Today, our sister planet Venus is a hellish environment, with surface temperatures reaching 450 degrees Celsius and an atmosphere composed of 96% carbon dioxide. However, in a distant period, Venus may have resembled Terra – our hospitable home.
That changed when greenhouse processes, likely triggered by volcanic activity, sent Venus on a trajectory that turned it into the noxious neighbor we know today. But, in recent research that has advanced our understanding of the planet's atmospheric evolution, astronomers have announced the direct detection of atomic oxygen in both the daytime and nighttime parts of the Venusian atmosphere.
Atomic oxygen is the highly reactive chemical cousin of molecular oxygen (the substance we breathe and call simply oxygen). Unlike molecular oxygen, or O2, which is made up of pairs of oxygen atoms, atomic oxygen is made up of individual oxygen atoms.
In short, these individual atoms are always ready to combine with another atom or molecule, which makes atomic oxygen highly reactive – combining would make an oxygen atom more stable, so these singlet oxygens want to react. This is also why molecular oxygen is not as reactive. Its oxygen atoms are already in pairs.
The team of astronomers led by Heinz-Wilhelm Hübers, director of the German Aerospace Center, used the Stratospheric Observatory for Infrared Astronomy (SOFIA) – an airborne observatory – to collect data on the atmosphere of Venus.
"We were able to plan a flight path that allowed us to observe Venus (which is at a low elevation) shortly before sunset for three days, each day for about 20 minutes," Hübers told Space.com. .
On board SOFIA was the heterodyne terahertz spectrometer upGREAT, used for observations. Hübers explained that this spectrometer is particularly sensitive to the frequency and wavelength of atomic oxygen, which are 4.74 terahertz and 63.2 microns, respectively.
Venus' atmosphere is home to two powerful currents. The lower one is below 70 kilometers in altitude, where winds equivalent to hurricane force on Earth blow against the direction of Venus' rotation. The upper current is above 120 kilometers in altitude, with winds flowing in the direction of the planet's rotation.
"A layer of atomic oxygen exists between these two opposing atmospheric currents," says Hübers.
This layer of atomic oxygen, scientists believe, is produced by ultraviolet radiation from the sun, which breaks down carbon dioxide and carbon monoxide in Venus' atmosphere into atomic oxygen and other molecules. In this process, known as photolysis, high-energy photons collide with carbon molecules, essentially forcing them apart.
Since atomic oxygen is predominant concentrated around 100 kilometers in altitude between the two circulation patterns, it is possible that these currents play a role in distributing the substance around the planet. However, Hübers says the team has not been able to quantify this yet with their current measurements.
However, he notes that they observed a local increase in atomic oxygen on the night side of the planet, close to the line that separates day from night, known as the "terminator." Possibly, this increase could be caused by terminator winds.
