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Planet Venus may have been habitable for billions of years, says Nasa

Venus may have been warm and wet for billions of years, long enough for life to become established  - Nasa
Venus may have been warm and wet for billions of years, long enough for life to become established - Nasa

The planet Venus may have been habitable for billions of years, Nasa scientists have calculated.

New computer models of the climate history of the second planet from the Sun, show that until around 700 million years ago temperatures ranged from 68F (20C) to 122F (50C), cool enough for liquid water.

In the 1980s, Nasa’s Pioneer Venus mission found hints that the planet once had a shallow ocean, but because it receives far more sunlight than Earth, scientists believed it had quickly evaporated before life could become established.

With no water left on the surface, carbon dioxide rose in the atmosphere, triggering a runaway greenhouse effect that created current conditions.

Today Venus has a crushing carbon dioxide atmosphere 90 times as thick as Earth’s and temperatures at the surface reach 864 degrees Fahrenheit (462C), making life impossible.

Today the surface of Venus is too hot for life - Credit: Nasa
Today the surface of Venus is too hot for life Credit: Nasa

But new computer modelling by Nasa Goddard Institute for Space Science suggests that the ocean may have lasted for two to three billion years.

Not only does it suggest that life could have once evolved on Venus, but it opens up new possibilities about where aliens may exist outside of our Solar System.

“Our hypothesis is that Venus may have had a stable climate for billions of years,” said lead researcher Dr Michael Way.

“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.

“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.”

Images taken by Nasa's Pioneer mission hinted that Venus once had an ocean - Credit: Nasa
Images taken by Nasa's Pioneer mission hinted that Venus once had an ocean Credit: Nasa

At around 4.2 billion years ago, soon after its formation, Venus would have completed a period of rapid cooling and its atmosphere would have been dominated by carbon-dioxide.

If the planet evolved in an Earth-like way over the next 3 billion years, the carbon dioxide would have been drawn down by rocks and locked into the surface.

By around 715 million years ago, the atmosphere would have been dominated by nitrogen with trace amounts of carbon dioxide and methane – similar to the Earth’s today – and these conditions could have remained stable up until present times.

However Dr Way believes that intense volcanic activity around 700 million years ago transformed Venus. One possibility is that large amounts of magma bubbled up, releasing carbon dioxide from molten rocks into the atmosphere.

The magma solidified before reaching the surface and this created a barrier that meant that the gas could not be reabsorbed, causing runaway global warming.

Most researchers believe that Venus is beyond the inner boundary of our Solar System’s habitable zone and is too close to the Sun to support liquid water. But the new study suggests that this might not be the case.

“Venus currently has almost twice the solar radiation that we have at Earth. However, in all the scenarios we have modelled, we have found that Venus could still support surface temperatures amenable for liquid water,” said Dr Way.

The research was presented at the European Planetary Science Congress.