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Biosignature in clouds of Venus ‘very hard to explain without life’

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An international team of scientists have announced the discovery of phosphine in the atmosphere of Venus. They caution while this cannot be explained through any known chemical processes, it would also be difficult to explain how life could survive in Venus’ inhospitable atmosphere.

The presence of phosphine – a molecule consisting of one phosphorous atom and three hydrogen atoms – is considered a 'biomarker', since it would be difficult to explain its presence without the presence of life. It is found in Earth’s atmosphere, and most commonly produced through the decomposition of organic matter.

Now, a collaboration of scientists from Cardiff University, the University of Manchester, MIT, and other institutions have confirmed the presence of small amounts of phosphine (around twenty molecules in every billion) in the upper atmosphere of Venus.

They made their detections and confirmations through observations at a wavelength of 1mm, using the James Clerk Maxwell telescope in Hawaii and then the Atamaca Large Millimeter Array in Chile.

Speaking in a short, pre-recorded message streamed by the Royal Astronomical Society, lead author of the Nature Astronomy study Professor Jane Greaves explained that phosphine is considered a biomarker on Earth; it can be traced back to a biological origin. After the scientists discovered and confirmed the presence of phosphine in the atmosphere, they looked at how it may have emerged from natural processes, such as through minerals emerging from the ground of the planet.

However, they ruled out all these possibilities, with their paper stating that its presence is “unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’ atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery.” Natural sources were found to make at most one ten thousandth of the amount of phosphine that the telescopes saw.

“On Earth, phosphine can be made in two ways; it is made industrially for some purpose […] it’s also made by microbes, small bacteria for example, and they’re the kind of bacteria that thrive when there’s no oxygen, so they’re used to a very different way of life than we are,” said Greaves.

She explained that there has been speculation that there could be habitable parts of the cloud decks of Venus at an altitude of around 50km: ten times higher than we consider the top of Earth’s atmosphere. At these heights the atmosphere is extremely acidic, but warm at around 20°C and with pressure of 1bar (similar to the surface of Earth).

Greaves said in the pre-recorded message that it is “very hard to explain the presence of a molecule like phosphine without life” – as it would have to originate from entirely unknown chemical processes – but also very difficult to explain how life would thrive in the hyperacidic (around 90 per cent sulphuric acid) environment of the clouds of Venus.

Questioned on whether there is life on Venus, Greaves commented: “I really hope so, but we can’t absolutely tell with the results we’ve got so far, so it may be that the only thing we can do is send a spacecraft which can sample and show us if there are life forms there.”

The scientists are now awaiting more observation time to establish whether phosphine can be located in the temperate parts of the cloud deck and to search for other gases that may be associated with life.

Professor Emma Bunce, President of the Royal Astronomical Society, congratulated the team: “A key question in science is whether life exists beyond Earth, and 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.”

The Science Minister Amanda Solloway added: “Venus has for decades captured the imagination of scientists and astronomers around the world. This discovery is immensely exciting, helping us increase our understanding of the universe and even whether there could be life on Venus. I am incredibly proud that this fascinating detection was led by some of the UK’s leading scientists and engineers using state of the art facilities built on our own soil.”

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