Venus – a hellish planet with an atmosphere of carbon dioxide, almost no water and temperatures of more than 460 degrees Celsius – may once have been habitable, according to Nasa scientists.
Researchers used climate models to calculate that Venus might have had a shallow ocean of liquid water and temperatures that could have allowed life to exist for up to two billion years of its early history.
The atmosphere is 90 times as thick as the air on Earth and scientists had thought this was largely caused by the difference between the two planets’ rate of spin.
A day on Venus lasts 117 Earth days because it spins on its axis at a much slower rate. But recent research showed that Venus could have had an atmosphere similar to the Earth’s today.
The first signs that Venus once had an ocean were discovered by NASA’s Pioneer mission in the 1980s.
Venus is closer to the sun than Earth and receives far more sunlight.
This caused the ocean to evaporate, water-vapour molecules were broken apart into hydrogen and oxygen by ultraviolet radiation and the hydrogen escaped to space.
With no water left on the surface, carbon dioxide built up in the atmosphere and led to a runaway greenhouse gas effect that created present searing heat.
Michael Way, a researcher at Nasa’s Goddard Institute for Space Studies (GISS) in New York, said: “Many of the same tools we use to model climate change on Earth can be adapted to study climates on other planets, both past and present.
Colleague Anthony Del Genio added: “In the GISS model’s simulation, Venus’ slow spin exposes its dayside to the sun for almost two months at a time.
In a statement, Nasa said it was thought that Venus may have had more land than Earth. One of the factors they had to take into consideration was the ancient sun was up to 30 per cent dimmer.
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