The planet Venus has some strange characteristics, but one of its oddest features is its atmosphere. Full of clouds of sulfuric acid, its thick atmosphere hides the surface of the planet and heats it so much that even though it’s further from the sun than Mercury, it is the hottest planet in the solar system. And strangest of all, even though the planet itself rotates slowly, its atmosphere whips around and rotates incredibly fast.
A Venusian day, which is one full rotation of the planet, takes 243 Earth days, but its atmosphere rotates 60 times faster than this, with the top of the clouds rotating all the way around the planet in just four Earth days. And as you look higher in the atmosphere, the rotation becomes faster. This phenomenon, called superrotation, was first discovered in the 1960s but until now, scientists have been puzzled as to what caused it.
Now, a team of astronomers from Japan’s Institute of Space and Astronautical Science have investigated this mystery using data from the Akatsuki spacecraft, also known as the Venus Climate Orbiter. Launched in 2010, Akatsuki was supposed to enter into orbit around Venus in 2010, but had problems and ended up orbiting the sun for five years. But eventually, it managed to enter into a highly elliptical orbit around Venus in 2015, and it has been collecting data about the planet using its cameras ever since.
Akatsuki collects both ultraviolet and infrared images, and it was these which allowed the scientists to see in detail the temperature differences in the atmosphere between the equator and the poles. The warmth of the sun heats the planet’s dayside, creating atmospheric tidal waves due to the temperature difference between the nightside. And these thermal tides push the atmosphere around the planet, making it rotate quickly. But this effect is more pronounced at higher latitudes, as well as being more pronounced at the poles.
So there are two systems at work here to move heat around the planet: One circulation system pushing heat from the equator toward the poles, in addition to the super-rotation which carries heat from the planet’s dayside to its nightside.
These findings aren’t only relevant to Venus, however. They could also be used to understand other exoplanets. “Our study could help better understand atmospheric systems on tidally-locked exo-planets whose one side always facing the central stars, which is similar to Venus having a very long solar day,” lead researcher Takeshi Horinouchi of Hokkaido University said in a statement.
The findings are published in the journal Science.
