Venus may be enveloped in a thick, choking atmosphere, but this atmosphere is also shrouded in something else: mystery. For the past 50 years, scientists have struggled to explain the presence of a humongous dark structure shaped like a “Y” in the hellish planet’s skies. Now, astronomers believe they have gathered data that could offer an explanation for the mysterious feature’s origins with the discovery of a new type of atmospheric wave in the solar system. The study has been published in Geophysical Research Letters.
When we peer at Venus from Earth, its surface features are obscured by its extremely dense, CO2-rich atmosphere. This thick cloak may seem unremarkable at first glance, but switch to viewing it in UV wavelengths and some interesting features begin to appear. Most notably, a dark Y-shaped cloud structure that virtually wraps around the entire planet can be seen with the stem sitting atop Venus’ equator.
When scientists first spotted this so-called Y feature, they proposed that it was likely just an assemblage of clouds swept up by the wind. However, observations gathered in 1973 suggested something more complex was at play since it not only seemed to be travelling like a single entity, but also moved at a different speed to its environment.
Further observations revealed that the feature’s dark morphology is attributable to the presence of a compound that absorbs UV radiation, although what this is still remains a mystery. By following the movement of the cloud, scientists revealed that the Venusian atmosphere is in a state of “super-rotation” with the atmosphere spinning around the planet in just four Earth days, compared to the 243 it takes to rotate on its axis. With winds travelling at up to 60 times the speed of the planet’s rotation, Venus is the most extreme known case of super-rotation.
Based on these data, scientists speculated that the cloud could be the result of some kind of atmospheric wave or possibly an intermittent change in atmospheric variables, but it was unclear which was more likely. As pointed out by Space.com, in theory, atmospheric waves are capable of producing lots of odd geometric features, such as the hexagon atop Saturn’s North Pole. However, no computer models had managed to reproduce its shape and evolution over time.
Despite a lack of evidence, for many years the prevailing hypothesis was that the Y feature could be the result of a phenomenon we see on Earth known as the Coriolis effect, which is where global wind patterns are deflected on a curved path due to the fact that Earth rotates faster at the equator than the poles. But this explanation was flawed given that the Coriolis effect would be negligible on Venus due to how slowly it spins.
Now, scientists may have finally offered a viable alternative explanation with the identification of a previously unknown type of atmospheric wave that seems to be compatible with the planet’s sluggish rotation. This wave can explain the cloud’s dark coloration as it would drive the unidentified UV absorbing substance upward. Furthermore, the bizarre Y shape can also be explained by the fact that winds cause the wave to become distorted. Between the equator and the middle latitudes, the strong wind that blows westward remains relatively constant. However, at higher latitudes, where the planet’s circumference is smaller, winds whirl around significantly faster and hence distort the wave.
[Via Geophysical Research Letters, Institute of Astrophysics of Andalucia and space.com]