For centuries, the search for life beyond Earth has been soaked in one belief: water is essential. Now, MIT researchers are challenging this planetary doctrine—suggesting that the ingredients for life could thrive in liquids far different from water, and perhaps on worlds much harsher than our own.
In a study published this week in Proceedings of the National Academy of Sciences, the MIT-led team demonstrated that a special blend of chemicals—known as ionic liquids—can easily form on rocky planets and moons, potentially creating new havens for life in the cosmos.
Ionic liquids are a type of salt that stays liquid at temperatures below 100°C and, unlike water, can endure extremes of heat and pressure. In their experiments, the researchers mixed sulfuric acid (often produced by volcanoes) with simple nitrogen-rich organic compounds (found on asteroids and planetary atmospheres). The result: a persistent, stable liquid that doesn’t evaporate even when most of the acid is gone.
Ionic liquids, it turns out, can be friendly to rare biomolecules—like hardy proteins—that can resist breakdown in harsh conditions.
Expanding the habitability zone
“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,” said Dr. Rachana Agrawal, who led the study at MIT’s Department of Earth, Atmospheric and Planetary Sciences. “Now if we include ionic liquid as a possibility, this can dramatically increase the habitability zone for all rocky worlds.”
The implications are staggering: even on planets that are too hot, or whose atmospheres are too thin for water to exist, stable ionic liquids could form and persist—potentially nurturing forms of alien life, though they may look nothing like Earth’s water-based organisms.
From Venus to beyond
The inspiration came when the team was working to solve a Venus mystery. Venus, shrouded in clouds of sulfuric acid, has long fascinated scientists seeking signs of life. When Dr. Agrawal and her colleagues tried to evaporate sulfuric acid from a solution to isolate organic molecules, a stubborn liquid layer wouldn’t go away. They realized they’d accidentally created an ionic liquid—a discovery that opened new doors in astrobiology.
Dr. Sara Seager, MIT’s Class of 1941 Professor of Planetary Sciences and co-leader of the study, described the breakthrough: “In high school, you learn that an acid wants to donate a proton. Oddly enough, we knew from our past work that sulfuric acid (the main component of Venus’ clouds) and nitrogen-containing compounds have this unique chemistry—one gives up a hydrogen, one takes it. It’s like one person’s trash is another person’s treasure.”
After testing over 30 nitrogen compounds with sulfuric acid, the scientists confirmed that ionic liquids reliably form under a wide range of conditions—even on basalt rocks similar to those on planetary surfaces.
“We were just astonished that the ionic liquid forms under so many different conditions,” Seager said. “If you put the sulfuric acid and the organic on a rock, the excess acid seeps into the pores, but you’re still left with a drop of ionic liquid. Whatever we tried, ionic liquid still formed.”
Their experiments showed that this process happens up to 180°C and at pressures far below Earth’s, broadening the realm of possible habitable worlds.
New oases in the universe
Imagine a rocky world, hotter than Earth, where volcanic sulfuric acid flows over pockets of organic matter—ingredients for life scattered across the solar system. According to Dr. Seager, these spots could become long-lived pools of ionic liquid, tiny oases for simple, exotic life forms.
“We’re envisioning a planet warmer than Earth, that doesn’t have water, and at some point in its past or currently, it has to have had sulfuric acid, formed from volcanic outgassing,” Seager explained. “This sulfuric acid has to flow over a little pocket of organics. And organic deposits are extremely common in the solar system.”
Just how far could this discovery go? The team says much more work lies ahead. They will now focus on what kinds of molecules—and what forms of life—could actually flourish in these unearthly environments.
“We just opened up a Pandora’s box of new research,” Seager said. “It’s been a real journey.”
Contributors to the study include: MIT scientists Sara Seager, Rachana Agrawal, Iaroslav Iakubivskyi, Weston Buchanan, Ana Glidden, Jingcheng Huang; Maxwell Seager (Worcester Polytechnic Institute); William Bains (Cardiff University); Janusz Petkowski (Wroclaw University of Science and Technology).