Table salt may be hiding in Europa’s underground sea

What flavors our food may also season the sea of Jupiter’s moon Europa.

Sulfate salts were thought to lurk in the watery ocean under the moon’s icy crust. But data from the Hubble Space Telescope suggest that common table salt dominates the sea’s chemistry, researchers report June 12 in Science Advances.

“This could mean that the ocean chemistry is more similar to what we’re used to on Earth and what we see at Enceladus, which is an ocean moon of Saturn,” says Samantha Trumbo, a graduate student in planetary sciences at Caltech.

The scientists surveyed Europa’s chaos terrain, or regions where the surface ice has been heavily disrupted, possibly by material swelling up from below. “If anywhere was going to represent the internal composition, it would be these places,” Trumbo says.

Data from the Galileo mission in the 1990s had suggested a hidden sea containing salts, suspected to be sulfates. But later studies on infrared light reflected from Europa failed to find chemical signatures for sulfates originating in the ocean. New data from Hubble homed in on Europa’s visible spectrum and revealed that the chaos terrain of one of the moon’s hemispheres contains the fingerprint of irradiated sodium chloride.

When electrons crash into sodium chloride, as is thought to happen on Europa, the collision ejects chloride ions. Electrons fill these vacancies in the salt, changing its color from white to a yellowish hue. That color matches what’s seen in some of the moon’s rough patches.

Liquid water is thought to be essential for life. If Europa’s ocean turns out to be more similar to Earth’s than was thought, that could raise tantalizing questions about the moon’s ability to support life. “People think that, if there were a place elsewhere in the solar system where there might be life, Europa is a candidate,” Trumbo says.