Kavli Affiliate: Sara Seager
| First 5 Authors: William Bains, Janusz J. Petkowski, Sara Seager, ,
| Summary:
Life is a complex, dynamic chemical system that requires a dense fluid
solvent in which to take place. A common assumption is that the most likely
solvent for life is liquid water, and some researchers argue that water is the
only plausible solvent. However, a persistent theme in astrobiological research
postulates that other liquids might be cosmically common, and could be solvents
for the chemistry of life. In this paper we present a new framework for the
analysis of candidate solvents for life, and deploy this framework to review
substances that have been suggested as solvent candidates. We categorize each
solvent candidate through four criteria: occurrence, solvation, solute
stability and solvent chemical functionality. Our semi-quantitative approach
addresses all the requirements for a solvent not only from the point of view of
its chemical properties but also from the standpoint of their biochemical
function. Only the protonating solvents fulfil all the chemical requirements to
be a solvent for life, and of those only water and concentrated sulfuric acid
are also likely to be abundant in a rocky planetary context. Among the
non-protonating solvents liquid CO2 stands out as a planetary solvent, and its
potential as a solvent for life should be explored. We conclude with a
discussion of whether it is possible for a biochemistry to change solvents, as
an adaptation to radical changes in a planet’s environment. Our analysis
provides the basis for prioritizing future experimental work exploring
potential complex chemistry on other planets.
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