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

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.