Phosphine Gas in the Cloud Decks of Venus

TL;DR

Detection of phosphine gas in Venus's atmosphere suggests potential unknown chemical processes or possible biological activity, challenging current understanding of Venusian chemistry.

Contribution

First report of phosphine detection in Venus's clouds using millimeter-wave spectroscopy, highlighting unexplained presence with no known abiotic sources.

Findings

Phosphine detected at ~20 ppb in Venusian atmosphere.

No known abiotic processes account for phosphine presence.

Potential implications for Venusian geochemistry or life.

Abstract

Measurements of trace-gases in planetary atmospheres help us explore chemical conditions different to those on Earth. Our nearest neighbor, Venus, has cloud decks that are temperate but hyper-acidic. We report the apparent presence of phosphine (PH3) gas in Venusian atmosphere, where any phosphorus should be in oxidized forms. Single-line millimeter-waveband spectral detections (quality up to ~15 sigma) from the JCMT and ALMA telescopes have no other plausible identification. Atmospheric PH3 at ~20 parts-per-billion abundance is inferred. The presence of phosphine is unexplained after exhaustive study of steady-state chemistry and photochemical pathways, with no currently-known abiotic production routes in Venusian atmosphere, clouds, surface and subsurface, or from lightning, volcanic or meteoritic delivery. Phosphine could originate from unknown photochemistry or geochemistry, or, by analogy with biological production of phosphine on Earth, from the presence of life. Other PH3 spectral features should be sought, while in-situ cloud and surface sampling could examine sources of this gas.