Salt water As on the Earth's oceans has been seen on Europa. Another good reason why we really need to visit this place

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The moon of Jupiter Europa is an intriguing world. It is the smoothest body in the solar system and the sixth largest moon in the solar system, although it is the smallest of the four Galilean moons. The most intriguing of all is Europa's underwater ocean and its potential for livability.

The scientific consensus is that Europa has an ocean below the surface under its exceptionally smooth and icy surface. It is estimated that the thickness of the crust is between 10 and 30 km, and the depth of the ocean could be about 100 km (60 mi). If this is true, the volume of Europa's oceans is about two to three times that of the Earth's oceans.

Two models from inside Europe. Most of the scientists who studied Europa prefer the Liquid Ocean model to the ice convection model. Image: NASA / JPL.
Two models from inside Europe. Most of the scientists who studied Europa favor the Liquid Ocean model over the ice convection model. Image: NASA / JPL.

The interior of Europe is kept warm by the warming of the tides and possibly by the radioactive decay of elements lying in its rocky mantle. But studies show that radioactive decay is not enough to produce heat in Europe. Whatever the exact source of heat, just create an ocean underwater.

It is probably an ocean of salt water, which is important for livability. Initially, scientists thought that salinity came from magnesium chloride, which is essentially an Epsom salt. But a new study by scientists at Caltech / JPL shows that it may not be magnesium chloride, but sodium chloride, the same type of salt that makes the Earth's oceans salty.

The new study is called "Sodium Chloride on Europa's Surface" and was published in the June 12 issue of Science Advances. The authors are Samantha Trumbo, Michael Brown and Kevin Hand. Trumbo is the main author of the document.

The discovery comes from Hubble's observations of the surface of Europe. There are yellowish areas on the surface of the moon that have remained somewhat mysterious.

A composite color view of Europa. The natural color image is on the left, and the enhanced color image used to highlight the differences on the surface of the moon. The white and blue areas correspond to the water ice, the brownish red zones to the hydrated salts. In 1997, when the Galileo probe captured these images, the yellow areas were not identified. A new study indicates that the yellow areas consist of sodium chloride from the ocean underwater. Image Credit: By NASA / JPL / University of Arizona - http://photojournal.jpl.nasa.gov/catalog/PIA01295 (image link), Public Domain, https: // commons. wikimedia.org/w/index.php? curid = 10705462
A composite color view of Europa. The natural color image is on the left, and the enhanced color image used to highlight the differences on the surface of the moon. The white and blue areas correspond to the water ice, the brownish red zones to the hydrated salts. In 1997, when the Galileo probe captured these images, the yellow areas were not identified. A new study indicates that the yellow areas consist of sodium chloride from the ocean underwater. Image Credit: By NASA / JPL / University of Arizona – http://photojournal.jpl.nasa.gov/catalog/PIA01295 (image link), Public Domain, https: // commons. wikimedia.org/w/index.php? curid = 10705462

The surface of the Europa is a geologically young ice shell. So all that is on the surface is probably from the ocean below. That's what led scientists to think there was an ocean below. An ocean rich in sulphate salts.

But new spectral data from the Keck Observatory suggest that the salts on the surface are not magnesium sulphates. The absorption lines indicating the presence of magnesium sulphates were absent from the Keck data. These types of salts have very different absorption lines and they just were not there. Scientists thought that they could see sodium chloride on the surface, but the problem is that sodium chloride does not become known in the infrared.

"We thought we might be seeing sodium chlorides, but they are essentially devoid of any functions in the infrared spectrum," says Mike Brown, a global astronomy professor Richard and Barbara Rosenberg at Caltech and co-author of the book. Progress of science paper.

But a colleague from Brown, and possibly co-author of the new paper, had a glimpse of the problem.

"Sodium chloride, it's a bit like invisible ink …"

Kevin Hand, JPL, co-author.

He's called Kevin Hand from JPL. He had irradiated ocean salts in a laboratory, under conditions similar to those in Europe. He found that after irradiation, sodium chloride was revealed in visible light by changing color. The color has changed to? You guessed it: yellow. Just like in the yellow region on the surface of Europe, named Tara Regio.

"Sodium chloride is a bit like invisible ink on Europa's surface. Before irradiation, we can not say that it is there, but after irradiation, the color is obvious, "says Hand, a scientist and scientist at JPL, co-author of the book. Progress of science paper.

"Nobody had used Europa's visible wavelength spectra before, which had this type of spatial and spectral resolution. the Galilee Spaceship did not have a visible spectrometer. There was just a spectrometer in the infrared, "says Samantha Trumbo, graduate student of Caltech, lead author of the article.

Images from NASA's Galileo spacecraft show the intricate details of Europa's icy surface. The dark streaks on the surface of the moon are called linae. Their most likely explanation is that the crust is very active in the Earth 's image, and as the crust moves, warmer ice and water move up from the subsoil. Image: NASA / JPL-Caltech

The trio of scientists then turned to the Hubble Space Telescope to advance the idea. They directed the Hubble towards Europa and found an absorption line in the visible spectrum perfectly adapted to the irradiated salt. This confirmed the presence of irradiated sodium chloride on Europa. And the likely source of this is the ocean underwater.

"We have had the ability to do this analysis with the Hubble Space Telescope for 20 years," said Brown. "It's just that no one has thought of looking."

This is solid evidence to support an ocean underwater with sodium chloride as the oceans of the Earth. But it's not a slam dunk. It could be evidence of different materials in the ice crust.

Europa is a seductive target in the search for life. Its ocean below the surface only needs to be explored. There have been many suggestions on how to do this. This is an artistic interpretation of the Europa "tunnelbot", a nuclear-powered conceptual craft capable of penetrating the icy crust of the moon. (Credit: Alexander Pawlusik, LERCIP Internship Program, NASA Glenn Research Center)
Europa is a seductive target in the search for life. Its ocean below the surface only needs to be explored. There have been many suggestions on how to do this. This is an artistic interpretation of the Europa "tunnelbot", a nuclear-powered conceptual craft capable of penetrating the icy crust of the moon. (Credit: Alexander Pawlusik, LERCIP Internship Program, NASA Glenn Research Center)

In any case, the study presents more intrigues around Europa.

As the authors say at the end of their paper, "that the observed NaCl is directly related to the composition of the ocean, its presence deserves a reassessment of our understanding of the geochemistry of Europe".

If the salt in the ocean is magnesium sulphate, it could have penetrated into the ocean by the rocks of the ocean floor. But if it's sodium chloride, that's another story.

"Magnesium sulphate would have simply seeped into the ocean from the rocks of the ocean floor, but sodium chloride could indicate that the ocean floor is hydrothermally active," says Trumbo. "This would mean that Europa is a planetary body more geologically interesting than previously thought."

Launch the rockets. Let's find out!

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