In recent seasons on Mars, NASA's Curiosity rover has regularly observed translucent clouds in the sky of the Red Planet and the play of colors on them in the rays of the setting sun. When scientists first saw the colorful spots in the photos, they thought they were an image defect. However, testing has shown that at certain times of the day, Martian clouds turn red and green, bringing a little more life to the gloomy sky and desert landscapes of Mars.
An interesting situation also arose when observing night clouds in the sky of Mars. They do not seem to form everywhere and not at all times of the year. For example, the Perseverance rover, which orbits the Jezero crater, has never photographed this phenomenon in four Earth years on Mars. At the same time, the Curiosity rover, located south of the equator, regularly records night clouds. They were previously observed by NASA's Pathfinder mission in 1997 in the northern hemisphere. Apparently, this phenomenon occurs in both hemispheres, but certainly not under all conditions.
Similar clouds also form on Earth, but on Mars they consist mainly of frozen carbon dioxide and only partly of water ice. While Earth's translucent clouds are composed entirely of water ice.
This specificity is noticeable when studying Martian clouds: they are located at an altitude of 60-80 km, and their jets of frozen carbon dioxide can descend to 50 km, where they begin to evaporate. Observing their behavior gives an idea of the size of the particles they are made of and the dynamics of the atmosphere as a whole. The color effects of the setting sun also provide valuable clues about atmospheric processes on Mars.
At the same time, scientists still do not understand why noctilucent clouds are regularly seen in some places on Mars (for example, in the early spring season in the southern hemisphere, where Curiosity operates), but never in other places. On this basis, a hypothesis has emerged that gravitational waves in the planet's atmosphere may be responsible for the formation of translucent clouds on Mars. These are not the waves that arise when neutron stars and black holes collide, but the effect of Mars' gravity on air masses.
It is believed that the zonal action of gravity on cold carbon dioxide in the atmosphere leads to its supercooling, causing it to condense into solid particles and form clouds. While scientists try to unravel the nature of the noctilucent clouds on Mars, we can only admire this rare phenomenon.