The red planet is looking a bit less red today, but that might be a good thing. European Space Agency (ESA) scientists operating the Trace Gas Orbiter (TGO) have snapped a photo of Mars with an eerie green glow in its upper atmosphere. This effect, known as night glow, is caused by oxygen atoms interacting with solar radiation, and its presence on Mars could help us understand certain aspects of physics.
It’s likely you’ve seen images and even video featuring night glow, but not on Mars. Earth exhibits the same green light in the atmosphere. Night glow is extremely hard to see from the surface of Earth, but there are numerous images from the International Space Station and satellites that show the wispy green light. The process that generates night glow is similar to auroras like the northern lights. As charged particles from the sun impact the atmosphere, they excite atoms in the atmosphere, causing them to emit light at particular wavelengths. The difference with night glow is that it’s a continuous, subtle glow visible in more areas. There’s also a daytime component fittingly called day glow, but that’s even harder to spot.
While Mars has virtually no breathable oxygen, there are plenty of oxygen atoms in the form of carbon dioxide. This new observation of Mars is the first time we’ve ever seen night glow anyplace other than Earth. As with Earth, the European Space Agency team operating the TGO suspected the glow would only be visible edge-on. So, they oriented the satellite to scan between 12 miles and 250 miles (20 to 400 kilometers) above the surface. Sure enough, they saw the characteristic green glow of oxygen.
The team created models to better understand what’s going on in the Martian atmosphere. The glow is most likely a result of carbon dioxide breaking apart in the upper atmosphere, leaving enough free oxygen to produce light. TGO analyzed the light from these atoms in the visual spectrum and ultraviolet, and the visible output was 16.5 times higher than UV. Surprisingly, night glow emissions on Earth are weaker than on Mars, which suggests there is still more to learn about how oxygen atoms behave under extreme conditions.
The Trace Gas Orbiter arrived at mars in 2016 as part of the ExoMars mission. The Schiaparelli lander sadly malfunctioned during its descent and crashed into the surface. The next phase of ExoMars has been delayed and missed its 2020 launch window. The 2022 launch will include a stationary lander and the Rosalind Franklin rover.
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