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Venus is the closest planet to Earth, getting as close as 38 million km when Venus is at its closest opposition to Earth. In many ways Venus is a twin planet to Earth, similar in size and composition. But then, Venus has many differences as well. Let’s take a look at Earth and Venus.
First, let’s look at the similarities. Earth and Venus are almost identical in size. The diameter of Venus is 12,100 km, which turns out to be 95% the diameter of Earth. Venus has about 82% the mass of Earth. With about the same diameter and roughly the same mass, you would experience approximately the same gravity standing on the surface of Venus. If you could stand on the surface of Venus, you would experience about 91% the pull of gravity you feel on Earth. In other words, if you weigh 100 kg on Earth, you would only be 91 kg on Venus. You would barely notice the difference.
With similar density and mass, scientists think that the internal structure of Venus and Earth are pretty similar. Both planets have a core of liquid metal, a mantle and crust. But a key difference between Earth and Venus is the complete lack of plate tectonics on Venus. In the ancient past, the crust on Venus stopped sliding around and fully solidified. This stopped the carbon cycle; a cycle on Earth that traps excess carbon dioxide inside the Earth.
And without an active carbon cycle, Venus experienced a runaway greenhouse effect. Air pressure on the surface of Venus is 92 times the pressure on Earth. This thick carbon dioxide atmosphere traps heat from the Sun, and has caused temperatures on the planet to soar to 735 Kelvin (461 degrees Celsius). This makes Venus the hottest planet in the Solar System – even hotter than Mercury. Scientists think that Venus might have look similar to Earth in the distant past, with liquid water on the surface, but it’s all gone now.
While the atmosphere on Earth has a nice breathable mixture of oxygen and nitrogen, the atmosphere on Venus can only be described as hellish. The temperatures are hot enough to melt lead, and consist of almost 97% carbon dioxide.
Finally, Earth has a Moon, while Venus has no moons at all. It’s possible that Venus had moons in the past, but they were either torn away or crashed onto the surface of the planet billions of years ago.
We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.