Mysterious dark material on Jupiter's moon Europa could be sea salt: NASA

Mysterious dark material on the surface of Jupiter's moon Europa is likely sea salt from a subsurface ocean, darkened by exposure to radiation, researchers from the U.S. space agency NASA suggested Tuesday.

For more than a decade, scientists have wondered about the nature of the dark material that coats long, linear fractures and other relatively young geological features on Europa's surface.

Its association with young terrains suggests the material has erupted from within Europa, but with limited data available, the material's chemical composition has remained elusive.

To identify the dark material, researchers at NASA's Jet Propulsion Laboratory created a lab setup that mimics conditions on Europa's surface in terms of temperature, pressure and radiation exposure.

For this study, the researchers tested samples of common salt -- sodium chloride -- along with mixtures of salt and water, in their vacuum chamber in accordance with Europa's chilly surface temperature of minus 280 degrees Fahrenheit (minus 173 degrees Celsius).

They then bombarded the salty samples with an electron beam to simulate the intense radiation on the moon's surface.

After several days of exposure to this harsh environment, which corresponds to as long as a century on Europa, the salt samples' color turned from white to yellowish-brown, which is similar to features on the icy moon.

Additionally, the longer the samples were exposed to radiation, the darker the resulting color, they found.

"The presence of sea salt on Europa's surface suggests the ocean is interacting with its rocky seafloor -- an important consideration in determining whether the icy moon could support life," NASA said in a statement.

The study was published online in the U.S. journal Geophysical Research Letters.