For some decades, space exploration missions have looked for evidence of life beyond Earth where we know that large bodies of water, such as lakes or oceans, exist or have previously existed. However, the new research shows that it isn’t the quantity of water that matters for making life viable, but the effective concentration of water molecules - known as ‘water activity’.
The new study also found that research published by an independent team of scientists last year, claiming that the phosphine gas in Venus’ atmosphere indicates possible life in the sulphuric acid clouds of Venus, is not plausible.
Through this innovative research project, Dr John E. Hallsworth from the School of Biological Sciences at Queen’s and his team of international collaborators devised a method to determine the water activity of atmospheres of a planet. Using their approach to study the sulphuric acid clouds of Venus, the researchers found that the water activity was more than a hundred times below the lower limit at which life can exist on Earth.
Dr Hallsworth comments: “Our research shows that the sulphuric acid clouds in Venus have too little water for active life to exist, based on what we know of life on Earth. We have also found that the conditions of water and temperature within Jupiter’s clouds could allow microbial-type life to subsist, assuming that other requirements such as nutrients are present.”
Co-author of the report, an expert on physics and chemical biology of water, Dr Philip Ball, says: “The search for extraterrestrial life has sometimes been a bit simplistic in its attitude to water. As our work shows, it’s not enough to say that liquid water equates with habitability. We’ve got to think too about how Earth-like organisms actually use it – which shows us that we then have to ask how much of the water is actually available for those biological uses.”
A plant scientist in extraterrestrial spheres
Dr Jürgen Burkhardt of the Institute of Crop Science and Resource Conservation (INRES), a member of the Phenorob Cluster of Excellence and the Transdisciplinary Research Area "Innovation and Technology for Sustainable Futures" at the University of Bonn, contributed to this study primarily by making calculations of water activity and sulphuric acid concentration in the cloud droplets of the Venusian atmosphere. The fact that a scientist researching plant nutrition is contributing to Life in the Venus Atmosphere is due to Dr Burkhardt's earlier work. He had previously used the aerosol model used in the study to characterize the state of deposited hygroscopic aerosols on leaf surfaces.
"These aerosols allow microorganisms to survive under certain conditions," Burkhardt says. A shared interest in this habitat and its very specific physicochemical conditions, such as high acid concentrations and minimal amounts of water, led to contact years ago with the study's first author, John Hallsworth. Experimental electron microscopy studies by Hallsworth and Burkhardt on this topic had already resulted in two earlier joint publications that also addressed the question of extraterrestrial life.
Participating institutions and funding:
Co-authors of this paper include planetary scientist Christopher P. McKay (NASA Ames Research Center, CA, USA); atmosphere chemistry expert Thomas Koop (Bielefeld University, Germany); expert on physics and chemical biology of water Philip Ball (London, UK); biomolecular scientist Tiffany D. Dallas (Queen’s University Belfast); biophysics-of-lipid-membrane expert Marcus K. Dymond (University of Brighton, UK); theoretical physicist María-Paz Zorzano (Centro de Astrobiologia [CSIC-INTA], Spain); micrometeorology and aerosol expert Juergen Burkhardt (University of Bonn, Germany); expert on acid-tolerant microorganisms Olga V. Golyshina (Bangor University, UK); and atmospheric physicist and planetary scientist Javier Martín-Torres (University of Aberdeen, UK).
The research was funded by Research Councils UK (RCUK) | Biotechnology and Biological Sciences Research Council (BBSRC) and Ministry of Science and Innovation.
Publication: John E. Hallsworth et al.: Water activity in Venus’s uninhabitable clouds and other planetary atmospheres, Nature Astronomy, DOI: 10.1038/s41550-021-01391-3
