life Article Evaluating Alternatives to Water as Solvents for Life: The Example of Sulfuric Acid William Bains 1,2,*, Janusz Jurand Petkowski 1 , Zhuchang Zhan 1 and Sara Seager 1,3,4 1 Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;
[email protected] (J.J.P.);
[email protected] (Z.Z.);
[email protected] (S.S.) 2 School of Physics & Astronomy, Cardiff University, 4 The Parade, Cardiff CF24 3AA, UK 3 Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 4 Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA * Correspondence:
[email protected] Abstract: The chemistry of life requires a solvent, which for life on Earth is water. Several alternative solvents have been suggested, but there is little quantitative analysis of their suitability as solvents for life. To support a novel (non-terrestrial) biochemistry, a solvent must be able to form a stable solution of a diverse set of small molecules and polymers, but must not dissolve all molecules. Here, we analyze the potential of concentrated sulfuric acid (CSA) as a solvent for biochemistry. As CSA is a highly effective solvent but a reactive substance, we focused our analysis on the stability of chemicals in sulfuric acid, using a model built from a database of kinetics of reaction of molecules with CSA. We consider the sulfuric acid clouds of Venus as a test case for this approach. The large majority of terrestrial biochemicals have half-lives of less than a second at any altitude in Venus’s clouds, but three sets of human-synthesized chemicals are more stable, with average half-lives of days to weeks at the conditions around 60 km altitude on Venus.