Venus is one of the most brutally inhospitable places in our solar system, but many scientists think life may have thrived there at one point. Here's why.
When you look at Venus today, it doesn’t seem like a very welcoming place. With surface temperatures hotter than an oven, atmospheric pressure equivalent to being 3,000 feet deep in the ocean, and no liquid water anywhere that we’ve seen, it seems like the opposite of a comfortable environment in which life could emerge.
A tale of two planets As different as the two planets are today, Venus and Earth were once very similar. The two planets are of similar size, and they formed from similar materials in the earliest stage of the solar system. They are also both within a boundary in the solar system called the snow line, which is the point at which water forms ice grains.
Whether or not there was water there, however, scientists agree that Venus didn’t stay comfortable. At some point, Earth and Venus diverged sharply and Venus entered what is called a runaway greenhouse phase. The higher temperatures caused the surface water to evaporate, forming water vapor in the atmosphere, which was split by sunlight into oxygen and hydrogen, which was then lost into space. Greenhouse gases built up in the atmosphere, raising the temperatures even higher.
The devil is in the timescale It helps to be clear about what we mean when we’re talking about habitability. Because when you hear the word habitable you might think of factors from temperature to radiation amount to oxygen in the atmosphere — all the things that humans need to survive. But in planetary science terms, the word is used in a much more limited way. It refers purely to a planet that has surface temperatures between 0 and 100 degrees Celsius, where water can exist as a liquid.
“The key to habitability is not just achieving the necessary temperature for surface liquid water, but maintaining that,” said Kane. “And maintaining it is the really, really hard part.” “If we’re not getting it right for our solar system, we ain’t getting it right for an exoplanet,” he said.
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