• A. Uranus
  • B. Venus
  • C. Jupiter
  • D. Neptune

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This planet is often called Earth’s ‘sister planet’ because of its similar size, but that’s where the similarity ends. The climate there is far from pleasant, with temperatures hot enough to melt lead.

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The correct answer is B. Venus.

Venus is the only planet in our solar system that has retrograde rotation - in other words, the planet rotates from east to west instead of the other way around like all other planets do. If you look from the sun’s north pole, Venus rotates ‘clockwise’ or ‘to the right’.

The result? On Venus, the sun rises in the west and sets in the east. Completely reversed. And here’s something even stranger: Venus rotates so incredibly slowly on its axis that one day there lasts 243 Earth days. A year on Venus (the time it takes to orbit the sun) lasts only 225 Earth days. Yes, you read that right: a day there lasts longer than a year!

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Why exactly Venus rotates backward is still a mystery that keeps scientists quite busy. The most popular theory involves a gigantic collision early in Venus’s history - something comparable to the impact that probably formed our moon. Such an enormous impact would have had enough force to reverse the entire rotation of the planet.

There’s also a second theory that takes a more subtle approach. It suggests that Venus’s super-thick atmosphere (90 times as dense as Earth’s!) in combination with tidal forces from the sun over billions of years has slowed down and eventually reversed the rotation. That atmosphere, by the way, consists mostly of carbon dioxide, with clouds of sulfuric acid. Doesn’t exactly sound like a pleasant vacation destination.

Uranus is often confused with Venus when it comes to strange rotation, but there’s a different story there. Uranus doesn’t rotate retrograde, but does lie completely on its side with an axial tilt of approximately 98 degrees. As a result, it appears as if the planet rolls along its orbit instead of rotating. That too is probably the result of a collision from the early days of our solar system.

Carl Sagan always talked about Venus as a warning: “Venus is a hellish world where the surface temperature is hot enough to melt lead and the atmospheric pressure is crushing. Yet it reminds us that planets can evolve in dramatically different ways.” He had a point - Venus shows how dramatically different planets can evolve, even if they’re roughly the same size as Earth.

Studying Venus helps scientists understand how collisions, atmospheric processes, and tidal forces can drive a planet’s development. NASA’s VERITAS and ESA’s EnVision missions (planned for the coming years, though these schedules may shift) should hopefully provide more clarity about our mysterious neighboring planet.

Another fun fact: Venus is often called the ‘morning star’ or ‘evening star’. After the moon, it’s the brightest object in our night sky. That brightness comes from the sulfuric acid clouds that reflect no less than 75% of sunlight. So while Venus is a hellish world, it looks beautiful from here.