The possibility of a Europa table salt ocean has intrigued scientists. A new study suggests that the huge ocean sliding under the ice shell could be very similar to the seas of the Earth.
Scientists have generally found that sulphate salts dominate because they contain about twice as much water as all the seas of the Earth. But the Hubble Space Telescope has detected the probable presence of sodium chloride (NaCl) on the icy surface of Europa, the study says.
NaCl – the same substance that makes up the good old regular table salt – probably comes from the ocean, said the study team members. And it’s quite exciting, since the salinity of the Earth’s oceans comes mainly from NaCl.
“We need to revisit our understanding of Europa’s surface composition, as well as its internal geochemistry,” senior author Samantha Trumbo of the California Institute of Technology in Pasadena told Space.com.
“If this sodium chloride really reflects the internal composition, then (the ocean of Europe) could be more similar to the Earth than we thought,” she added.
NASA, which gravitated around Jupiter from 1995 to 2003, spotted strange yellowish spots on Europa’s surface. Subsequently, laboratory experiments performed under simulated Europa surface conditions suggested that irradiated NaCl could be responsible for these “color centers”. (Europa is in Jupiter’s powerful radiation belts and the moon’s surface is then constantly bombarded.)
Trumbo and her colleagues went to search for signs of NaCl on Europa. They used Hubble’s Space Telescope Imaging Spectrograph (STIS) instrument in four rounds of observations, from May 2017 to August 2017.
STIS has identified a 450 nanometer absorption line characteristic of irradiated NaCl. But this signature has not been widespread throughout Europa. The team instead found it in the dominant hemisphere of the Moon, the one that constantly faces Jupiter.
In addition, NaCl was concentrated in the “chaotic regions” – complex, disturbed and geologically young areas of the Europan surface where materials could spring from the ocean.
Europa’s rear hemisphere is hammered by sulfur compounds released by another of Jupiter’s many moons, the supervolcanic Io. But the dominant hemisphere is immune to this cosmic rain. Thus, the composition of the young and relatively pure chaos of the ruling hemisphere “might better represent that of Europa’s endogenous material,” wrote Trumbo and hercolleagues in the study’s report.
However, it is unclear if this is really the case, said Trumbo.
“We are convinced that the sodium chloride comes from within,” she said. “But the extrapolation to” the interior is dominated by chlorides “is less certain.”
For example, it is still possible that sulphate salts – such as magnesium sulphate, commonly known as Epsom salt – prevail over the seas of Europan, with NaCl as a relatively inactive player. Indeed, experiments on the Earth suggest that oceans such as Europa’s could begin to be dominated by sulphate; If you soak meteorites in the water, the sulfates are leached, said Trumbo.
The scale can switch to NaCl over time if some geological processes prevail. For example, large hydrothermal systems in the seabed could do the trick. And Europa could have such systems; after all, they are widespread in the Earth’s oceans and probably also exist on the geyser-spewing, another icy satellite with a sea below the surface.