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The huge ocean sliding under the ice shell of the Jupiter moon Europa may be intriguing similar to the seas of the Earth, suggests a new study.
Scientists have generally thought that sulfate salts dominated The underwater ocean of Europe, which contains about twice as much water as all the seas on the planet. But the Hubble Space Telescope has detected the probable presence of sodium chloride (NaCl) on the icy surface of Europa, the study says.
The NaCl – the same substance that makes up the old regular table salt – probably comes from the ocean, said members of the study team. And it's quite exciting, since the salinity of the Earth's oceans comes mainly from NaCl.
Related: Photos: Europa, the mysterious frozen moon of Jupiter
"We need to revisit our understanding of Europa's surface composition, as well as its internal geochemistry," told Space.com senior author Samantha Trumbo, of the California Institute of Technology in Pasadena.
"If this sodium chloride really reflects the internal composition, then [Europa’s ocean] could be more like Earth than we thought, "she added.
From NASA Galileo Spaceship, 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 suggest 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 bombarded.)
Trumbo and his colleagues went to search for signs of NaCl on Europa. They used Hubble's Space Telescope Imager (STIS) instrument during four series of observations, from May 2017 to August 2017.
STIS spotted a line of absorption at 450 nanometers, characteristic of irradiated NaCl. But this signature has not been spread all over Europe. The team instead found it in the dominant hemisphere of the Moon, the one that constantly faces Jupiter. (Like Europa's own moon, Europa is closely linked to her mother planet, always showing her the same face.)
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.
The Europa's rear hemisphere is hammered by sulfur compounds thrown out by another of Jupiter's many moons, the superolcanic 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 "may better represent that of Europa's endogenous material," wrote Trumbo and his colleagues in the study published online today in the journal Progress of science.
However, it's not clear if that's really the case, stressed Trumbo.
"We are convinced that 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 less active player. Indeed, experiments on the Earth suggest that oceans such as Europa's could begin to be dominated by sulphates; 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 of 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 Saturn Moon Enceladus, another frozen satellite with a sea below the surface.
Mike Wall's book on the search for extraterrestrial life, "Over there"(Grand Central Publishing, 2018, illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on twitter @Spacedotcom or Facebook.
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