Water has long been the gold standard for life, but new research from MIT suggests it may not be the only game in town. In laboratory experiments, scientists discovered that ionic liquids, salty fluids that stay liquid at high temperatures and low pressures, can form naturally from planetary materials.
The finding, published in the Proceedings of the National Academy of Sciences, suggests that even warm, rocky planets without water could have stable liquid environments capable of supporting life’s chemistry.
From Accident to Insight
The discovery began with research focused on Venus’s cloud chemistry. Rachana Agrawal, then a postdoctoral researcher at MIT, and planetary scientist Sara Seager were experimenting with ways to evaporate sulfuric acid from atmospheric samples to search for organic molecules. When sulfuric acid was mixed with glycine, a common amino acid, most of the acid evaporated as planned—but a persistent droplet remained. Further analysis revealed it was an ionic liquid, created by the acid transferring hydrogen atoms to the organic compound.
“We consider water to be required for life because that is what’s needed for Earth life. But if we look at a more general definition, we see that what we need is a liquid in which metabolism for life can take place.” — Rachana Agrawal.
Planetary Chemistry at Work
Ionic liquids are salts with melting points below 100°C. Unlike water, they have extremely low vapor pressures, so they do not evaporate easily and remain liquid under extreme conditions that would boil away or freeze water. The team mixed concentrated sulfuric acid with more than thirty nitrogen-containing organic compounds—including amino acids, nucleic acid bases, and other molecules relevant to life—and found that ionic liquids formed across a broad range of temperatures and pressures. The reaction was also successful on basalt rock surfaces, which are common on rocky planets, according to recent findings in astrobiology.
On a planetary scale, sulfuric acid can be produced by volcanic activity, while nitrogen-containing organics are widespread in the solar system and beyond. Where these ingredients meet on a waterless world, small pockets of ionic liquid could persist for years or even millennia, offering a potential habitat for life as described in Astrobiology.com.
Key Findings
- Ionic liquids formed at temperatures up to 180°C and at pressures far lower than those on Earth.
- These liquids remained stable on basalt rock even after excess sulfuric acid evaporated.
- Some biomolecules, including proteins and enzymes, can dissolve and remain stable within ionic liquids (arXiv).
- Sulfuric acid and nitrogen-bearing organics have plausible planetary origins, such as volcanic activity and delivery by asteroids.
Life Without Water
No ionic liquids are known to occur naturally on Earth, but they are common in industrial chemistry and surprisingly found in the mixing of venoms from rival ant species, as reported in ScienMag. The MIT team suggests that in extraterrestrial settings, ionic liquids could serve as alternative solvents for life. Laboratory studies have demonstrated that some biomolecules remain functional in pure ionic liquids, without water, introducing the possibility of non-water-based ecosystems according to NIH researchers.
“If we include ionic liquid as a possibility, this can dramatically increase the habitability zone for all rocky worlds,” Agrawal said.
Expanding the Habitable Zone
This work questions the traditional focus on planets located in the “Goldilocks zone” where liquid water exists. Instead, it points to a broader spectrum of habitable environments, including warm super-Earths with thin atmospheres and even atmosphereless bodies, assuming the liquids are shielded from intense radiation. Seager highlights the potential for future telescopes to detect ionic liquids indirectly—through chemical signatures or pigments from possible ionic-liquid-based life, as discussed in recent planetary habitability research.
What Comes Next
The MIT group will continue investigating which biomolecules can survive and operate in these unusual fluids. If confirmed, ionic-liquid worlds could join ocean-bearing moons and methane-lake planets as legitimate candidates in the ongoing search for extraterrestrial life.
Journal: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.2425520122)
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