New type of salty ice may exist on extraterrestrial ocean moons

By Ashley Strickland, CNN

The mysterious red streaks crisscrossing the surface of Jupiter’s moon Europa may be the result of a newly discovered kind of salty ice.

Europa has long intrigued scientists because the moon has a subsurface ocean beneath a thick shell of ice. Plumes of water have been known to erupt from cracks in the ice shell, releasing the contents of the moon’s alien ocean into space.

Ocean worlds like Europa are the best bet for finding evidence of life outside of Earth, according to scientists.

The chemical signature of Europa’s surface red streaks, thought to be a frozen mix of water and salts, seemed unusual because it didn’t match any known substance on Earth.

Scientists determined in 2019 that the yellow portions of Europa’s surface were caused by the presence of sodium chloride — better known as table salt.

To unlock more insight into Europa, which will be visited by the European Space Agency’s JUICE (short for the Jupiter Icy Moons Explorer) mission and NASA’s Europa Clipper mission within the next couple of years, scientists worked to recreate the moon’s conditions in a lab.

The research team found that combining water, table salt, cold temperatures and high pressure resulted in a new type of solid crystal — and this substance could exist on Europa’s surface and at the bottom of its hidden ocean.

“It’s rare nowadays to have fundamental discoveries in science,” said lead study author Baptiste Journaux, an acting assistant professor of Earth and space sciences at the University of Washington, in a statement.

“Salt and water are very well known (in) Earth conditions. But beyond that, we’re 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. We have to redo all the fundamental mineralogical science that people did in the 1800s, but at high pressure and low temperature. It is an exciting time.”

Water and salts create a hydrate, a rigid icy lattice supported by hydrogen bonds, in cold temperatures.

Unusual compound with two salt molecules

Before this study, prevailing scientific wisdom stated there was only one hydrate for sodium chloride, created by two water molecules and one salt molecule.

After the study experiment, the researchers discovered two new hydrates — one utilizing two salt molecules for every 17 water molecules, and another with one salt molecule for every 13 molecules.

“It has the structure that planetary scientists have been waiting for,” Journaux said.

A study detailing the findings was published Monday in the Proceedings of the National Academy of Sciences.

The hydrates might explain why the chemical signatures of Jupiter’s ocean worlds are so “watery,” according to the study.

The researchers began their experiment by compressing a small amount of salty water between two diamonds that were each about the size of a grain of sand. The water was squeezed up to 25,000 times the standard atmospheric pressure.

The team was able to observe this process through a microscope.

“We were trying to measure how adding salt would change the amount of ice we could get, since salt acts as an antifreeze,” Baptiste said. “Surprisingly, when we put the pressure on, what we saw is that these crystals that we were not expecting started growing. It was a very serendipitous discovery.”

Frozen, high-pressure environment

Jupiter’s ocean moons likely experience similar conditions with icy temperatures and high pressure.

The ice shell that makes up Europa’s surface is estimated to be between 10 and 15 miles (16 and 24 kilometers) thick, and the ocean it likely sits atop is estimated to be 40 to 100 miles (64 to 161 kilometers) deep.

“Pressure just gets the molecules closer together, so their interaction changes — that is the main engine for diversity in the crystal structures we found,” Journaux said.

Of the two hydrates, one remained stable even after the pressure was released.

“We determined that it remains stable at standard pressure up to about minus 50 Celsius (minus 58 degrees Fahrenheit). So if you have a very briny lake, for example in Antarctica, that could be exposed to these temperatures, this newly discovered hydrate could be present there,” Journaux said.

Understanding the chemistry present on ocean worlds like Europa will allow scientists to better understand the data collected by missions like JUICE and Europa Clipper in the future.

“These are the only planetary bodies, other than Earth, where liquid water is stable at geological timescales, which is crucial for the emergence and development of life,” Journaux said.

“They are, in my opinion, the best place in our solar system to discover extraterrestrial life, so we need to study their exotic oceans and interiors to better understand how they formed, evolved and can retain liquid water in cold regions of the solar system, so far away from the sun.”

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