THURSDAY, 17 SEPTEMBER 2020
With apocalyptic red clouds of carbon dioxide and sulfuric acid, temperatures hot enough to melt lead, and atmospheric pressures high enough to crumple a car, the surface of Venus hardly seems a welcoming environment for any form of extraterrestrial life. An international group of scientists including researchers at the University of Cambridge, however, has recently detected the presence of a chemical in the Venusian atmosphere that suggests life might have found a way to persist on the planet.The discovery, published in Nature Astronomy, took the team by surprise. They had intended to use their access to the powerful James Clerk Maxwell Telescope (JCMT) in Hawaii and the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile to test the capabilities of the technologies by scanning the atmosphere of Earth’s closest planetary neighbour. The telescopes examine light passing through the atmospheres of planets, returning ‘absorption spectra’ for scientists to interpret. Disruptions, or ‘gaps’, at particular positions along these spectra can point to the presence of molecules and atoms that absorb light at those particular wavelengths, preventing that light from returning to the telescope back on Earth. Somewhat unexpectedly, the team discovered a very faint absorption at a wavelength corresponding to the chemical phosphine, suggesting for the first time its presence in the atmosphere of Venus.
What makes this discovery so exciting is that phosphine, a colourless gas with an unpleasant ‘garlicky’ odour, is thought to be produced largely by living microbes, hinting at the possibility of life on the hostile planet.
The idea of life on Venus is not a new one, first popularised in the 1960s, and then solidified when scientists noticed that the cloud layer surrounding the planet sat at temperatures much cooler than the greenhouse gas-rich air at the surface and could be more inviting for microbial life. The search for ‘extremophiles’, or microbes that thrive in conditions considered uninhabitable by most Earth-bound life, comprises much of the modern-day search for life on other planets. What scientists often look for is evidence of chemical signatures suggesting either the presence of by-products formed by known biotic processes or the ‘building blocks’ required to kick-start them. The discovery of phosphine in the atmosphere, a compound normally expelled by microbes living in Earth’s oxygen-free pockets, suggests a similar process may be happening on Venus.
But the presence of the molecule doesn’t confirm the presence of life on the planet, the team warns. Phosphine can also be released on Earth as a result of a number of man-made or non-living processes, and we cannot rule out the possibility of similar chemical dynamics we are as yet unaware of happening on the planet that could explain the findings. The amounts of the chemical the study detected are encouraging, however. Phosphine was predicted to be present in only twenty molecules out of every one billion, making it scarce, but nearly one thousand times higher than is usually emitted by non-biotic processes, and unlikely to be the result of contamination from previous probes sent from Earth.
Dr Paul Rimmer, an atmospheric chemist at the Department of Earth Sciences in Cambridge, calculated that the quantities found would be very easy for Earth-dwelling microbes to produce, functioning at about 10% of their maximum productivity. It is important to remember though, he and the team warn, that the vast differences in atmospheric conditions make these comparisons preliminary in nature, as the microbes that could survive on Venus would likely be very different from their counterparts on Earth.
While the finding does not prove the presence of life outside our own green planet, it certainly provides an exciting new step forward in the search. The team now hopes to continue sampling the atmosphere of Venus to understand if the phosphine is detected in the more temperate and hospitable portions of the planet’s atmosphere. Next steps may even involve missions to visit Venus and sample these portions for further signs of life on the alien planet.
Juli Cudini is a PhD student at the Wellcome Sanger Institute studying microbiology and is a Finance Officer for BlueSci
References:
- Greaves, J.S., Richards, A.M.S., Bains, W. et al. Phosphine gas in the cloud decks of Venus. Nat Astron (2020)
- Sanjay S.L., Rakesh M., David J.S. et al. Venus' Spectral Signatures and the Potential for Life in the Clouds. Astrobiology (2018)
