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In 2017, astronomers were able to conduct a detailed study of the night side of one of the most dangerous and inhospitable planets in the solar system - Venus. It turned out that the darkness of the night hides mysteries and anomalies that modern science is unable to explain.
Venus is a strange and very dangerous planet. The temperature in some of its regions sometimes reaches 480OС, it rains from the sky from sulfuric acid, and the pressure on its surface is equivalent to the pressure in the depths of the earth's oceans. However, Venus is unique in our solar system for a completely different reason.
A day in this world lasts more than a year: it takes the planet 225 days to fully orbit the sun, while a complete rotation around its own axis takes 243 days. In addition, Venus is the only planet that revolves around a star in the opposite direction to the rotation of other planets.
The mysteries of the night side of Venus
How do these anomalies affect Venus itself? From a human point of view, it is very unfortunate. Due to such a slow rotation, one half of the planet receives a huge dose of solar heat and radiation, until finally it is replaced by the night side.
An international team of scientists, using data from the ESA's Venus Express spacecraft, recently found that there are also very significant differences between the day and night sides of Venus. For the first time in history, astronomers described in detail the night side of the planet, unique cloud structures and even mysterious displacements of the atmospheric layers, which could only be discerned in the darkness of the night.
"Although the atmospheric circulation on the day side of the planet has been studied extensively, there is still a lot to learn about the night side of the planet," says Javier Peralta of the Japan Aerospace Exploration Agency (JAXA) and lead author of the study, published in the journal Nature Astronomy. "We found that the structure of the clouds on the night side is different from that on the day side, and depends a lot on the topography of Venus."
Although the planet itself rotates incredibly slowly, the winds in the Venusian atmosphere blow 60 times faster than this - this phenomenon is called "super rotation". Thanks to such violent winds, clouds on Venus also move in the atmosphere at a high speed, reaching a peak in the highlands (at altitudes from 65 to 72 km).
Studying them was not easy: as you know, the observation of the night side of Venus is complicated by numerous factors. Peralta explains that clouds can only be seen from orbit using their own thermal radiation, but the contrast in infrared images was too low for scientists to make a dynamic map of the atmosphere from them.
As a result, Venus Express used Visible technology and infrared thermal imaging spectrometer (VIRTIS) to take literally hundreds of infrared photographs at various wavelengths, which ultimately allowed the researchers to achieve the desired results.
Stationary waves: abnormal energy flows
This diagram demonstrates the principle of super-rotation in the upper layers of the Venusian atmosphere: on the day side it is more uniform, and on the night side it looks irregular and unpredictable.
Previously, it was assumed that super-rotation occurs uniformly on the day and night sides of the planet. However, new research has shown that the night side of Venus has its own unique cloud formations and a different morphology of the cloud layer in general. Scientists discovered wavy, threadlike clouds, which were simply not there on the day side.In addition, uplifting has been noticed: on Earth, this term means that water layers from the depths of the ocean rise to the surface; in the case of Venus, the same applies to clouds.
This feature of the nighttime half of the planet was dubbed "stationary waves". According to Agustin Sánchez-Lavega of the Universidad del Pais Vasco in Bilbao, Spain, these are a kind of gravitational waves: updrafts that occur in the lower layers of the planet's atmosphere do not follow the rotation of the planet. They are concentrated mostly in the highlands, which suggests that the clouds are directly influenced by topography.
The mysterious waves were modeled in 3D using VIRTIS data as well as radio data from another spacecraft system, the Venus Radio Science experiment (VeRa). Atmospheric waves were thought to be the result of strong winds blowing over topographic features - a similar process has been documented on the daytime side of Venus. However, studies of Russian probes that measured the speed of planetary winds showed that the wind is not strong enough to be the source of such atmospheric anomalies. Moreover, in the southern hemisphere, some of the characteristic features of the landscape are completely absent.
On the night side of Venus, astronomers have discovered mysterious filamentous formations in the atmosphere by studying it with VIRTIS
Even more astronomers were puzzled by the fact that stationary waves are absent in the middle and lower cloud layers of Venus, not appearing below 50 km above the surface. So while science is powerless and unable to point out the source of these waves of upward energy.
“When we realized that some of the cloud formations in the VIRTIS images were not moving with the atmosphere, I took my breath away. My colleagues and I argued for a long time about whether we see on the screens - real data or the result of a system error, until finally another team led by Dr. Kuyama discovered the same stationary clouds on the night side of the planet using the NASA Infrared Telescope (IRTF) in Hawaii. In addition, our results were confirmed by JAXA's Akatsuki spacecraft, which detected the largest stationary wave in planetary history as soon as it reached Venus orbit,”Peralta said.
Stationary waves and other planetary night-side anomalies forced scientists to almost completely abandon the earlier models of Venus, so astronomers again had to return to calculations and hastily build new theories that could explain such strange research results.
Perhaps in the future, when research missions gather more information, other secrets of the night side of one of the most inhospitable planets in the solar system will become known.