This is why it is so huge that the moon of Jupiter Europa is covered with salt

Thanks to the Hubble telescope's far-reaching optics and intelligent spectral analysis in visible light, scientists have detected what looks a lot like sodium chloride – or good old table salt – on Jupiter's moon, Europa.

This means that the salty ocean hidden just below the surface of this moon might look more like the Earth's oceans than we previously thought; this also challenges our current understanding of the geological composition of Europa.

Previously, the NASA Voyager and Galileo probes had already strongly suggested the presence of a salty liquid ocean under an ice-cold shell on Europa, but it was thought that the salt in question was based on magnesium sulfate, such as salt. Epsom.

A change in the analytical techniques led to the new discovery. In this case, scientists used a spectrometer focusing on the visible spectrum of light rather than the infrared spectrum, as well as high resolution images of Hubble.

"Nobody had ever used the visible wavelength spectra of Europe before such a spatial and spectral resolution," says lead author of the new study, Samantha Trumbo, a specialist in Planetary Science, California Institute of Technology (Caltech).

"The Galileo probe did not have a visible spectrometer, it only had a near-infrared spectrometer and, in the near infrared, the chlorides are peculiar."

Higher quality images from the W. Keck observatory had already hinted that sodium chloride might be present, but obtaining additional evidence over vast expanses of space was not a simple process.

The researchers relied on earlier work in 2017, in which sodium chloride placed under conditions similar to those of Europa in the laboratory showed chemical changes likely to make it appear on a visible light spectrometer.

Armed with this information, the team used the Space Telescope Imaging Spectrograph (STIS) aboard Hubble and was able to detect traces of irradiated table salt compounds in the visible spectrum at 450 nanometers; this corresponded to laboratory tests.

Europa conditions are simulated in the laboratory. (NASA / JPL-Caltech)

"Sodium chloride is a bit like invisible ink on the surface of Europa," says astrobiologist Kevin Hand of NASA's reaction propulsion laboratory, who worked on the experiments of 2017 and on this new study.

"Before irradiation, you can not say that it is there, but after irradiation, the color is obvious to you."

The results do not count as a definitive guarantee that the Europa basement is filled with table salt, but researchers have been able to spot it in areas where surface ice had been broken – possibly allowing bottom materials to go up .

It's enough to re-evaluate what the hidden ocean of Europe is, say the scientists behind the new study, and the kind of life it could potentially harbor.

"Magnesium sulphate would have simply infiltrated into the ocean rocks from the bottom of the ocean, but sodium chloride could indicate that the bottom of the ocean is hydrothermally active", said Trumbo.

"This would mean that Europa is a planetary body more geologically interesting than previously thought."

The good news is that the NASA Europa Clipper probe should be launched in the 2020s and will make no less than 45 Europa passes. It should be a new mine of information that scientists and salt researchers can find.

It is also further proof of how the collection of new data and the use of new techniques can improve our understanding of the Universe at large, even years or even decades after the first observations.

The search was published in Progress of science.