For years scientists have wondered about the composition of bands of dark material on Jupiter’s frozen moon Europa. Now researchers at NASA’s Jet Propulsion Laboratory (JPL) believe that they have identified the substance as sea salt, exposed to radiation.

If the JPL team is correct, it would suggest that the ocean is interacting with the seafloor of Europa which is a positive sign for those hoping to find life there.

“We have many questions about Europa, the most important and most difficult to answer being is there life? Research like this is important because it focuses on questions we can definitively answer, like whether or not Europa is inhabitable. Once we have those answers, we can tackle the bigger question about life in the ocean beneath Europa’s ice shell,” said Curt Niebur, Outer Planets Program scientist at NASA Headquarters in Washington in a statement.

The dark material has been observed in fractures in the surface and other young geological features, this suggests that the material came from inside Europa rather than being deposited there. However, without the ability to actually sample the material scientists could only guess about its composition.

“If it’s just salt from the ocean below, that would be a simple and elegant solution for what the dark, mysterious material is,” said research lead Kevin Hand, a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.

Hand and Robert Carlson, are co-authors of a paper accepted for publication in the journal Geophysical Research Letters.

To identify the substance the researchers created an artificial Europa environment in a laboratory apparatus. Various substances, representing possible elements found on Europa, were placed in the environment and their chemical fingerprints were taken. These fingerprints, or spectra, are obtained by capturing the light reflected off of the substances.

“We call it our ‘Europa in a can. The lab setup mimics conditions on Europa’s surface in terms of temperature, pressure and radiation exposure. The spectra of these materials can then be compared to those collected by spacecraft and telescopes,” said Hand.

Scientists know that Europa’s surface is exposed to high levels of radiation created by Jupiter’s magnetic field. “Electrons and ions slam into the moon’s surface with the intensity of a particle accelerator,” according to NASA.

In addition to being exposed to high levels of radiation, conditions in the “Europa in a Can” device were kept incredibly cold, with temperatures set at minus 280 degrees Fahrenheit. Substances were placed in the environment for tens of hours, which is the equivalent of a century on Europa, according to the team.

Salt samples started out white but slowly turned a yellowish brown color in the chamber. Once this happened the spectra closely resembled the dark fractures noted on Europa.

”This work tells us the chemical signature of radiation-baked sodium chloride is a compelling match to spacecraft data for Europa’s mystery material,” said Hand.

The team also noted that the longer the salts were exposed to radiation, the darker they became. This could provide information about the age of some of Europa’s geological features.

If the researchers are correct and Europa is interacting with the rocky floor it could be a very positive sign for those looking for life. Scientists have long suspected that life on Earth began in hydrothermal vents on the ocean floor.

A recent study seems to confirm that idea. Researchers examined the interaction of minerals from the rocks inside the vents and chemicals contained in the water and found conditions and interactions which could have created simple, single celled life forms.

“There is a lot of speculation that hydrothermal vents could be the location where life on Earth began. There is a lot of CO2 dissolved in the water, which could provide the carbon that the chemistry of living organisms is based on, and there is plenty of energy, because the water is hot and turbulent. What our research proves is that these vents also have the chemical properties that encourage these molecules to recombine into molecules usually associated with living organisms,” said Nora de Leeuw, the leader of that study.

An uncrewed mission to Europa is currently being planned by NASA. According to the agency, if all goes well, the Europa Clipper could be ready for launch as early as 2022.