A mysteriously fluctuating bulge observed in the atmosphere of Venus already has a clearer explanation. According to a study published in Nature Geoscience, the planet’s huge mountain ranges are to blame for a massive gravity wave.
Venus is often referred to as Earth’s sister planet due to the similarities between the two. However, if it were a twin, it would undoubtedly be an evil one, since its environment is very very different from Earth.
One such difference is a gigantic, 10,000-kilometer-wide arc-shaped structure that travels back and forth in the upper atmosphere of Venus. It was first discovered by the Japanese Venus orbiter Akatsuki in 2015, and it can spend days perfectly still within the turbulent atmosphere of Venus. This lump was most mysterious.
But it is that Venus is peculiar in many ways. It has a retrograde rotation, which means that, like Uranus, it rotates in the opposite direction to the rotation of the Sun, unlike most of the planets in our solar system. It also spins extraordinarily slow: a day on Venus represents about 243 Earth days. That’s many more days than Venus takes to orbit the Sun (about 225 Earth days), so a Venusian day is longer than a Venusian year.
The atmosphere of Venus, however, rotates about 60 times faster than the planet and does one complete revolution once every four days. This disturbing movement causes winds of up to 400 kilometers per hour. The phenomenon is called superrotation , and it appears to preclude the existence of four-day standing gravitational waves, like the massive bulge observed by astronomers.
“During several days of observation, the arc-shaped structure remained relatively fixed in position on the mountain at the surface, despite the background atmospheric superrotation,” the authors comment. “We suggest that the arc-shaped structure is the result of an atmospheric gravity wave generated in the lower atmosphere by the topography of the mountain that then propagates upward.”
To confirm this hypothesis, the scientists created and ran computer simulations of the planet and its atmosphere. And the results of their simulation were in “remarkable agreement with observations over four solar days of Venus from 2015 to 2017.”
Furthermore, the team discovered that these waves could have an effect on the planet’s rotation, causing fluctuations in atmospheric pressure that ultimately slow down the rotation.
This effect lasts for a few minutes per day on Venus, but could help explain previous discrepancies in Venus rotation rate measurements , such as a 2012 ESA study that found a difference of 6.5 minutes compared to one. previous measurement.
Scientists do not know why Venus rotates so slowly or why it is in a retrograde rotation. One of the approaches points to the friction of the dense atmosphere, but there are many things we do not know about Venus and “that we could learn by calculating the exact length of a Venusian day,” according to the team. “An accurate measurement of the length of the day could detect the various impacts of the atmospheric flow against the mountains.”
Once scientists have a more detailed understanding of these mechanisms, they could find a way to explore the interior of the planet, discover the nature of its core, and finally find out what is sustaining the bizarre super-rotation of Venus.
Reference: Atmospheric mountain wave generation on Venus and its influence on the solid planet’s rotation rate. T. Navarro, G. Schubert & S. Lebonnois. Nature Geoscience (2018) DOI: https://doi.org/10.1038/s41561-018-0157-x
