Zero Genie

Hellish Venus is as hot as a commercial pizza oven with surface temperatures averaging around 460 degrees Celsius (860 Fahrenheit), far too hot for water or life as it’s known on Earth to exist. But a new study indicates the cloud-shrouded planet may have been a much more temperate – and possibly habitable – world until relatively recent times.

A dramatic transformation starting roughly 700 million years ago resurfaced 80 percent of the planet and triggered a runaway greenhouse effect. But in the two to three billion years leading up to that transformation, computer simulations show Venus could have maintained stable temperatures between 50 C and 20 C (122 and 68 F).

“Our hypothesis is that Venus may have had a stable climate for billions of years,” said Michael Way of the Goddard Institute for Space Science. “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.”

While Venus currently receives almost twice as much solar radiation as Earth, “in all the scenarios we have modelled, we have found that Venus could still support surface temperatures amenable for liquid water.”

Way and his colleague Anthony Del Genio carried out five computer simulations that modelled the consequences of a global ocean averaging 310 metres deep (1,000 feet), a shallow layer of water with an average depth of 10 metres (33 feet) and small amounts of water trapped in Venus’ crust. The simulations included changes in solar energy output as the Sun matured and changes in atmospheric composition.

The researchers simulated the environment 4.2 billion years ago, 715 million ago and today.

About 4.2 billion years ago, Venus would have cooled from the heat of its formation and likely featured an atmosphere dominated by carbon dioxide. Over the next three billion years or so, the carbon dioxide could have been drawn into silicate rocks and effectively removed from the atmosphere.

By 715 million years ago, the simulations show the atmosphere would have been dominated by nitrogen with trace amounts of carbon dioxide and methane. Those conditions could have remained stable until the present, but “something happened on Venus where a huge amount of gas was released into the atmosphere and couldn’t be re-absorbed by the rocks,” Way said.

The probable cause of that outgassing was widespread volcanic activity that released huge amounts of previously trapped carbon dioxide. What caused that transformation remains a mystery. Complicating the question of habitability, researchers need a better understanding of how rapidly Venus cooled and whether water was able to condense on the surface in the first place.

“We need more missions to study Venus and get a more detailed understanding of its history and evolution,” said Way. “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. 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.”