Hello, friends! So I learned a new thing about Mars. Recent research, published just last year in Nature Astronomy, says that the nighttime sky on Mars sometimes glows green. Super bright green. Bright enough that this green glow would be visible to the human eye, if any human eyes were on Mars to see it. According to one source I read, this green Martian airglow would be comparable to “moonlit clouds on Earth.”
So how does this happen? Chemistry! During the day, sunlight zaps carbon dioxide (CO2) gas in Mars’s atmosphere, breaking it up into ionized carbon and oxygen atoms. At night, those ionized oxygen atoms recombine to form molecular oxygen (O2). This specific reaction—the formation of O2—produces a little light in the green and infrared parts of the spectrum. (Please note: I have glossed over an enormous amount of detail here. See the “Want to learn more?” section below for more information).
The infrared glow of O2 formation had been detected previously. A very faint green glow had also been detected over the dayside of Mars. The detection of a green glow at night—that is the new discovery! And also, this green glow is remarkably and astonishingly bright. Brighter, it seems, than anyone expected.
Which initially made me wonder: if this green airglow on Mars is that bright, how did it go undetected for so long? But then again, I sometimes overestimate how much we know about Mars. You’d think we’d know a lot by now. Mars is the second most thoroughly explored planet in the Solar System, after Earth. But in truth, we have just barely scratched the Red Planet’s red surface (and we know even less about all the other planets in our Solar System).
So I see this discovery as a reminder: no matter how much we think we know about space, there is still far, far more we need to learn.
WANT TO LEARN MORE?
This discovery was made by the European Space Agency’s ExoMars Mission, currently in orbit around Mars. Here is a press release from ESA about this discovery.
And here is an article from Universe Today, which goes into more detail about Mars’s airglow, the chemistry behind it, and the way Martian wind patterns and the changing of Martian seasons affect it.
And lastly, for those of you who want to look at the original research, here’s a link to the original research paper from Nature Astronomy (warning: you may encounter a paywall).
Planet Pailly 
Maybe one of the things an astronaut would have mentioned much earlier [?]
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Probably. But we’ve had so many robotic craft operating on or around Mars for so many years now. It still kind of surprised me that something like this could go unnoticed for so long.
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You have to wonder what else we’d learn from an astronaut’s first day on Mars.
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Indeed!!!
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We usually see Mars lit by the sun, so in its daylight. Guess no one’s seen the dark side of Mars until recently.
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True. Very true. But we’ve had orbiters around Mars for a long time now, so I just kind of assumed something like this would have been noticed.
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Naturally this would be advantageous to little green aliens on Mars who are nocturnal.
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Great for camouflage!
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Without having actually read the “Want to learn more” section and without having any expertise in astro-atmospheric-chemistry, I would guess this will stop happening after Mars is terraformed? If it’s CO2, well we have that here but we don’t get a green glow. So maybe it only happens on Mars because of the lack of magnetic field/lack of ozone? Is this similar to the northern lights?
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Actually we do get this here on Earth, but it’s not nearly as bright. You usually can’t see it from the ground, though some photos of Earth from space do show it.
I’m sure the lack of a magnetic field or ozone layer does help. But don’t quote me on that, because I don’t remember reading that in my research.
It is kind of like the northern and southern lights, but it’s also different. Aurora are caused by charged particles getting swept up in Earth’s magnetic field, then directed toward the poles. When those charged particles hit the atmosphere, the collisions produce light. Airglow is caused by chemical reactions happening in the atmosphere.
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This is now my favorite thing about Mars! It sounds very similar to how the Aurora Borealis works on Earth, which also is green thanks to oxygen!
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There are similarities, for sure, though the mechanism causing it is different.
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