DISCOVERIES
An international team of astronomers have detected a mysterious molecule which may be the by-product of living cells
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Ateam of astronomers have detected the molecule phosphine in clouds above the surface of Earth’s neighbour, Venus. The team suggested that the phosphine could be produced by microbial life floating in the planet’s highly acidic clouds.
The researchers spotted the signature of phosphine using the James Clerk Maxwell Telescope (JCMT) in Hawaii, and studied it further with the Atacama Large Millimeter/ submillimeter Array (ALMA) in Chile. On Earth, the only sources of phosphine are industrial processes, and microbes that live in an oxygen-free environment. This led the team to consider whether the molecule might be a biosignature of alien life.
“This was an experiment made out of pure curiosity, really – taking advantage of JCMT’s powerful technology, and thinking about future instruments,” said Prof Jane Greaves of Cardiff University, who led the research team. “I thought we’d just be able to rule out extreme scenarios, like the clouds being stuffed full of organisms. When we got the first hints of phosphine in Venus’s spectrum, it was a shock!”
So, have the team found signs of alien life? “We have no idea if this is what is going on, but at the moment it seems less impossible than other explanations,” said team member Dr Anita Richards of the University of Manchester who coordinated the project with the ALMA telescopes in Chile.
They found the phosphine using a technique called absorption spectroscopy. Absorption spectroscopy analyses the light from a nearby star, in this case the Sun, that has passed through the atmosphere of a planet. Since every molecule will absorb a unique set of wavelengths of light, astronomers can use the star’s light to determine what substances are present in the atmosphere.
The amount of phosphine found in the atmosphere is tiny – only 20 molecules in a billion – but it is still far more than the team could explain away.
Dr William Bains, from the Massachusetts Institute of Technology, led the work on finding alternative explanations for the presence of phosphine. They studied sunlight, minerals blown upwards from the surface, volcanoes and lightning, but none of these could produce more than 0.0001 per cent of the phosphine that was found.
“At the moment, we can’t explain how enough phosphine molecules could survive long enough in the Venus cloud decks to allow us to detect it,” said Richards.
However, not all scientists are convinced. “I think that the simplest explanation is that we don’t understand the photochemistry and geochemistry of the Venusian atmosphere,” said Prof Charles Cockell, an astrobiologist at the University of Edinburgh who was not involved in the research. “I would always say that biology is a last resort when you’ve ruled out all other explanations.”
Part of the problem comes down to Venus’s inhospitable atmosphere. Even though the clouds provide a comfortable temperature and pressure, any life would have to deal with 90 per cent sulphuric acid. “There’s no environment on the Earth similar to that that can sustain life,” said Cockell. “So for me, the life explanation is not plausible.”
Even so, Cockell is excited. “I think, despite all my negativism, it is very exciting,” he said. “There might be planets that are habitable where [phosphine] is a signature of biology. So, being able to detect it in another planetary atmosphere is an immensely important thing to be able to do. It’s a really good contribution to the search for life in exoplanets.”
The next steps for the team are to spend more telescope time looking at the clouds of Venus, hunting for other biosignatures and studying exactly where the phosphine is found. Future space missions could also play a role in searching our planetary neighbour for signs of life.
“When we got the first hints of phosphine in Venus’s spectrum, it was a shock!”