Forget drilling through the ice – Europa’s buried ocean might come to us. In a cracked region of Jupiter’s frozen moon (pictured below), salty ice has been spotted that doesn’t match anything seen before.

Europa has been a perennial favourite in the search for alien life, thanks to its probable subsurface ocean. NASA plans to send a probe to the moon to study its surface in the 2020s, but what we are learning in the meantime is making it an even more attractive destination.

Infrared observations from the Galileo spacecraft, which visited the Jupiter system in the 1990s, found that the moon is covered in water ice. Sulphur and oxygen from volcanoes on the nearby moon Io also fall onto Europa’s surface, where they combine to make magnesium sulphate – the same chemical found in Epsom salts.


Now a new analysis has found another, unidentified material that only shows up in fractured terrain. This could mean the buried ocean is breaching the surface.

The spectrum of the material – its chemical signature – has so far defied identification. “It looks like the spectrum of water ice except that it’s distorted,” says Patrick Fischer of the California Institute of Technology. The team hasn’t been able to reproduce it using a library of known chemicals – although they can rule out sulphates, which Europa researchers expected to see.

One possibility is an unknown blend of potassium or sodium chloride, which would mean these regions are salt flats left behind when ocean water burbled up and then evaporated, giving us a look at the chemistry hidden within. “We can guess that the spectrum we’re seeing is probably evaporate deposits of salt left over from the ocean,” Fischer says.

If that’s true, there are big implications for Europa’s habitability. If the ocean is seasoned with those chloride salts instead of the sulphate salts expected, its overall salinity could be three times lower than thought, making it friendlier to life.

“Any information on the salt content of the oceans helps us understand what biology might be possible,” says Christopher Chyba of Princeton University.

Life-friendly

“Microbial life on Earth can live in high salt concentrations, but it comes at a cost,” he says. “These new observational results make Europa look slightly better from the point of view of the origin of life on Europa and, should life actually exist there, slightly less challenging for microbes to live in the ocean.”

And if ocean chemistry is laid bare on the surface, we could see if any of the chemicals that fuel chemosynthetic ecosystems on Earth are present – improving the chances of finding ocean life.

Long before NASA’s mission arrives, we should know more. Fischer’s team is busy writing proposals to get better spectral data from Europa that will classify the mystery material. At the same time, researchers at the nearby Jet Propulsion Lab are trying to manufacture an ice with a similar spectrum in the lab.

But these faint hints underscore the need to take a close look at Europa, says Chyba.

“I admire the wonderful work that the Caltech/JPL group has done,” he says. “But their paper is also a reminder of how badly we need a dedicated mission to Europa.”

Journal reference: Astronomical Journal, in press

Image credits: NASA/JPL-Caltech/SETI Institute; NASA/JPL/University of Arizona