A spacecraft orbiting Venus has discovered an ozone layer high in the planet’s atmosphere, similar to that surrounding Earth and Mars according to astronomers.

The study was recently presented at the Joint Meeting of the European Planetary Science Congress and the American Astronomical Society’s Division for Planetary Sciences.

Franck Montmessin from the Laboratoire Atmospheres, Milieux, Observations Spatiales (LATMOS) in Guyancourt, France, led the team who carried out this study.

While observing stars visible right at the edge of the planet, set through its atmosphere, ESA’s Venus Express spacecraft made the discovery. The SPICAV instrument analyzed the starlight, looking for the characteristic fingerprints of gases in the atmosphere as they absorbed light at specific wavelengths. SPICAV is a remote-sensing spectrometer covering three distinct spectral regions namely ultraviolet, near- and mid-infrared.

Ozone has also been regarded as a potential biomarker, since it traces the distribution of molecular oxygen. The new discovery may help astronomers in their hunt for life on other worlds. Ozone, which was found previously only in the atmospheres of Earth and Mars, is of fundamental importance to life because it absorbs much of the sun’s harmful ultraviolet rays.

About 2.4 billion years ago, the build-up of oxygen and, consequently ozone, began in Earth’s atmosphere. Microbes excreting oxygen as a waste gas are assumed to have played an important role. The Earth's layer of ozone is a result of the large abundance of molecular oxygen in our planet's atmosphere. When irradiated by solar ultraviolet rays, oxygen molecules are broken into atoms, which may, in turn, react with other oxygen molecules and create ozone.

The small amount in Mars' atmosphere is the result of sunlight breaking up carbon dioxide molecules and the same could appear to be true of Venus.

According to the data, ozone is located at varying altitudes in the Venusian atmosphere, between 90 and 120 km, and is always confined to a rather thin layer, measuring 5 to10 km across.

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