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Traces of pungent gas floating through the clouds of Venus may be emanations from airborne organisms – microbial life, but not as we know it.
Astronomers detected phosphine 30 miles up in the planet’s atmosphere and failed to identify a process other than life that could explain its presence.
The discovery raises the possibility that life took hold in Earth’s inner neighbor and the remnants clung to, or at least floated, while Venus underwent runaway global warming that turned the planet into hell.
For 2 billion years, Venus was temperate and was home to an ocean. But today, a dense atmosphere of carbon dioxide covers an almost waterless surface where temperatures exceed 450 ° C. The clouds in the sky are unattractive, they contain droplets of 90% sulfuric acid.
Conditions on Venus are so deeply unpleasant that many scientists believe the planet is dead. Rather than come from floating Venusians, they suspect that phosphine arises from more mundane processes.
“It’s completely surprising to say that life could survive surrounded by so much sulfuric acid,” said Professor Jane Greaves, an astronomer at Cardiff University, leader of the team that made the discovery. “But all the geological and photochemical routes that we can think of are too unproductive to produce the phosphine that we see.”
On Earth, phosphine gas is released by microbes in oxygen-deprived environments, such as the sediments of lakes and the entrails of animals. Other production routes are so extreme, the bellies of Jupiter and Saturn, that on rocky planets, phosphine is considered a marker of life.
As a test to search for life beyond Earth, Greaves observed Venus in 2017 with the James Clerk Maxwell telescope in Hawaii, and in 2019 with the Alma telescope in Chile. Both revealed the phosphine signature in the upper cloud layer of Venus.
Greaves first saw the phosphine signal one day in December 2018, when he was about to leave work. “There was no one to talk to and I remember thinking the best way to celebrate was to make a curry, so I went to Sainsbury’s,” he said.
The observations aim to track phosphine levels, around 20 molecules per billion, at least 30 miles up in the sky of Venus. Most appear in mid-latitudes and none are detected at the poles, the scientists report in Nature Astronomy.
While the phosphine may come from a mysterious new source, the researchers’ calculations rule out known chemistry and show that volcanoes, lightning strikes, and micrometeorites would create very little. “The production rates are so small, and the destruction rates great enough, that you would have a thousand times less,” said Paul Rimmer, an astrochemist on the team at the University of Cambridge.
To generate the amount of phosphine observed, terrestrial microbes would need to work at only 10% of their maximum productivity, the scientists say.
Sara Seager, a planetary scientist on the MIT study in the United States, called the finding “mind-blowing.” She hypothesizes a life cycle for Venusian microbes that rain, dry out, and are carried to warmer altitudes by currents in the atmosphere.
Charles Cockell, an astrobiologist at the University of Edinburgh, said that rather than hinting at life on Venus, the work raises questions about phosphine as a “biomarker.”
“A biological explanation should always be the explanation of last resort and there are good reasons to think that Venusian clouds are dead. The sulfuric acid concentrations in those clouds are more extreme than any known habitat on Earth, “he said.
Lewis Dartnell, an astrobiologist at the University of Westminster, said the findings would spur more work. “This is a great opportunity for ground-based telescope follow-up observations, and ideally to scrutinize these droplets in the atmosphere of Venus with a balloon probe drifting through acid clouds.”
