By Abbas Nazil
MIT researchers have found that certain planets lacking water could still produce and sustain other types of liquids that might support life, challenging the long-standing assumption that water is a universal prerequisite for habitability.
The study, published in the Proceedings of the National Academy of Sciences, shows that a type of fluid called an ionic liquid can naturally form from chemical ingredients expected to be present on the surfaces of some rocky planets and moons.
Ionic liquids are salts that remain in liquid form below about 100 degrees Celsius and are stable at temperatures and pressures beyond the limits of liquid water.
Through lab experiments, the scientists discovered that mixing sulfuric acid with certain nitrogen-containing organic compounds produced an ionic liquid.
On rocky planets, sulfuric acid could originate from volcanic activity, while nitrogen-based organics have been detected on asteroids and other planetary bodies, indicating that the components for such reactions may be common in the universe.
Lead researcher Rachana Agrawal explained that water is considered essential for life because it supports metabolism on Earth, but if the definition of habitability is broadened to include any liquid that can enable metabolic processes, then ionic liquids significantly expand the potential habitable zones of rocky worlds.
The team’s findings stemmed from work related to Venus, a planet shrouded in sulfuric acid clouds.
While testing methods to evaporate sulfuric acid in a low-pressure system for possible Venus missions, Agrawal and MIT professor Sara Seager observed that when sulfuric acid was combined with glycine, part of the acid chemically reacted instead of fully evaporating, leaving behind an ionic liquid.
This unexpected result led them to hypothesize that such liquids could form naturally on planets too warm or with too little atmospheric pressure for water.
Subsequent experiments involved mixing sulfuric acid with over 30 nitrogen-containing organics under various temperatures and pressures, and even on basalt rock surfaces similar to those on many rocky planets.
In nearly every case, the acid and organics produced ionic liquids, persisting even when excess acid seeped into rock pores.
The reactions occurred at temperatures up to 180 degrees Celsius and at extremely low pressures, suggesting these liquids could remain stable for years or even millennia on planets that cannot host water.
Seager noted that a scenario where volcanic sulfuric acid flows over organic-rich areas could create small, stable pockets of liquid on such planets, potentially serving as microhabitats for non-water-based life forms.
The team now plans to study which biomolecules might survive and function in ionic liquids, opening what Seager described as a “Pandora’s box” of new research possibilities.