Phosphine gas (PH3) has been detected in the clouds of Venus (Greaves, J.S., Richards, A.M.S., Bains, W. et al., Nat Astron (2020). The absorption line at 267 GHz was first seen in JCMT spectra, and followed up with ALMA in 2019. The line-shape indicates that it arises at 50-60 km above the surface, where the temperature and pressure are within ‘terrestrial’ ranges but the atmosphere is vastly more acid than Earth’s. After exhaustive modelling, the presence of even a few parts per billion of PH3 could not be explained by steady-state chemistry, photochemical pathway, volcanism, meteoric delivery or the effects of lightning. Some routes might form tiny traces of PH3 but it would react rapidly with the violently oxidising atmosphere of Venus. Thus, some mechanism must be replenishing the PH3 supply and the detection of a non-equilibrium mixture of gases has long been considered a possible marker of life, especially as it is known to be produced biologically on Earth. We look forward to the possibility of follow-up observations with ALMA and eventually to space missions to investigate further this tantalising result.
RadioNet (MARCUs) supported Prof. Jane Greaves (Cardiff University) in visiting the UK ALMA Regional Centre to analyse the data.
Text © Anita Richards (Uni. Manchester) – leader of the RadioNet Training Activity
Images © Main picture – Joanna Pętkowska, PhD, Background – Akatsuki (Japan) orbiter, The spectra – ALMA and JCMT