For the first time, scientists have studied clouds and wind on the night side of Venus. And they’ve found that it's very different from the day side.
That data comes from ESA’s Venus Express spacecraft, which entered orbit around Venus in April 2006 before being crashed into the planet in December 2014. Led by the Japan Aerospace Exploration Agency (JAXA), the study was published in Nature.
We already knew that Venus has a weird super-rotation, where its winds can rotate 60 times faster than the planet. But it seems that on the night side, this process is even more chaotic than on the day side.
"This study challenges our current understanding of climate modelling and, specifically, the super-rotation, which is a key phenomenon seen at Venus," said Håkan Svedhem, ESA Project Scientist for Venus Express, in a statement.
The team found that night side clouds form large, irregular patterns, dominated by waves that appear to stand still in the atmosphere, called stationary waves. In January this year, a huge stationary wave was seen on Venus by the Akatsuki spacecraft, stretching for more than 10,000 kilometers (6,200 miles).
In this study, the scientists used data from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) to study the night side, using infrared to study the clouds. They found they did not move with the atmosphere, an unexpected discovery that was later confirmed by Akatsuki.
Stationary waves are thought to form over mountainous or other high-elevation regions. Weirdly though, in this data stationary waves were missing in the intermediate and lower cloud levels, up to about 50 kilometers (31 miles) above the surface.
"We expected to find these waves in the lower levels because we see them in the upper levels, and we thought that they rose up through the cloud from the surface," co-author Ricardo Hueso of the University of the Basque Country in Bilbao, Spain, in the statement. "It's an unexpected result for sure, and we'll all need to revisit our models of Venus to explore its meaning."
Akatsuki is continuing to orbit Venus, so it may be able to shed some light on some of the weird things going on with the planet. With the death of Cassini today, Venus is now one of only three planets aside from Earth – the others being Mars and Jupiter – that have a human spacecraft in orbit.