(ORDO NEWS) — Two newly discovered forms of frozen salt water could help scientists unravel the mystery of the solar system’s ice-covered moons.
Under the influence of higher pressures and lower temperatures than those found naturally on Earth, the atoms in hydrated sodium chloride, more commonly known as water ice salt, have organized themselves into never-before-identified structures in which the proportion of water molecules is much higher than that of salt.
This may explain the strange chemistry on the surface of Jupiter’s moon Europa, which appears to be more watery than scientists expect.
“Fundamental discoveries rarely happen in science these days,” says Earth scientist and astronaut Baptiste Journo of the University of Washington.
“Salt and water are very well known in terrestrial conditions. But then we are completely ignorant.
And now we have these planetary objects that probably have conjunctions that are very familiar to us, but in very exotic settings.
We have to redo all the basic mineralogical science that people did in the 1800s, but at high pressure and low temperature. It’s an exciting time.”
Salt and water, also known as sodium chloride and dihydrogen oxide, are abundant in our home world. When mixed, salt molecules dissolve in water molecules, forming a solution.
The presence of salt lowers the freezing point of the solution compared to unsalted water, but as the temperature continues to drop under typical terrestrial atmospheric conditions, the solution will eventually freeze.
When this happens, the molecules settle into a rigid lattice structure known as a hydrate. On Earth (outside the lab), this structure has only one configuration: one molecule of salt for every two molecules of water.
On satellites such as Europa and Ganymede, which revolve around Jupiter, and Saturn’s moon Enceladus, scientists also found evidence of the presence of salt and water, only the conditions in which they are located are very different from those on Earth.
Exposed to the near vacuum of space, away from the Sun, the surfaces of these distant worlds can become extremely cold.
Beneath their ice sheets lie oceans that, in some cases, can be more than 100 times thicker than the deepest waters on Earth, creating quite extreme pressures and temperatures.
Journot and his colleagues decided to investigate the effect of salt on ice production.
They compressed a tiny ball of salt water in a diamond anvil cell under extremely cold conditions, creating a pressure 25,000 times Earth’s atmospheric pressure, while lowering the temperature to -123 degrees Celsius (-190 degrees Fahrenheit).
They didn’t expect what would happen next.
“We were trying to measure how adding salt would change the amount of ice we could get since the salt acts like an antifreeze,” Journeau explains.
“Surprisingly, when we pressed, we saw that these crystals, which we did not expect, began to grow. It was a very successful discovery.”
Under the conditions of their experiment, the researchers saw two new arrangements of salt and water molecules.
In one of them, for every 17 molecules of water, there were two molecules of salt; in another, there were 13 water molecules per molecule of salt.
Both are very different from the one-and-two salt water seen naturally on Earth, and are consistent with the watery chemical signatures seen on icy moons.
“It has the structure that planetary scientists have been waiting for,” Journeau adds.
The main factor, according to the researchers, is the pressure that squeezes the molecules together and forces them to look for new ways to coexist.
But even when the pressure was released, one of the newly identified hydrates – the one with 17 water molecules – remained stable down to -50 degrees Celsius.
This suggests that it can also be found here on Earth, possibly under the ice of Antarctica.
Further research is needed to determine if this discovery can solve the mystery of the icy moon.
“The infrared spectra of [the hydrate] are yet to be determined in future studies,” the researchers write, “but its hyperhydrated structure may solve the longstanding mystery of the unidentified hydrate phase on the surface of Europa and Ganymede.”
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