Phosphine on Venus Cannot be Explained by Conventional Processes

Abstract

The recent candidate detection of ~1 ppb of phosphine in the middle atmosphere of Venus is so unexpected that it requires an exhaustive search for explanations of its origin. Phosphorus-containing species have not been modelled for Venus' atmosphere before and our work represents the first attempt to model phosphorus species in the Venusian atmosphere. We thoroughly explore the potential pathways of formation of phosphine in a Venusian environment, including in the planet's atmosphere, cloud and haze layers, surface, and subsurface. We investigate gas reactions, geochemical reactions, photochemistry, and other non-equilibrium processes. None of these potential phosphine production pathways are sufficient to explain the presence of ppb phosphine levels on Venus. If PH3's presence in Venus' atmosphere is confirmed, it therefore is highly likely to be the result of a process not previously considered plausible for Venusian conditions. The process could be unknown geochemistry, photochemistry, or even aerial microbial life, given that on Earth phosphine is exclusively associated with anthropogenic and biological sources. The detection of phosphine adds to the complexity of chemical processes in the Venusian environment and motivates in situ follow up sampling missions to Venus. Our analysis provides a template for investigation of phosphine as a biosignature on other worlds.

v2 is in press in Astrobiology, Special Collection: Venus; v2 also expands on the potential of phosphides from the deep mantle volcanism as a source of PH3 (as suggested by Truong and Lunine 2021: https://www.pnas.org/content/118/29/e2021689118) and shows the volcanic source of PH3 to be unlikely

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Cited by in corpus (16)

• Production of Ammonia Makes Venusian Clouds Habitable and Explains Observed Cloud-Level Chemical Anomalies
• Was Venus Ever Habitable? Constraints from a Coupled Interior-Atmosphere-Redox Evolution Model
• Phosphine in the Venusian Atmosphere: A Strict Upper Limit from SOFIA GREAT Observations
• Data availability and requirements relevant for the Ariel space mission and other exoplanet atmosphere applications
• Low levels of sulphur dioxide contamination of Venusian phosphine spectra
• Large Interferometer For Exoplanets (LIFE): VIII. Where is the phosphine? Observing exoplanetary PH3 with a space based MIR nulling interferometer
• Mission Architecture to Characterize Habitability of Venus Cloud Layers via an Aerial Platform
• Astrobiological Potential of Venus Atmosphere Chemical Anomalies and Other Unexplained Cloud Properties
• Constraints on the production of phosphine by Venusian volcanoes
• Venusian phosphine: a 'Wow!' signal in chemistry?
• Proposed energy-metabolisms cannot explain the atmospheric chemistry of Venus
• Recovering Phosphine in Venus' Atmosphere from SOFIA Observations
• Large Uncertainties in the Thermodynamics of Phosphorus (III) Oxide (P${}_4$O${}_6$) Have Significant Implications for Phosphorus Species in Planetary Atmospheres
• A Large-scale Approach to Modelling Molecular Biosignatures: The Diatomics
• Powerful lightning on Venus constrained by atmospheric NO
• Necessary Conditions for Earthly Life Floating in the Venusian Atmosphere