Scientists have been looking for a faint green daylight in the atmosphere of Mars for several decades, because this kind of glow should appear with the interaction of sunlight and oxygen.
Of course, such a glow is on Earth, but we have not seen it anywhere else. Forty years ago, it was predicted that such a glow should be on Mars, explains astronomer Jean-Claude Gerard of the University of Liege (Université de Liège, Belgium), the author of a new study.
The discovery of the glow on Mars will help us better understand the processes that lead to its appearance on Earth and on other planets.
The sky of the Earth is never completely black. Even at night. Even if you manage to get rid of light pollution, light of stars and diffused sunlight. The reason is the processes taking place in the atmosphere. The molecules there constantly interact, emitting a faint glow at different wavelengths.
This glow is not just like the northern lights, because the same particles participate in it. But the glow is weaker, and the mechanism of formation is different. Aurora borealis appears when charged particles of sunlight ionize the atoms of the atmosphere.
But the atmosphere’s own glow appears during the interaction of sunlight and the atmosphere. There is a day and night glow. The night was seen not only on Earth, but also on Venus and Mars.
Now, scientists on Mars saw a daylight glow of the atmosphere – a phenomenon that is much more difficult to notice due to the bright light of the Sun.
Earth’s daylight can be seen from the ISS if you point the camera at the horizon, and not strictly down. Scientists decided to try this method on Mars. They turned the NOMAD instrument to the horizon and began to observe the atmosphere of Mars at an altitude of 20 to 400 kilometers.
They saw a glow in both the optical and ultraviolet spectra in all daytime observations. The light was brightest at an altitude of about 80 kilometers. The brightness changed depending on the distance between Mars and the Sun.
Computer modeling has shown that the formation of this natural glow on Mars is similar to the process on Earth. The light of the sun breaks the carbon dioxide molecules in the atmosphere of Mars into carbon monoxide and oxygen. The oxygen atoms give this glow.
It is curious that in the visible range the glow was 16.5 times stronger than in ultraviolet light.
“The observations on Mars coincide with theoretical models, but not with the glow that we see around the Earth, our visible radiation is much weaker,” adds Gerard. It only means that we still have much to learn about how oxygen atoms behave. Perhaps the reason is simply to tune the instruments that observe the Earth’s atmosphere.