Venus and Earth are sometimes called twins because they are almost the same size. Venus is almost as big as Earth. They also formed in the same interior of the solar system. In fact, Venus is our closest neighbor to Earth. Therefore, they were formed in the same part of the solar system, from the same materials. They’re about the same size. So you would think they would be very, very similar.

But what happened is that somewhere along the way, they took two very different paths. Some people like to say that Venus is going bad or something is wrong. I like to say that there is something good on Earth somewhere along the way. But what happens on Venus is that the vast, dense atmosphere of carbon dioxide causes the greenhouse effect.

In fact, Venus is hot enough to melt lead. The temperature on Venus’ surface exceeds 900 degrees Fahrenheit, and then Venus is covered by a 15-mile-thick layer of cloud. And these clouds are made of sulfuric acid. So it’s a crazy place but really interesting.

And we really want to understand why Venus and Earth are so different. NASA and ESA kick off the Venus Decade, where we launch three missions together so we can learn more about how Venus formed, how it developed, and why it’s so different from Earth. That’s why he’s sometimes called our evil twin.