From Scientific American:

A new study recently accepted in Geophysical Research Letters suggests that not only was Venus habitable in the distant past, it could have remained habitable for billions of years. Michael Way from NASA’s Goddard Institute for Space Studies and his colleagues applied the first three-dimensional climate model—the same computer simulations used to predict human-caused climate change on Earth—to early Venus. Because previous research only looked at one-dimensional climate models on Venus (which consider incoming and outgoing radiation but do not visualize the complexities, like clouds, within an atmosphere), the results are a huge step forward compared with previous studies, scientists say. “There’s a real difference between a back-of-the-envelope calculation and actually plugging it into a more sophisticated model,” says Jason Barnes, an astronomer from the University of Idaho, who was not involved in the study.

The team first simulated how the Venusian climate might have looked 2.9 billion years ago. Such an ancient date required the researchers to make a few educated guesses about the early planet, such as assuming it had a shallow ocean just 10 percent the volume of that on Earth today. But the results were clear—2.9 billion years ago the second rock from the sun could have had a balmy Earth-like temperature that hovered around 11 degrees Celsius. The team then ran the model for a later Venus some 715 million years ago and found that even under the sun’s heightened heat, the planet would have warmed by only 4 degrees Celsius since that earlier time. Such a slight increase in temperature would have allowed the planet’s liquid ocean to persist for billions of years.

What allowed Venus to stay wet for so long? According to the models, clouds played a key role. They likely piled up on the dayside of the planet, acting as a …

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