Glowing oxygen atoms give the red planet’s atmosphere a green touch.
The atmospheres of planets glow constantly both at night and during the day, as sunlight interacts with atoms and molecules found in the atmosphere. Because the green glow that so creates at night, for example, is quite weak, it is best seen when you look at it from the side, for example from the ISS. And astronauts have spotted this spectacular night glow many times.
Detecting this glow around planets other than Earth is a lot harder. Still, the Trace Gas Orbiter has now managed to detect the glow. “One of the brightest emissions we can see on Earth is caused by the night glow or more accurately because oxygen atoms emit light at a very specific wavelength,” said researcher Jean-Claude Gérard. Researchers have suspected for about 40 years that the red planet also has such a green glow caused by oxygen atoms. “And thanks to TGO, we found these,” says researcher Jean-Claude Gérard.
To spot the glow, the researchers focused the necessary instruments on board TGO on the ‘edge’ of Mars. “Similar to the perspective you have on pictures of Earth taken from the ISS,” explains researcher Ann Carine Vandaele.
The researchers studied the Martian atmosphere between April 24 and December 1. They focused on a layer of the atmosphere that is between 20 and 400 kilometers from the Martian surface. It results in a huge dataset, in which that glow popped up every time. “The signal was strongest at an altitude of about 80 kilometers and varied depending on the changing distance between Mars and the sun,” Vandaele explains.
Based on their data, the researchers can also say more about exactly how the glow is created. “We found that it is mainly caused by the disintegration of CO2 into carbon monoxide and oxygen,” says Gérard. “And then we saw the resulting oxygen atoms glow in both visible and ultraviolet light.” However, the oxygen atoms in visible light were found to glow much more intensely than in ultraviolet light. “The observations on Mars correspond to theoretical models, but not to the glow we see around the Earth, where the visible emission is much weaker. This suggests that we need to find out even more about the behavior of oxygen atoms.”
The research provides more insight into the atmosphere of Mars and the processes that play out in this atmosphere – even through the seasons. And that’s important. Not least in view of the various Mars missions planned in the short term, where landers and rovers have to make their way through that atmosphere before arriving on the surface of Mars. “These kinds of observations help us to predict how the Martian atmosphere will react to seasonal changes and variations in solar activity,” said researcher Håkan Svedhem. “Predicting changes in atmospheric density is particularly important for future missions, including the ExoMars 2022 mission in which a rover and a scientific instrument-filled platform are sent to the surface of the red planet.”