Venus has always been an uninhabitable world, say University of Cambridge astronomers

Cambridge astronomers have found that Venus has never been habitable, after decades of speculation that our closest planetary neighbour was once much more like Earth than it is now.

The University of Cambridge researchers studied the chemical composition of the Venusian atmosphere and inferred that its interior is too dry today for there ever to have been enough water for oceans to exist at its surface. They believe it has been a scorching, inhospitable world for its entire history.

“We won’t know for sure whether Venus can or did support life until we send probes at the end of this decade,” said first author Tereza Constantinou, a PhD student at Cambridge’s Institute of Astronomy. “But given it likely never had oceans, it is hard to imagine Venus ever having supported Earth-like life, which requires liquid water.”

The results, reported in the journal Nature Astronomy, have implications for understanding how unique Earth is and for the search for life on planets outside our Solar System.

Many exoplanets are Venus-like, but the study suggests astronomers should narrow their focus to exoplanets which are more like Earth.

There are two main theories on how conditions on Venus have evolved since its was formed 4.6 billion years ago. One is that surface conditions there were once temperate enough to support liquid water, but a runaway greenhouse effect caused by widespread volcanic activity caused the planet to get hotter and hotter. The other suggests that Venus was born hot and liquid water has never been able to condense at the surface.

“Both of those theories are based on climate models, but we wanted to take a different approach based on observations of Venus’ current atmospheric chemistry,” said Tereza. “To keep the Venusian atmosphere stable, then any chemicals being removed from the atmosphere should also be getting restored to it, since the planet’s interior and exterior are in constant chemical communication with one another.”

When NASA’s DAVINCI mission will be able to confirm whether Venus has always been a dry, inhospitable planet at the end of this decade with a series of flybys and a probe sent to the surface.

The results will help guide the search for planets that can support life in orbit around other stars in the galaxy.

“If Venus was habitable in the past, it would mean other planets we have already found might also be habitable,” said Tereza. “Instruments like the James Webb Space Telescope are best at studying the atmospheres of planets close to their host star, like Venus. But if Venus was never habitable, then it makes Venus-like planets elsewhere less likely candidates for habitable conditions or life.

“We would have loved to find that Venus was once a planet much closer to our own, so it’s kind of sad in a way to find out that it wasn’t, but ultimately it’s more useful to focus the search on planets that are mostly likely to be able to support life – at least life as we know it.”