Mystery behind red streaks on Europa's surface could now be solved

The mystery behind the striking red streaks that crisscross the surface of Europa, one of Jupiter's moons, may have been solved according to a new study published in the journal Proceedings of the National Academy of Sciences on February 20.

Scientists have long suspected these streaks result from a frozen mixture of water and salts. However, their chemical composition is mysterious, as it does not match any known Earthly substance.

A team led by the University of Washington has lab-grown a novel kind of solid crystal formed by combining table salt and water under extremely low pressure and temperature. They believe this is what most likely grows at the top and bottom of these worlds' deep oceans.

With three upcoming missions to explore Jupiter's icy moons, knowing what chemicals these missions will encounter could help better target their hunt for signs of life.

What are the red lines on Europa?

"It's rare nowadays to have fundamental discoveries in science," said Baptiste Journaux in a press release, one of the lead authors. "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," he added.

A hydrate is a rigid, salted, icy lattice that forms at low temperatures and is kept together by hydrogen bonding. The sole sodium chloride hydrate previously known had a straightforward composition; one salt molecule for every two water molecules.

In the new experiment, a small amount of salty water was squeezed between two diamonds roughly the size of a sand grain to a pressure of 25,000 times that of atmospheric pressure. The team could observe the procedure under a microscope due to the transparency of the diamonds.

The resultant two hydrates are remarkably different; one has two sodium for every 17 water molecules, and the other has one sodium chloride for every 13 water molecules. This would account for why the signals from the moons of Jupiter are more "watery" than anticipated.

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

Such cold, high-pressure conditions achieved in the lab would be typical on Jupiter's moons, where 5 to 10 kilometers of ice cover seas up to several hundred kilometers thick, with even denser types of ice likely at the bottom.

New varieties of salty ice have implications not just for planetary science. Journaux highlighted that the new substances are also relevant for physical chemistry and energy research, which uses hydrates as a form of energy storage.