Scientists unravel Venus’ “Y-shaped” cloud mystery

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Scientists have provided deeper insight into the mysteries surrounding the huge “Y-shaped” cloud structure in the atmosphere of Venus and have for the first time succeeded in reproducing its evolution in the course of one month.

The findings are a result of a study led by astronomers from the Institute of Astrophysics of Andalusia (IAA-CSIC), in collaboration with the university of the Basque Country and the Institute of Astrophysics and Space Sciences of Portugal.

Venus is covered by a dense layer of clouds which does not display any noteworthy characteristic. However, when looked in the ultraviolet wavelength, it presents conspicuous dark structures. The biggest one, which practically covers the entire planet, is shaped like a “Y” and it has been a mystery since its discovery more than half a century ago.

When first discovered, astronomers thought the “Y” was simply a group of clouds blown by the wind, but data from mission Mariner 10 (NASA) in 1973 revealed that the structure not only spread like a single entity but also moved at a speed different from its environment.

These dark structures revealed the massive presence of a still unknown compound that absorbs ultraviolet radiation and obscures the region where they get concentrated. Tracking them allowed discovering the “super-rotating” nature of Venus’ atmosphere: while the planet takes 243 days to rotate around its axis, the atmosphere spins around the planet in only four days.

The study by Peralta et al has invalidated the hypothesis, accepted for decades, which assumed that this wave should be one of the types of equatorial waves present on planet Earth.

The researchers have deduced a new type of atmospheric wave compatible with Venus’ extremely slow rotation which explains with striking simplicity the numerous enigmas posed by the “Y”. Its dark color, for example, was due to the fact that the wave pushes upward and concentrates the mysterious ultraviolet absorber.

The wave is confined not only to the equatorial zone but also to the altitudes where the winds reach their highest intensity, what also explains why the “Y” can only be seen on the narrow altitude region of Venus clouds’ tops.

However, the most noticeable achievement of this study has been to prove that the Y shape was due to the distortion that the winds cause on the wave.