Venus – the hottest planet in the solar system – is harbouring life, according to new research.
It’s not little green men on Mars but the first-ever signs of extra-terrestrial life have been found after a gas produced by microbes was detected.
The ‘aliens’ are believed to be swirling about in clouds 35 miles above the world’s hellish inferno.
Phosphine – the stinkiest gas known to man – has been detected there. It’s given off by anaerobic microbes.
The bugs metabolise their food without the need for air or sunlight. They don’t need oxygen to live and grow – and are still found near hydrothermal vents on Earth.
Learning we are not alone would be the most amazing discovery in history. The British and US team say the evidence is compelling.
They have tried to come up with an alternative explanation for the existence of the volatile fumes – but can’t.
Lead author Professor Jane Greaves, of Cardiff University, said: ” When we got the first hints of phosphine in Venus’ spectrum, it was a shock.”
On Earth, phosphine is considered a conclusive sign of life. It can only be produced by organisms in oxygen-free environments or artificially in labs.
Venus is our closest neighbour – and its surface is scorching and inhospitable with temperatures hot enough to melt lead at 465 degrees celsius.
But hints of the tiny Venusians come from its atmosphere – where the climate can be remarkably temperate and Earth-like. Temperatures range from minus one to 93 degrees celsius.
It’s in this zone phosphine was found – with microbes the only potential source Prof Greaves and colleagues have come up with.
They made the detection using the James Clerk Maxwell Telescope (JCMT) in Hawaii, and the Atacama Large Millimeter Array (ALMA) observatory in Chile.
Co-author Dr Clara Sousa-Silva, a molecular astrophysicist at MIT (Massachusetts Institute of Technology, said: “It’s very hard to prove a negative.
“Now, astronomers will think of all the ways to justify phosphine without life, and I welcome that.
“Please do, because we are at the end of our possibilities to show abiotic processes (not derived from living organisms) that can make phosphine.
“Finding phosphine on Venus was an unexpected bonus. The discovery raises many questions, such as how any organisms could survive.”
On Earth, some microbes can cope with five per cent of acid in their environment. But the clouds of Venus are almost entirely made of acid.
But the researchers considered and tested many methods where the gas might be produced without life – but came up empty-handed.
They included sources on the planet’s surface, small meteorites, lightning or chemical processes happening within the clouds.
Co-author Dr Janusz Petkowski, also from MIT, said: “This means either this is life, or it’s some sort of physical or chemical process that we do not expect to happen on rocky planets.
“We really went through all possible pathways that could produce phosphine on a rocky planet. If this is not life, then our understanding of rocky planets is severely lacking. That’s a pretty definitive statement to make.”
The study published in Nature Astronomy identified a spectral signature – the wavelengths of visible and infra-red light – that is unique to phosphine.
It estimated an abundance of 20 parts-per-billion of the gas in the upper deck of Venus’ clouds – around 33 to 39 miles above the surface.
Prof Greaves said: “In the end, we found both observatories had seen the same thing, faint absorption at the right wavelength to be phosphine gas, where the molecules are backlit by the warmer clouds below.”
Previous research by MIT has shown if phosphine was to ever be found on another rocky planet, it would be a sure sign of life.
Prof Greaves said: “This was an experiment made out of pure curiosity, really, taking advantage of JCMT’s powerful technology, and thinking about future instruments.
“I thought we’d just be able to rule out extreme scenarios – like the clouds being stuffed full of organisms.”
But the opposite occurred – with little Venusians the only ones left standing.
The researchers processed the data for six months before becoming convinced the phosphine was really there.
Co-author Dr Anita Richards, of the UK ALMA Regional Centre and Manchester University, said: “To our great relief, the conditions were good at ALMA for follow-up observations while Venus was at a suitable angle to Earth.
“Processing the data was tricky, though, as ALMA isn’t usually looking for very subtle effects in very bright objects like Venus.”
Co-author Dr William Bains, also at MIT, led the work on trying to assess other natural ways to make phosphine on Venus.
Some ideas included sunlight, minerals blown upwards from the surface, volcanoes, or lightning.
They could only make one ten thousandth of the amount of phosphine the telescopes saw – at most. So something else is producing it, he said.
Co-author Dr Paul Rimmer, of Cambridge University, said terrestrial organisms would only need to work at about ten percent of their maximum productivity to expel the amount found on Venus.
On Earth, anaerobic microbes absorb phosphate minerals – and add hydrogen. Since Venus has virtually no oxygen it suggests the gas really is coming from these types of organisms.
Dr Petkowski said: “This phosphine signal is perfectly positioned where others have conjectured the area could be habitable.”
He added: “You can, in principle, have a life cycle that keeps life in the clouds perpetually. The liquid medium on Venus is not water, as it is on Earth.”
The researchers are now planning to look for other gases that might be associated with life – and see if there are daily or seasonal variations in the signal that would suggest it.
Royal Astronomical Society president Prof Emma Bunce, of Leicester University, who was not involved in the study, is calling for return missions to Venus.
She said: “A key question in science is whether life exists beyond Earth. The discovery by Professor Jane Greaves and her team is a key step forward in that quest.
“I’m particularly delighted to see UK scientists leading such an important breakthrough, something that makes a strong case for a return space mission to Venus.”
Venus – Earth’s closest neighbour – is believed to have been much more habitable a few billion years ago.
It even had oceans before the runaway greenhouse effect took hold.
Dr Sousa-Silva said: “As Venus became less hospitable, life would have had to adapt, It could now be in this narrow envelope of the atmosphere where they can still survive.
“This could show that even a planet at the edge of the habitable zone could have an atmosphere with a local aerial habitable envelope.
“The thick clouds that perpetually cover Venus’ surface are highly acidic, but there is a region where temperatures and pressures are quite Earth-like, making it possible for microorganisms to exist there.”
More than two billion years ago – before Earth was saturated in oxygen – the oceans were filled with anaerobic bacteria – bacteria that metabolise their food without the need for oxygen or sunlight.
The findings will also fuel the theory that life is common throughout the universe.
NASA’s rover Perseverance – due to land on Mars in February – is to dig for signs of ancient microbial life.