For the first time, oxygen atoms have been detected in the dayside atmosphere of Venus without being part of larger molecules. Although oxygen has previously been observed on Venus’ night side, the same study found it to be far more widespread than previously observed. The findings are considered a step towards the future missions to Venus that are now increasingly on space agencies’ agendas.
No one doubts Venus has plenty of oxygen in its atmosphere. With oxygen being the third most common element in the universe, we could have confidently predicted its presence there before the first spacecraft flew by. When those missions did investigate Venus at close range, they revealed an atmosphere laden with carbon dioxide and carbon monoxide (CO2 and CO), whose names alone make clear the oxygen contribution.
However, oxygen is an extremely reactive element, so on planets, it usually binds to other elements in the crust or atmosphere. Consequently, the presence of atomic oxygen is far from a given. Nevertheless, observations of Venus’ atmosphere by the Venus Express satellite have previously revealed some atomic oxygen glowing on its night side. Newly published observations not only show oxygen is much more prevalent than that, but also offer some insight into the processes that create and distribute it.
Professor Heinz-Wilhelm Hübers of the German Aerospace Center and colleagues used the Stratospheric Observatory for Infrared Astronomy (SOFIA) to look for oxygen in Venus’ upper atmosphere at 17 locations and found it at all of them.
The oxygen is formed through sunlight breaking up CO2 and CO molecules. The powerful Venusian winds sweep the atoms to the night side, where they combine into molecular oxygen (O2, like in our atmosphere), before reacting with other elements. Despite this redistribution, oxygen densities are up to five times higher on the dayside than the night.
According to the team, atomic oxygen is abundant enough to play an important role in the atmosphere. When an oxygen atom strikes a carbon dioxide molecule, it gives the molecule energy that is then radiated away at 15 micrometers. This is the dominant cooling method in the upper layers of Venus’ atmosphere; the Solar System’s hottest planet would be even hotter without this process.
The atomic oxygen is concentrated at an altitude of around 100 kilometers (60 miles). Earth’s atmosphere is so thin at that point it is often used as the boundary where space is considered to start, but the Venusian atmosphere is much thicker all the way up.
The highest concentrations sit between the two dominant atmospheric circulation patterns, one of which occurs below 70 kilometers (43.5 miles), and the other above 120 kilometers (74.6 miles). Venus turns so slowly – its day is longer than its year – that its high-altitude winds move faster than the rotation of the planet.
The study is published in Nature Communications.