A new form of ice based on water and sodium chloride (table salt), created in the laboratory at low temperatures and high pressure, could be what exists in the red streaks that cross the surface of Europa, one of Jupiter’s moons .
A study published today by Pnas coordinated by the University of Washington describes this new type of ice that the team estimates is what could form on the surface and bottom of the deep oceans of some icy moons.
Europa’s surface is streaked with red streaks that scientists suspect are a frozen mixture of water and saltsbut its chemical signature is mysterious because it doesn’t match any known substance on Earth.
Salt and water are known «very well under terrestrial conditions, but beyond that, we are totally in the dark and now we have these planetary objects that probably have compounds that are very familiar to us, but in very exotic conditions,» says Baptiste Journaux. from the University of Washington.
The discovery of new types of salty ice is important not only for planetary science, but also for physical chemistry and even for energy research, which uses hydrates for energy storage, says the researcher.
At low temperatures, water and salts combine to form a rigid framework of salty ice, known as a hydrate, which is held in place by hydrogen bonding. The only sodium chloride hydrate known so far was a simple structure with one molecule of salt for every two of water.
But the two new hydrates, found at moderate pressures and low temperaturesthey are strikingly different, the university notes.
One has two sodium chlorides for every 17 water molecules; the other has one sodium chloride for every 13 molecules of water. This would explain why the signatures on the surface of Jupiter’s moons are more «watery» than expected, adds the researcher.
The team tried to measure how the addition of salt would change the amount of ice that could be obtained, since this mineral acts as antifreeze, but when they put it under pressure they saw crystals start up that they did not expect. “It was a very serendipitous discovery,” according to Journaux.
The experiment consisted of compressing some salt water between two diamonds the size of a grain of sand, squeezing the liquid up to 25,000 times standard atmospheric pressure.
The cold, high-pressure conditions created in the laboratory would be common on Jupiter’s moons, where scientists believe that between five and ten kilometers of ice would cover oceans up to several hundred kilometers thick, with even denser ice forms possible at the bottom.
«Pressure pushes the molecules closer together, so their interaction changes, and that’s the main driver of the diversity of crystal structures we’ve found,» explains Journaux. That form of stable ice stays at standard pressure down to about minus 50 degrees, so if there’s a very brackish lake, say in Antarctica, that could be exposed to these temperatures, this newly discovered hydrate could be present there, given.
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The team hopes to make or collect a larger sample that will allow for a more complete analysis and verify if the signatures of the icy moons match those of the newly discovered hydrates.
The icy moons of Jupiter are the next target of two space missions: Juicy, from the European Space Agency (ESA) will launch in April to study the planet and three of its satellites, Ganymede, Callisto and Europa, which could hide oceans under their Surface Next year it will be NASA’s Clipper’s turn to head to Europa.