Possible signs of life have been found in the atmosphere of Venus, according to an international team of scientists.
Traces of phosphine, a gas linked to bug-laden swamps on Earth, have been found around 50 kilometres up in the planet’s atmosphere. According to the researchers, the persistence of the gas suggests it is being replenished by some process – and biological activity is the only known explanation.
“We concluded there is no known chemical and physical process that could conceivable produce [the] phosphine,” said team member Dr Janusz Petkowski of the Massachusetts Institute of Technology in America.
“This opens a very rather bold possibility that there might be something living in the clouds of Venus.”
The discovery – made using Earth-bound radio telescopes and reported in Nature Astronomy - has shocked scientists, who have long dismissed Venus – the Earth's nearest neighbour – as utterly inhospitable.
Completely shrouded by a thick atmosphere choked with carbon dioxide and clouds of concentrated sulphuric acid, the surface is hot enough to melt lead. This has led scientists to focus on the search for life on Mars, so far without success.
“This is one of the most exciting signs of the possible presence of life beyond Earth I have ever seen and certainly from the most surprising location I could imagine,” said Prof Alan Duffy, an astronomer from Swinburne University and lead scientist at The Royal Institution of Australia.
“Our twin planet Venus is a hellish world.”
According to Prof Duffy, conditions are less severe high in the atmosphere, and become Earth-like at around 50km – the altitude at which the phosphine was detected. “Something is forming it anew and as phosphine is associated with life on Earth it is tempting to think it could be life on Venus.
“But before we can become more confident about that we have to rule out all possible other non-biological means of producing it.”
Other astronomers also expressed similar excitement over the discovery. "This is huge: it could be the first detection of life beyond Earth,” said Dr Danny Price of the Curtin Institute of Radio Astronomy (CIRA), Australia. “If life can arise in hyperacidic clouds on Venus, it may be that life is widespread across the Galaxy.”
However, Dr Price also stressed the need for caution: “There could be some complex mechanisms replenishing phosphine in the atmosphere of Venus, that we haven't seen happen here on Earth. We need to do intense follow-up observations to provide further evidence.”
How was the discovery made?
A team led by Prof Jane Greaves at Cardiff University, UK were looking for signs of unusual molecules in the atmosphere of Venus using the James Clerk Maxwell radio telescope based in Hawaii. In June 2017 they detected tiny amounts of phosphine, a mixture of phosphorous and hydrogen floating around 50km above the surface of Venus. They then confirmed the discovery using another radio telescope in the Atacama Desert of Chile.
Why the excitement about phosphine?
A toxic, colourless gas, phosphine is also found in trace amounts in the Earth’s atmosphere, and has been linked to swamps – home to so-called anaerobic microbes which do not need oxygen to survive. The discovery of the same gas around Venus has sparked excitement because it should be quickly destroyed by the sulphuric acid in the planet’s atmosphere. This suggests some source of phosphine is continually topping it up. The researchers have investigated a host of possible sources, including volcanoes on the surface of the planet, lightning the atmosphere and even micrometeorites delivering it from space. However, the researchers could find no other source other than biological activity able to produce the levels of gas they observed.
So does that mean life has definitely been found on another planet?
No – and the researchers are keen to stress this. There could be some as-yet unknown chemical process that’s creating the gas. That’s quite likely in the case of Venus, which is a very bizarre place. About the same size as the Earth but closer to the Sun, its intensely hot surface is invisible to ordinary telescopes, and probes that have landed there have been destroyed in hours. Despite various missions to the planet, many mysteries remain about Earth’s nearest neighbour. The researchers also admit the link between phosphine and life is “highly speculative” and raises major technical questions.
Haven’t there been claims like this before?
Yes – about life on Mars. In the mid-1970s, two Nasa probes landed on the surface of the Red Planet with on-board labs designed to test for microbes in the soil. Some of the tests gave positive results, but a panel of experts decided these could have been the result of strange chemical reactions unconnected with life – the very same possibility that could explain the phosphine discovery.
In the mid-1990s, a similar claim was made about the discovery of fossilised life in a meteorite found in Antarctica. Tests showed the meteorite had come from Mars, and a team of Nasa scientists made headlines by claiming to have found a microscopic worm-like fossil trapped within it. Then US president, Bill Clinton, even hailed the potential significance of the discovery. However, the scientific community never accepted the claim, and the consensus is again that some unknown process had fooled the researchers.
What organisms might be creating the gas ?
At best, they are unlikely to be anything more than microbes. Their size is limited by the need to stay aloft in the atmosphere long enough to account for the phosphine. Airborne life is entirely possible: microbes have been found floating through the thin air over 10km above the Earth, and are now thought to play a role in cloud formation. Their Venusian counterparts would also have to survive in clouds of sulphuric acid – but again Earth-bound “acidophilic” microbes have been found that can do this.
What Venusian microbes might consume in order to emit phosphine remains unclear, however.
What happens next?
The research will come under intense scrutiny by other scientists, especially the questionable link between phosphine and living organisms. History also shows that claims about the existence of alien life based just on a failure to find alternative explanations provoke huge scepticism from the scientific community. Even so, the research is likely to prompt a rethink in the quest to find life beyond the Earth – and especially the current focus on Mars. Nasa in particular is likely to dust off plans to revisit Venus and use balloons to study its atmosphere.
Robert Matthews is Visiting Professor of Science at Aston University, Birmingham, UK