seen right at the edge of the planet set through its atmosphere. Its SPICAV instrument analyzed the starlight, looking for the characteristic fingerprints of gases in the atmosphere as they absorbed light at specific wavelengths.
The finding will help refine searches for life on other planets, astronomers say.
The ozone was detectable because it absorbed some of the ultraviolet from the starlight. Ozone is a molecule containing three oxygen atoms.
According to computer models, the ozone on Venus is formed when sunlight breaks up carbon dioxide molecules, releasing oxygen atoms.
These atoms are then swept around by winds to the nightside of the planet. Here, they can then combine to form two-atom oxygen molecules, but also sometimes three-atom ozone molecules.
The build-up of oxygen, and consequently ozone, in Earth’s atmosphere began 2.4 billion years ago.
Although the exact reasons aren’t entirely understood, microbes excreting oxygen as a waste gas are assumed to have played an important role.