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'Signs of life' on Venus might just be ordinary sulfur gas

The detection of phosphine theorized to be from microbes may have been caused instead by sulfur dioxide, which is not a clear sign of life.

The widely-publicized detection of phosphine gas on Venus – a possible "biosignature" suggesting the hellish planet could have living microbes in its clouds – was probably caused by an entirely different gas which is not a clear sign of life, according to new research.

Studies by a team of American scientists suggest the radio telescope observations thought to reveal phosphine on Venus were instead caused by sulfur dioxide, which gives signals that can be confused for phosphine under certain circumstances.

The latest research published in January also suggests the radio signals originated far above the Venusian clouds, where phosphine would quickly be destroyed by other chemicals – giving further weight to the idea that they were caused by sulfur dioxide.

The Magellan probe that orbited Venus from 1990 to 1994 was able to peer through the thick Venusian clouds and build up the above image by emitting and re-detecting cloud-penetrating radar.SSV, MIPL, Magellan Team, NASA

“Our new research makes the detection of phosphine a lot less likely,” said Victoria Meadows, an astrobiologist and professor of astronomy at the University of Washington in Seattle who helped lead the studies. “We can explain the observations straightforwardly using sulfur dioxide … and it doesn't require any unknown chemistry.”

Sulfur dioxide is a relatively common gas on Venus, where it’s thought to be caused by the chemistry of the thick, unbreathable atmosphere, and possibly by volcanoes. It’s also found in Earth’s atmosphere, where it comes mainly from volcanoes and from burning fossil fuels.

Phosphine gas, on the other hand, is created on Earth by some microorganisms as they digest organic matter, and so it’s considered a possible “biosignature” – which means its detection in the atmospheres of distant planets could be a sign of elementary life.

The British-led team of scientists which first reported the possible detection of phosphine on Venus said it knew of no chemical process that could produce it – leading to the suggestion that it could be from microbes floating in the planet’s clouds, miles above the superhot surface.

After the scientists reconsidered their initial findings with recalibrated data from the ALMA telescope in Chile’s Atacama Desert, they said they still thought they had detected phosphine on Venus, but much less of it. They now hope to give a detailed response to the new research in a few weeks.

Ignas Snellen, a professor of observational astrophysics at the University of Leiden in the Netherlands who was not involved in the latest studies, said it now seemed unlikely that there was any phosphine on Venus.

The recalibrated data from the ALMA telescopes showed no evidence of phosphine, and earlier detections by the James Clerk Maxwell radio telescope in Hawaii could now be explained as sulfur dioxide, he said.

“I think the story of phosphine and possible life on Venus stops here,” he said.