Once upon a time (700 million years ago), in a faraway land (the Solar System), there may have existed a temperate planet hosting liquid water.
A new study by the Goddard Institute for Space Science (GISS) highlights Venus’s climatic history—and its implications for habitability on exoplanets in similar orbits.
Four decades ago, NASA’s Pioneer Venus mission found hints that the world once possessed a shallow ocean’s worth of water.
Now, in an effort to confirm whether Earth’s “twisted sister” ever had a stable climate capable of supporting liquid water, GISS researchers Michael Way and Anthony Del Genio devised a series of simulations.
In all five scenarios—each assuming different levels of water coverage—the pair found that Venus was able to maintain stable temperatures between a maximum of 50 °C (122 °F) for about 3 billion years.
A temperate climate may even have continued today, if not for a series of unfortunate events some 700 to 750 million years ago that caused a release of carbon dioxide stored in the planet’s rocks.
The cause of this “outgassing” remains a mystery; it was probably linked to the planet’s volcanic activity.
“Our hypothesis is that Venus may have had a stable climate for billions of years,” Way said in a statement. “It is possible that the near-global resurfacing event is responsible for its transformation from an Earth-like climate to the hellish hot-house we see today.”
Many scientists believe Venus is beyond the boundary of our Solar System’s habitable zone—not to mention too close to the Sun to support liquid water. But this new study suggests otherwise.
“Venus currently has almost twice the solar radiation that we have at Earth,” according to Way. “However, in all the scenarios we have modelled, we have found that Venus could still support surface temperatures amenable for liquid water.”
This isn’t a definitive answer, though.
According to the Europlanet Society, which published details of the research, there are still two major unknowns that must be addressed:
- How quickly did Venus cool initially? And was it able to condense liquid water on its surface in the first place?
- Was the global resurfacing event a single episode, or the latest in a series of incidents dating back billions of years into Venus’s history?
“We need more missions to study Venus and get a more detailed understanding of its history and evolution,” Way said.
“However, our models show that there is a real possibility that Venus could have been habitable and radically different from the Venus we see today,” he continued. “This opens up all kinds of implications for exoplanets found in what is called the ‘Venus Zone,’ which may in fact host liquid water and temperate climates.”
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