Kavli Affiliate: Sara Seager
| First 5 Authors: , , , ,
| Summary:
The discovery of thousands of exoplanets and the emergence of telescopes
capable of exoplanet atmospheric characterization have intensified the search
for habitable worlds. Due to selection biases, many exoplanets under study are
planets deemed inhospitable because their surfaces are too warm to support
liquid water. We propose that such planets could still support life through
ionic liquids: Liquid salts with negligible vapor pressure that can persist on
warm planets with thin atmospheres, where liquid water cannot. Ionic liquids
have not previously been considered as naturally occurring substances, and thus
have not been discussed in planetary science. We demonstrate in laboratory
experiments that ionic liquids can form from planetary materials: Sulfuric acid
combined with nitrogen-containing organic molecules. Sulfuric acid can be
volcanic in origin, and organic compounds are commonly found on planetary
bodies. The required planetary surface is water-depleted and must support
sulfuric acid transiently in liquid phase to dissolve organics, followed by
evaporation of excess liquid, conditions spanning approximately 300 K at 10^-7
atm to 350-470 K at 0.01 atm. Because ionic liquids have extremely low vapor
pressures, they are not prone to evaporation, allowing small droplets or pools
to persist without ocean-like reservoirs. Ionic liquids’ minuscule vapor
pressure at room temperature suggests possible stability on planets with
negligible atmospheres, shielded by magnetic fields or rock crevices against
harsh cosmic radiation. Ionic liquids can stably dissolve enzymes and other
biomolecules, enabling biocatalysis and offering a plausible solvent for life,
broadening the definition of habitable worlds.
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