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Alien worlds may not necessarily need water for life, scientists find: ‘We just opened a Pandora's box'
Water may not be essential to support life, and an entirely different type of liquid could do the same in alien worlds, a new study claims.
Until now, water has been considered a requirement for life on other worlds, with scientists defining the habitability of other planets based on its presence.
However, a new lab experiment suggests salts existing in liquid form at lower temperatures in other worlds may host life, though unlike anything resembling Earth's water-based beings.
Such liquid-salts, called ionic liquids, can exist below about 100 degrees Celsius and remain stable enough in the fluid state at wider conditions to be a hospitable environment for life-signature molecules like proteins, say researchers from the Massachussets Institute of Technology.
The study, published in the journal PNAS, theorises that even planets that are too warm, or those with atmospheres at pressures too low to host liquid water, could still support pockets of ionic liquid.
'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, an author of the study from MIT.
'Now if we include ionic liquid as a possibility, this can dramatically increase the habitability zone for all rocky worlds,' Dr Agrawal said.
On Earth, such ionic liquids are mainly only made for industries, and do not occur naturally – except for one natural case. One liquid salt is generated from the mixing of venoms produced by two rival species of ants.
In the new study, scientists sought to understand the broad conditions under which ionic liquids can be naturally produced, including the range of temperatures and pressures.
They started by mixing sulphuric acid with 30 different nitrogen-containing organic compounds across several temperatures and pressures.
Researchers then observed whether an ionic liquid formed when they evaporated away the sulphuric acid in various vials.
This work was based on previous work suggesting that some of these chemicals, considered ingredients associated with life, are surprisingly stable in sulphuric acid.
Scientists also mixed the ingredients onto basalt rocks, which are known to exist on the surface of many rocky planets.
'We were just astonished that the ionic liquid forms under so many different conditions,' says Sara Seager, another author of the study.
'If you put the sulphuric acid and the organic on a rock, the excess sulphuric 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,' Dr Seager says.
Researchers found that their reactions produced ionic liquid at temperatures up to 180 degrees Celsius and at extremely low pressures – much lower than that of the Earth's atmosphere.
The findings suggest ionic liquids can naturally form on other planets where liquid water cannot exist, under the right conditions.
'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 sulphuric acid, formed from volcanic outgassing,' Dr Seager said.
'This sulphuric acid has to flow over a little pocket of organics. And organic deposits are extremely common in the solar system,' she explained.
Scientists hope to conduct further studies to see what life-signature molecules might survive and thrive in ionic liquids.
'We just opened up a Pandora's box of new research. It's been a real journey,' Dr Seager said.
