Saline colors Europe yellow

Subglacial ocean of Jupiter's moon could be more similar to our seas than thought

The yellowish hue of some areas of Jupiter's moon Europa is due to saline, as evidenced by spectral data from the Hubble telescope. © NASA / JPL / University of Arizona
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Surprising discovery: On Jupiter's moon Europa, there are obviously not only sulfur salts, but also plenty of table salt. This is indicated by spectral measurements of the Hubble Space Telescope. The sodium chloride not only dyes the crust yellowish, it also makes the ocean of Jupiter's moon more similar to our seas than previously thought - and increases the chance of extraterrestrial life.

Jupiter's moon Europa is considered the most promising candidate for extraterrestrial life in our solar system. For under its kilometer-thick ice crust lies salty ocean, which is kept fluid and in motion by the magnetic field and tidal forces of nearby Jupiter, but also by the heat of the rocky core. Steam fountains and the tectonics of the ice crust could also provide mass transfer between the ocean and the surface.

Manhunt for the salt

However, it was unclear what makes the water in Europe's subglacial ocean salty. Data from the infrared spectrometer of the Galileo spacecraft indicated that especially salts of salts could shape the ice and the ocean. However, recent observations with earth-based telescopes have raised doubts. That's why Samantha Trumbo of the California Institute of Technology and her colleagues have set their sights on Jupiter's moon Europa with the Hubble Space Telescope.

"So far, no one has detected such high-resolution spectral data from Europe in the visible range of light, " says co-author Kevin Hand of NASA's Jet Propulsion Laboratory (JPL). Although this has been possible for 20 years, but it just did not do it. "Traditionally, it was assumed that the interesting spectrometer data from planetary surfaces are all in the infrared because most of the relevant molecules show their fundamental features."

Signature of irradiated salt

But just an exciting molecule remains hidden in the infrared spectra: sodium chloride. "Alkali chlorides are spectrally inconspicuous in the infrared, but when they are under particle bombardment, they develop clearly visible lines in the visible wavelength range, " explain the researchers. "Sodium chloride is a bit like secret ink: you do not see it before the radiation, but after that you can not miss the color." Display

Because the surface ice of Europe is constantly struck by radiation and particles, these signatures should be detectable - if common salt is present. And indeed, when Trumbo and her team evaluated the Hubble spectra, the characteristic signature of sodium chloride was revealed. "We observe a broad absorption near 450 nanometers, which agrees well with the absorption of irradiated sodium chloride, " the scientists report. According to this, there must be cooking salt on Jupiter's moon Europa.

Yellow spots and hydrothermal springs

Interesting too: The saline signature is not evenly distributed on the Jupiter's moon, but focuses wherever the ice crust is particularly young. Sodium chloride is particularly abundant in the Tara region of Europe's leading hemisphere, according to the researchers. In this area, the ice surface appears strikingly yellowish - a coloration that could have come from the salt that has been changed by irradiation.

According to Trumbo and her team, this distribution suggests that sodium chloride is also present in the subglacial ocean and has risen to the surface with rising water vapor and young ice. "The presence of sodium chloride could be an indication that the cause of Europe's ocean is hydrothermally active, " says Trumbo. "That would make Europe a geologically even more exciting celestial body than already accepted."

Life under the ice?

However, the new insights into possible alien life in Europe are particularly exciting. For with the sea salted by sodium chloride and the hydrothermal vents on the ocean floor, the subglacial ocean of Jupiter's moon is similar to the primordial seas on earth. On our planet, the first life could have come from such hot, undersea sources.

The parallels therefore raise the hope that perhaps even under the ice crust of Europe simple organisms could live. Future space probes to land on Jupiter's moon could answer that question. (Science Advances, 2019; doi: 10.1126 / sciadv.aaw7123)

Source: California Institute of Technology

- Nadja Podbregar