Planets with out water may nonetheless produce sure liquids, a brand new examine finds | MIT Information

Water is crucial for all times on Earth. So, the liquid should be a requirement for all times on different worlds. For many years, scientists’ definition of habitability on different planets has rested on this assumption.

But what makes some planets liveable may need little or no to do with water. In truth, a wholly completely different kind of liquid may conceivably help life in worlds the place water can barely exist. That’s a risk that MIT scientists increase in a examine appearing this week within the Proceedings of the National Academy of Sciences.

From lab experiments, the researchers discovered {that a} kind of fluid often called an ionic liquid can readily type from chemical components which can be additionally anticipated to be discovered on the floor of some rocky planets and moons. Ionic liquids are salts that exist in liquid type under about 100 levels Celsius. The crew’s experiments confirmed {that a} combination of sulfuric acid and sure nitrogen-containing natural compounds produced such a liquid. On rocky planets, sulfuric acid could also be a byproduct of volcanic exercise, whereas nitrogen-containing compounds have been detected on a number of asteroids and planets in our photo voltaic system, suggesting the compounds could also be current in different planetary methods.

Ionic liquids have extraordinarily low vapor stress and don’t evaporate; they’ll type and persist at greater temperatures and decrease pressures than what liquid water can tolerate. The researchers observe that ionic liquid generally is a hospitable setting for some biomolecules, equivalent to sure proteins that may stay secure within the fluid.

The scientists suggest that, even on planets which can be too heat or which have atmospheres are too low-pressure to help liquid water, there may nonetheless be pockets of ionic liquid. And the place there may be liquid, there could also be potential for all times, although seemingly not something that resembles Earth’s water-based beings.

“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,” says Rachana Agrawal, who led the examine as a postdoc in 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 examine’s MIT co-authors are Sara Seager, the Class of 1941 Professor of Planetary Sciences within the Department of Earth, Atmospheric and Planetary Sciences and a professor within the departments of Physics and of Aeronautics and Astronautics, together with Iaroslav Iakubivskyi, Weston Buchanan, Ana Glidden, and Jingcheng Huang. Co-authors additionally embody Maxwell Seager of Worcester Polytechnic Institute, William Bains of Cardiff University, and Janusz Petkowski of Wroclaw University of Science and Technology, in Poland.

A liquid leap

The crew’s work with ionic liquid grew out of an effort to seek for indicators of life on Venus, the place clouds of sulfuric acid envelope the planet in a noxious haze. Despite its toxicity, Venus’ clouds could comprise indicators of life — a notion that scientists plan to check with upcoming missions to the planet’s environment.

Agrawal and Seager, who’s main the Morning Star Missions to Venus, had been investigating methods to gather and evaporate sulfuric acid. If a mission collects samples from Venus’ clouds, sulfuric acid must be evaporated away in an effort to reveal any residual natural compounds that would then be analyzed for indicators of life.

The researchers had been utilizing their customized, low-pressure system designed to evaporate away extra sulfuric acid, to check evaporation of an answer of the acid and an natural compound, glycine. They discovered that in each case, whereas a lot of the liquid sulfuric acid evaporated, a cussed layer of liquid at all times remained. They quickly realized that sulfuric acid was chemically reacting with glycine, leading to an alternate of hydrogen atoms from the acid to the natural compound. The end result was a fluid combination of salts, or ions, often called an ionic liquid, that persists as a liquid throughout a variety of temperatures and pressures.

This unintended discovering kickstarted an concept: Could ionic liquid type on planets which can be too heat and host atmospheres too skinny for water to exist?

“From there, we took the leap of imagination of what this could mean,” Agrawal says. “Sulfuric acid is found on Earth from volcanoes, and organic compounds have been found on asteroids and other planetary bodies. So, this led us to wonder if ionic liquids could potentially form and exist naturally on exoplanets.”

Rocky oases

On Earth, ionic liquids are primarily synthesized for industrial functions. They don’t happen naturally, apart from in a single particular case, wherein the liquid is generated from the blending of venoms produced by two rival species of ants.

The crew got down to examine what situations ionic liquid could possibly be naturally produced in, and over what vary of temperatures and pressures. In the lab, they combined sulfuric acid with varied nitrogen-containing natural compounds. In earlier work, Seager’s crew had discovered that the compounds, a few of which might be thought-about components related to life, are surprisingly secure in sulfuric acid.

“In high school, you learn that an acid wants to donate a proton,” Seager says. “And oddly enough, we knew from our past work with sulfuric acid (the main component of Venus’ clouds) and nitrogen-containing compounds, that a nitrogen wants to receive a hydrogen. It’s like one person’s trash is another person’s treasure.”

The response may produce a little bit of ionic liquid if the sulfuric acid and nitrogen-containing organics had been in a one-to-one ratio — a ratio that was not a spotlight of the prior work. For their new examine, Seager and Agrawal combined sulfuric acid with over 30 completely different nitrogen-containing natural compounds, throughout a variety of temperatures and pressures, then noticed whether or not ionic liquid shaped once they evaporated away the sulfuric acid in varied vials. They additionally combined the components onto basalt rocks, that are recognized to exist on the floor of many rocky planets.

“We were just astonished that the ionic liquid forms under so many different conditions,” Seager says. “If you put the sulfuric acid and the organic on a rock, the excess sulfuric acid seeps into the rock pores, but you’re still left with a drop of ionic liquid on the rock. Whatever we tried, ionic liquid still formed.”

The crew discovered that the reactions produced ionic liquid at temperatures as much as 180 levels Celsius and at extraordinarily low pressures — a lot decrease than that of the Earth’s environment. Their outcomes recommend that ionic liquid may naturally type on different planets the place liquid water can not exist, underneath the proper situations.

“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 says. “This sulfuric acid has to flow over a little pocket of organics. And organic deposits are extremely common in the solar system.”

Then, she says, the ensuing pockets of liquid may keep on the planet’s floor, doubtlessly for years or millenia, the place they may theoretically function small oases for easy types of ionic-liquid-based life. Going ahead, Seager’s crew plans to research additional, to see what biomolecules, and components for all times, would possibly survive, and thrive, in ionic liquid.

“We just opened up a Pandora’s box of new research,” Seager says. “It’s been a real journey.”

This analysis was supported, partly, by the Sloan Foundation and the Volkswagen Foundation.