For decades, scientists have held onto the idea that Venus may be home to alien life.
But a new study has dashed those hopes – as scientists claim that Earth’s ‘evil twin’ has never had liquid water on its surface.
By studying the composition of the planet’s atmosphere, researchers from the University of Cambridge found that Venus has likely been dry for its entire history.
Without liquid water, it is almost impossible that life as we know it could have formed on the planet.
This discovery suggests that Venus may be at the very limit of the sun’s habitable zone, narrowing down the area in which life as we know it could be found.
However, the researchers say that the search for life on Venus is not necessarily over.
Lead researcher Tereza Constantinou, a PhD student at the University of Cambridge, told MailOnline: ‘While this rules out Earth-like life, it leaves open the intriguing possibility of extreme, unconventional life forms thriving in Venus’s hostile cloud environment.
‘Any potential life in the Venusian clouds would have originated and evolved under entirely different conditions, perhaps adapted to survive in sulfuric acid clouds — so very much life as we do not know it.’
Scientists have dashed hopes that Venus (pictured) might be home to alien life as a new study shows that the planet has always been dry and inhabitable
Venus is the closest planet to Earth and is only 24 million miles closer to the sun. Venus and Earth are often called ‘sister planets’ due to their similarities in mass, size, and density but have evolved very differently
Venus and Earth are often called ‘sister planets’ due to their similarities in mass, size, density, and distance from the sun.
Yet despite their similar origins, the sister planets could not have grown into more different siblings.
While Earth is rich in liquid water and maintains an oxygen-rich atmosphere, Venus is a boiling-hot hell planet.
Ms Constantinou says: ‘Venus now has surface conditions that are extreme compared to Earth, with an atmospheric pressure 90 times greater, surface temperatures soaring to around 460°C (860°F), and a toxic atmosphere mainly composed of carbon dioxide and with sulfuric acid clouds.’
However, based on climate models, scientists believe there are two paths Venus might have taken to end up this way.
In one scenario, Venus began its life rich in liquid water until a runaway greenhouse effect caused by volcanic eruptions led to temperatures spiralling out of control.
In the other, Venus has always been a dry, inhospitable planet and never had the conditions to support liquid water.
In order to investigate which of these stories is more likely, Ms Constantinou and her colleagues looked at the current composition of the Venusian atmosphere.
Scientists believe that Venus could have evolved into its current form (right) in one of two ways. Either it started covered in liquid water oceans (bottom) before a runaway greenhouse effect made it inhospitably hot, or it was always a dry planet (top) as H20 was driven out of the atmosphere into space
The researchers calculated the chemical content of Venus’ volcanic eruptions (illustrated). On Earth, these are 80 per cent water due to the planets high moisture content while those on Venus only contained six per cent water by volume
On any volcanically active planet, the interior and exterior are in a constant state of chemical communication.
Since gases are constantly escaping from the atmosphere into space, these chemicals need to be replaced from within the planet for the atmosphere to remain stable.
When volcanoes erupt they release gases from inside the planet to replace those being lost into space.
This means that by working out how fast chemicals leave the atmosphere and comparing that to the chemicals which remain, astronomers can work out what the conditions inside the planet are like.
On Earth, volcanic eruptions are around 80 per cent steam due to our planet’s water-rich interior.
If Venus had once been covered in oceans, we would expect to see its volcanic eruptions also produce large amounts of water vapour.
However, in their paper published in Nature Astronomy, the researchers found that Venusian eruptions only contain about six per cent water by volume, suggesting that the planet has been dry all along.
This pours cold water on the idea that there might be Earth-like organisms eeking out a precarious living in the Venusian atmosphere.
By looking at the gases in Venus’ atmosphere, researchers predict that the interior of the planet contains low levels of moisture. This suggests that the planet was never home to oceans capable of supporting life. Pictured: A NASA image of the Venusian surface
Ms Constantinou says: ‘One theory for how life may now exist in the clouds, is that it migrated upwards from a once habitable surface.
‘In this scenario, with a warming planet going through a runaway greenhouse effect, as the oceans evaporated and the surface became uninhabitable, life would have migrated to a habitable niche in the clouds.
‘However, the absence of water oceans in Venus’s past suggests Venus never experienced the conditions necessary to develop and sustain Earth-like life — the planet was never habitable.’
These findings contradict some earlier studies which have shown promising suggestions that life may exist on the planet.
For example, this year researchers confirmed traces of ammonia and phosphine in the planet’s clouds – two potential ‘biomarkers’ that are indicative of life.
On Earth, these compounds are produced by the decomposition of organic matter.
Because there are currently no other known natural processes for its production on Venus, it could be being produced by something scientists aren’t aware of.
The ammonia was discovered in the upper reaches of the atmosphere, where it is too cold for life to form.
Although Venus (pictured) was likely to have always been dry, the researchers suggest that some exotic forms of life could have evolved to survive in the clouds of sulphuric acid which make up much of the atmosphere
But some scientists suggest it could have been formed at lower, warmer altitudes before rising to its current position.
However, if Venus really has been dry for its entire history, these biomarkers must have been produced by a non-biological process or by a form of life totally different to that on Earth.
At the end of this decade, NASA’s DAVINCI mission will launch a probe into the Venusian atmosphere to learn more about its chemical composition.
Likewise, the Chinese space program recently announced plans to bring samples of the planet’s atmosphere back to Earth by 2035.
Between them, these two missions could finally settle the question of whether Venus was once wet and habitable or dry and lifeless.
