Venus is, let's face it, a weirdo. Often called Earth's "twin" due to its size and density, the planet is actually far different from our own.
Venus has a surface air pressure over 90 times that of Earth. If you were lucky enough to spend a day there you would notice that the sun rises in the west and sets in the east, the exact opposite of what you're used to. You would have to be there a long time to witness this – a Venus day is 243 Earth days, slightly longer than its year, which lasts 225 Earth days – which would give you plenty of time to wonder what the hell is going on while being crushed to a pulp by the pressure and incinerated by the 900 degrees Fahrenheit (480 degrees Celsius) temperatures.
So, why does it spin in the opposite direction to every other planet in the solar system?
Well, first off, it's good to know that it really shouldn't. The spin of our planets is believed to have been set as the planets themselves formed from a rotating cloud of gas. Its spin – as well as Uranus's, which spins on its side – is believed to have been altered sometime after this.
In the case of Uranus, the story might be relatively simple. At some point in its past, Uranus took a pounding from a large object, or a number of smaller impacts, bumping it into the tilted rotation we see today.
As for Venus, the same could be possible – one or more objects may have battered it, flipping the planet upside-down from our perspective, or an impact could have slowed and reversed the planet's rotation altogether.
However, there is a slightly more complicated theory: the planet's fast-moving atmosphere interacting with its surface altered its speed and rotation.
"We think of the atmosphere as a thin, almost separate layer on top of a planet that has minimal interaction with the solid planet," Stephen Kane, University of California Riverside astrophysicist said in a press release in April 2022. In a paper, he argued that Venus could be used as a useful analog for exoplanets that are tidally locked, and without the fast, soupy atmosphere of the planet it would be tidally locked to the Sun, just as the Moon is to Earth.
Instead, the atmosphere's interaction with the planet allows it to spin, albeit slowly, and in a way that may explain the increasing rate of rotation that has been observed over the years since its discovery.
"Venus' powerful atmosphere teaches us that it's a much more integrated part of the planet that affects absolutely everything, even how fast the planet rotates," Kane explained.