Phosphine Gas in the Cloud Decks of Venus

Measurements of trace gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our nearest neighbour, Venus, has cloud decks that are temperate but hyperacidic. Here we report the apparent presence of phosphine (PH 3) gas in Venus’s atmosphere, where any phosphorus should be in oxidized forms. Single-line millimetre-waveband spectral detections (quality up to ~15σ) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH 3 at ~20 ppb abundance is inferred. The presence of PH 3 is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently known abiotic production routes in Venus’s atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. PH 3 could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of PH 3 on Earth, from the presence of life. Other PH 3 spectral features should be sought, while in situ cloud and surface sampling could examine sources of this gas.