You might be surprised to know that Venus is the hottest planet in the Solar System. With a global temperature of 735 Kelvin (462 degrees C), the surface of Venus is hot enough to melt lead. And if you could stand on the surface of Venus, you would experience atmospheric pressure 92 times greater than what you’re used to on Earth. Why is Venus so hot? The Venus greenhouse effect shows you what happens when this the process of trapping sunlight goes out of control into a runaway process.
As you probably know, carbon dioxide is a greenhouse gas. Various wavelengths can pass through this invisible gas, but it’s very effective at trapping heat. Light from the Sun strikes the ground of Venus, and warms it up. The ground tries to radiate heat back into space but the carbon dioxide traps much of it around the planet keeping it so warm. This is the same thing that happens when you keep your car windows closed on a hot day.
Scientists think that Venus used to be more similar to Earth, with lower temperatures and even liquid water on the surface of the planet. At some point, billions of years ago, the planet started to heat up. At some point, all the water on the surface evaporated into the atmosphere. Water vapor is an even more powerful greenhouse gas than carbon dioxide and this caused temperatures to rise even more. Then the surface of Venus got so hot that the carbon trapped in rocks sublimated into the atmosphere and mixed with oxygen to form even more carbon dioxide. And so today we have a carbon dioxide atmosphere on Venus which is 92 times more dense than Earth’s atmosphere at the surface.
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Could this happen on Earth? Scientists think that if the same process happened on Earth, we would have temperatures with several hundred degrees C, and an atmosphere 100 times as dense as we have right now.
We have written articles on Universe Today about the Venus greenhouse effect. Here’s an article about the planet’s evolution over time, and here’s an article about how Venus could be colonized with floating cities.
We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.