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After studying the solar system for hundreds of years, you'd think we'd at least have the basics figured out, stuff like why planets spin and orbit the way they do.
Except, we totally don't.
And you only have to look at the planet next door to see it.
When scientists began observing Venus in detail in the 1950s and '60s, they expected it to be pretty unremarkable.
Instead, it turned out to mostly be an inferno of acid rain, one that, of all things, spins backwards!
It's been more than 50 years since then, and while we know a lot more about Venus's climate, we still aren't totally sure why it's rotating the wrong way.
But we at least have some ideas.
In astronomy, a backwards spin is called retrograde rotation, and "backwards" is defined relatively.
Because the solar system formed from one cloud of spinning gas, the planets all orbit in the same direction: counterclockwise, if you're looking down on the Earth's north pole.
