Venus' Atmospheric Chemistry and Cloud Characteristics Are Compatible with Venusian Life

Abstract

Venus is Earth's sister planet, with similar mass and density but an uninhabitably hot surface, an atmosphere with a water activity 50-100 times lower than anywhere on Earths' surface, and clouds believed to be made of concentrated sulfuric acid. These features have been taken to imply that the chances of finding life on Venus are vanishingly small, with several authors describing Venus' clouds as ''uninhabitable,'' and that apparent signs of life there must therefore be abiotic, or artefactual. In this article, we argue that although many features of Venus can rule out the possibility that Earth life could live there, none rule out the possibility of all life based on what we know of the physical principle of life on Earth. Specifically, there is abundant energy, the energy requirements for retaining water and capturing hydrogen atoms to build biomass are not excessive, defenses against sulfuric acid are conceivable and have terrestrial precedent, and the speculative possibility that life uses concentrated sulfuric acid as a solvent instead of water remains. Metals are likely to be available in limited supply, and the radiation environment is benign. The clouds can support a biomass that could readily be detectable by future astrobiology-focused space missions from its impact on the atmosphere. Although we consider the prospects for finding life on Venus to be speculative, they are not absent. The scientific reward from finding life in such an un-Earthlike environment justifies considering how observations and missions should be designed to be capable of detecting life if it is there.

Source of phosphine on Venus—An unsolved problem

“…Bains et al (2021b,c) showed that biochemical production of phosphine was not thermodynamically impossible, based on a model where an organism maintained a neutral aqueous interior while living in a sulfuric acid droplet, but did not speculate where the energy to do this might come from. Jordan et al (2022) show that some limited sulfur-based metabolic strategies either cannot provide enough energy, or would produce chemical signatures that contradict what is currently observed in Venus's atmosphere, but Bains et al (2024) show that more than enough solar energy is available for a biosphere in the clouds, and alternative photosynthetic metabolisms may not create the same anomalies in Venus's atmosphere as the metabolisms explored by Jordan et al Such an organism is therefore not ruled out by what we know of life, but nevertheless seems intuitively implausible.…”

“…The suggestion that the same logic could be applied to Venus has generated much heated argument, with several authors stating that Venus is uninhabitable because of the extreme aridity and acidity of its atmosphere, and hence that life could be ruled out a priori as a candidate source for phosphine (Cockell et al, 2021;Hallsworth et al, 2021). However, the potential habitability of the clouds is still debated (Bains et al, 2021a;Limaye et al, 2021a;Limaye et al, 2021b;Cleland and Rimmer, 2022;Bains et al, 2024), so we must take the habitability of Venus' cloud decks as unresolved.…”

Year-Long Stability of Nucleic Acid Bases in Concentrated Sulfuric Acid: Implications for the Persistence of Organic Chemistry in Venus’ Clouds

“…Venus has a surface that is too hot for any plausible solvent and the most complex organic chemistry; hence, it is unsuitable for supporting life. Nevertheless, scientists have speculated that the perpetual cloud cover at 48 to 60 km above Venus' surface, and with temperatures matching those found at Earth's surface, might host life (see, e.g., [1][2][3][4][5][6][7][8][9]). Venus clouds, however, are composed of concentrated sulfuric acid-an aggressive solvent that destroys most of Earth life's biochemicals and is thought to be sterile to complex organic chemistry or life of any kind.…”