Venus has oxygen all over

Venus’s atmosphere is almost entirely made up of carbon dioxide – but German astronomers have detected oxygen in the planet’s atmosphere on both its day and night sides.

The discovery could shed light on why the Venusian atmosphere is so different to our own. It may also help support future space missions to Venus.

Earth’s nearest neighbour in the solar system, Venus is also nearly identical in size to Earth (our planet has a radius of 6,371 km, Venus 6,052 km). Earth and Venus are like twins in the solar system. But Venus could be considered an “evil twin”.

Our hospitable, blue planet is supported by a fresh, oxygen-rich atmosphere. The atmosphere on Venus is about 96% carbon dioxide (CO2), 3.5% molecular nitrogen and trace amounts of other gases including carbon monoxide, sulphur dioxide, water vapour, argon and helium.

It is also the heaviest atmosphere on any of the rocky planets in the solar system, exerting a pressure of 93 bar on the planet’s surface – equivalent to the pressure about 900 metres underwater on Earth.

The conditions on Venus are believed to be the result of a “runaway greenhouse effect.”

Scientists have long theorised that Venus was once much like Earth, even suggesting it once had oceans. But its proximity to the Sun meant that the Venusian oceans evaporated, releasing water vapour into the atmosphere. These molecules were then broken apart by UV radiation, the hydrogen escaped into space and CO2 built up in the atmosphere, leading to Venus’s current conditions.

The authors of the recent study suggest that the oxygen in Venus’s atmosphere is produced on the day side by the breakdown of CO­­2 and carbon monoxide (CO). It is then transported to the nightside by atmospheric circulation.

Venus rotates very slowly. One day on Venus lasts 243 Earth days, while the planet orbits once around the Sun every 225 days, meaning the planet’s day is longer than a year.

Past observations have revealed atomic oxygen (not molecular oxygen, O2) in the night airglow of Venus – a faint emission of light by the planetary atmosphere on planet’s night side. The new study analysed 17 points on both the night and day sides of the planet and found oxygen at all locations.

Measurements were taken using the array spectrometer on board NASA’s Stratospheric Observatory for Infrared Astronomy aeroplane.

The highest concentration of oxygen was found 100 km above the surface of Venus.

The findings are published in Nature Communications.

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