In some ways, Venus is Earth’s twin – it’s the closest planet to Earth, and it’s almost exactly the same size. But poor Venus flies too close to the Sun. Brighter sunlight and a runaway greenhouse effect makes Venus unbearably hot, with temperatures averaging more than 450 degrees Celsius. But recent climate simulations suggest that Venus wasn’t always a terrifying hellscape. About 750 million years ago, it might have been just as mild and pleasant as Earth!

So how do we know what Venus’ weather was like? Scientists have developed complex computer programs to simulate the Earth’s atmosphere. These models are very useful in forecasting the weather, and also for predicting climate change. Recently, a team of NASA scientists adapted one of these models to look at the weather systems on Venus.

Since Venus is not Earth, the researchers had to make a few changes to the model. First, they increased the power of the Sun. Around 750 million years ago the Sun was not quite as bright, but even then, Venus got a lot more sunlight than Earth does now. They also needed to change the oceans – Venus probably had much less water than Earth. Finally, they changed length of a day. One Venusian day is about 5830 hours long!

When the researchers ran their simulation, an amazing thing happened. One side of the planet – the side in daylight – was covered in cloud, while the other side was clear. The white clouds reflected most of the sunlight back into space, keeping the rest of the planet cool. There was liquid water on the surface of Venus!

Scientists are not certain whether Venus was habitable 750 million years ago. To be sure they would probably need a lander to take rock samples on Venus. But maybe, back before animals emerged from Earth’s oceans, our planet had a twin!

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