Planets without water could still produce certain liquids, a new study finds

Water is essential for life on earth. Thus, liquid must be a requirement for life in other worlds. For decades, the definition of scientists of habitability on other planets is based on this hypothesis.

But what makes certain planets habitable could have very little to do with water. In fact, a completely different type of liquid could in theory support life in the worlds where water can barely exist. It is a possibility that MIT scientists raise in a study appearing this week in the Proceedings of the National Academy of Sciences.

According to laboratory experiments, researchers have discovered that a type of liquid known as ion liquid can be easily formed from chemical ingredients which should also be found on the surface of certain planets and rocky moons. Ionic liquids are salts that exist in liquid form less than around 100 degrees Celsius.

The experiences of the team have shown that a mixture of sulfuric acid and certain organic compounds containing nitrogen produced such a liquid. On the rocky planets, sulfuric acid can be a by-product of volcanic activity, while compounds containing nitrogen have been detected on several asteroids and planets of our solar system, which suggests that the compounds can be present in other planetary systems.

Ionic liquids have extremely low steam pressure and do not evaporate; They can form and persist at higher temperatures and lower pressures than liquid water can tolerate. Researchers note that ionic liquid can be a hospital environment for certain biomolecules, such as certain proteins that can remain stable in the liquid.

Scientists propose that even on too hot planets or who have too low pressure atmospheres to support liquid water, there could still be pockets of ion liquid. And where there is liquid, there can be a potential of life, but probably nothing that does not look like the water -based beings of the earth.

“We consider that water is necessary for life because it is what is necessary for the life of the earth. But if we look at a more general definition, we see that what we need is a liquid in which the metabolism for life can take place,” explains Rachana Agrawal, who led the study as a postdoc in the MIT department, atmospheric and planetary sciences. “Now, if we include ionic liquid as possibility, this can considerably increase the habitability area for all rocky worlds.”

The co-authors of the MIT of the study are Sara Seager, professor of planetary sciences of the 1941 class in the department of land, atmospheric and planetary sciences and professor in the departments of physics and aeronautics and astronautics, with Iaroslav Iakubivskyi, Weston Buchanan, Ana Glidcheng. The co-authors also include Maxwell Seager from Worcester Polytechnic Institute, William Bains from the University of Cardiff and Janusz Petkowski of the University of Wroclaw, in Poland.

A liquid jump

The work of the team with Ionic Liquid was born out of an effort to seek signs of life on Venus, where clouds of sulfuric acid envelop the planet in a harmful mist. Despite its toxicity, Venus clouds can contain signs of life – a notion that scientists predict to test with the missions to come in the atmosphere of the planet.

Agrawal and Seager, which leads the morning star missions to Venus, investigated the means of collecting and evaporating sulfuric acid. If a mission collects samples in the Venus clouds, sulfuric acid should be evaporated in order to reveal all the residual organic compounds which could then be analyzed for signs of life.

The researchers used their low -pressure personalized system designed to evaporate into excess sulfuric acid, to test the evaporation of an acid solution and an organic compound, of the glycine. They found that in all cases, while most of the liquid sulfuric acid evaporated, a stubborn layer of liquid has always remained.

They quickly realized that sulfuric acid reacted chemically with glycine, resulting in an exchange of hydrogen atoms from acid to organic compound. The result was a fluid mixture of salts, or ions, known as ionic liquid, which persists as a liquid through a wide range of temperatures and pressures.

This accidental discovery was launched an idea: could the ionic liquid form on too hot planets and host atmospheres that are too thin for water to exist?

“From there, we took the jump from the imagination of what it could mean,” said Agrawal. “Sulfuric acid is found on earth from volcanoes, and organic compounds were found on asteroids and other planetary bodies. So, this has led us to wonder if the ionic liquids could potentially form and exist on exoplanets.”

Rocky oasis

On earth, ionic liquids are mainly synthesized for industrial purposes. They do not occur naturally, except in a specific case, in which the liquid is generated from the mixture of venoms produced by two rival species of ants.

The team decided to study under what conditions the ionic liquid could be produced naturally, and on which range of temperatures and pressures. In the laboratory, they mixed sulfuric acid with various organic compounds containing nitrogen. In previous work, the Seager team had discovered that compounds, some of which can be considered as ingredients associated with life, are surprisingly stable in sulfuric acid.

“In high school, you learn that an acid wants to give a proton,” says Seager. “And curiously, we knew through our work passed with sulfuric acid (the main component of Venus clouds) and the compounds containing nitrogen, that a nitrogen wants to receive a hydrogen. It is as if the trash of one person was the treasure of another person.”

The reaction could produce a little ionic liquid if the sulfuric acid and the nitrogen body were in one report one – a report that was not an objective of previous work. For their new study, Seaager and Agrawal mixed sulfuric acid with more than 30 organic compounds containing different nitrogen, through a range of temperatures and pressures, then observed if the ionic liquid formed when they evaporated the sulfuric acid in various bottles. They also mixed the ingredients on basalt rocks, which are known to exist on the surface of many rocky planets.

“We were just surprised that the ionic liquid forms in many different conditions,” explains Seager. “If you put the sulfuric acid and the organic on a rock, the excess of sulfuric acid infiltrates the pores of the rock, but you always have with a drop of ion liquid on the rock. Everything we have tried, an ionic liquid is always formed.”

The team found that reactions produced ionic fluid at temperatures up to 180 degrees Celsius and to extremely low pressures – a little lower than that of the earth’s atmosphere. Their results suggest that ionic liquids could naturally form on other planets where liquid water cannot exist, under the right conditions.

“We are considering a planet warmer than the earth, which has no water, and at some point in its past or currently, it must have had sulfuric acid, formed from volcanic overtaking”, explains Seager. “This sulfuric acid must circulate on a small pocket of organic. And organic deposits are extremely common in the solar system.”

Then, she says, the resulting liquid pockets could remain on the surface of the planet, potentially for years or millennia, where they could theoretically serve small oasis for simple forms of life based on ionic liquid. In the future, the Seager team plans to investigate more, to see what biomolecules and life ingredients could survive and prosper in ionic fluid.

“We have just opened a box of new research from a pandora,” said Seager. “It was a real trip.”

This story is republished with the kind authorization of Mit News (Web.mit.edu/newsoffice/), a popular site that covers news of research, innovation and MIT teaching.