Table salt compound spotted on Jupiter's moon

Researchers have discovered that the visible yellow pattern on the surface of Jupiter's moon -- Europa -- is actually sodium chloride, an ingredient we use on a daily basis.

Using a visible light spectral analysis, planetary scientists have discovered that the yellow colour visible on portions of the surface of Europa is table salt, which is also the principal component of sea salt.

Flybys from the Voyager and Galileo spacecraft have led scientists to conclude that Europa is covered by a layer of salty liquid water encased by an icy shell, according to the study published in the Journal of Science Advances.

Galileo carried an infrared spectrometer, instrument scientists use to examine the composition of the surface they are examining. Galileo's spectrometer found water ice and a substance that appeared to be magnesium sulfate salts like Epsom salts, which are used in soaking baths.

Since the icy shell is geologically young and features abundant evidence of past geologic activity, it was suspected that whatever salts exist on the surface may derive from the ocean below. As such, scientists have long suspected an ocean composition rich in sulfate salts.

That all changed when new, higher spectral resolution data suggested that the scientists weren't actually seeing magnesium sulfates on Europa.

"We thought that we might be seeing sodium chlorides, but they are essentially featureless in an infrared spectrum," said Mike Brown, co-author of the Science Advances paper.

However, "sodium chloride is a bit like invisible ink on Europa's surface. Before irradiation, you can't tell it's there, but after irradiation, the colour jumps right out at you," said Hand, a scientist and co-author of the Science Advances paper.

"No one has taken visible wavelength spectra of Europa before that had this sort of spatial and spectral resolution. The Galileo spacecraft didn't have a visible spectrometer. It just had a near-infrared spectrometer," said Samantha Trumbo, the lead author of the paper.

While the finding does not guarantee that this sodium chloride is derived from the subsurface ocean (this could, in fact, simply be evidence of different types of materials stratified in the moon's icy shell), the study's authors propose that it warrants a reevaluation of the geochemistry of Europa.