The Venus Climate Orbiter, called AKATSUKI, aims to find out why blistering winds zip around the planet at speeds of up to 400 kilometres per hour. The upper clouds can circle the planet in four days or even less, and no one knows why. The effect is called “super-rotation”, because the bulk of the atmosphere is rotating much faster than the planet itself. Venus takes 243 Earth days to make one rotation.

Venus orbiter to fly close to super-rotating wind – space – 14 May 2010 – New Scientist.