Why Venus Might Have Once Been a Habitable World

Venus is, by all accounts, an absolute hellscape. If you were to land your spaceship there and step outside, you'd be squashed flat by its tremendously heavy atmosphere, choked by toxic gas, and broiled alive by temperatures hot enough to melt lead. So, it's really hard to picture any life thriving there, at least today.

But what about ancient Venus? Billions of years ago, the planet might have hosted oceans on its surface, like present-day Earth (scientists now think that Mars was once wet and blue, too), although any water on Venus has long since boiled away.

In a paper on pre-print server arXiv, which has been submitted to the journal Geophysical Research Letters, scientists argue that young Venus might have been able to support some kind of life. The title of the paper even raises the question of whether it could have been the first habitable world in our solar system—but that's speculative for now.

"We're studying the habitable zones of Earthlike worlds," including those beyond our solar system, in order to figure out where we should be looking for life, author Michael J. Way of the NASA Goddard Institute for Space Studies told me over the phone.

That includes Venus, which is actually so Earthlike—despite the fact that it's blazing-hot and inhospitable to us humans—that it's often called Earth's twin: They're both rocky, they have a similar size and mass, and they're neighbours in our solar system. In the paper, Way and co-authors looked back billions of years ago, to a time when they were more alike.

The scientists created four different scenarios for how climate change might've played out on ancient Venus, by using what happened on Earth as a guide. They plugged in a few different variables, including rotation rates. "We made some assumptions that I think are not unreasonable, and we put them into the model to see if we could give it a more habitable climate," Way told me.

Then they used the models to simulate Venusian evolution.

Two of the simulations produced a version of young Venus that had moderate temperatures, some cloud cover, maybe even occasional snowfall, Way told me. One further suggested conditions that would have allowed for liquid water at the surface over a roughly two billion-year stretch, up until 715 million years ago. (It's worth emphasizing that this research hasn't yet been peer reviewed.)

Meanwhile, at a few points in Earth's ancient history, our planet seems to have been locked up in ice and snow—the so-called "Snowball Earth" hypothesis, Way told me. Venus, which is closer to the Sun, didn't experience these same deep freezes. "That could have influenced the way life evolved over time," if it ever did spring up on Venus, he said. "We didn't mention this in the paper, but it might have changed the ability of life to propagate more quickly."

Scientists actually aren't sure if these "snowball" periods were harmful to early life, or not, Way pointed out. We don't even know where life came from on Earth to begin with, which leaves a lot of questions about how and where (not to mention if) it can be found elsewhere in the universe.

Way hopes this research will help redefine which planets look like possible candidates for life. "This is part of a larger study we're doing," he said.

By stretching our imaginations a little bit, and imagining Venus as different today than it once was a very long time ago, we may come up with some new places to look for life, present-day or ancient.