Salt exists on Earth's oceans in great quantities, but new evidence points to its presence in Jupiter's moon Europa as well.
Specifically, scientists have discovered that sodium chloride — which is just ordinary table salt — is on the surface of Europa and may be derived from the icy moon's subsurface ocean.
In a new study published in the journal Science Advances, scientists from Caltech and the Jet Propulsion Laboratory used visible light spectral analysis to determine that the yellow color detected on certain parts of the moon's surface is actually sodium chloride.
Sodium chloride, which is commonly known as table salt, is the primary component of the Earth's oceans. The findings suggest that Europa's hidden oceans may be chemically similar to Earth's own oceans.
Finding Salt In The Cosmos
Previous analysis of flyby missions have revealed that there's a layer of salty liquid water beneath Europa's frozen shell. The infrared spectrometer on the Galileo spacecraft didn't just find water ice on the surface of the moon, but also magnesium sulfate salts, which are like the Epsom salts used in soak baths.
Due to Europa's young age geologically and the evidence of past geologic activity, it was suspected that the salts found on the surface are derived from the ocean underneath. After all, many scientists already suspect an ocean composed primarily of sulfate salts.
However, it turns out that this conclusion isn't quite right.
Table Salt In Europa
New, higher spectral resolution data from the W. M. Keck Observatory showed that the previous researchers haven't been looking at magnesium sulfates after all.
"We thought that we might be seeing sodium chlorides, but they are essentially featureless in an infrared spectrum," said coauthor Mike Brown of Caltech in a statement.
Fortunately, Kevin Hand at JPL found that salts change colors after irradiation, which could be seen with an analysis of visible spectrum. Sodium chloride turns into a distinct shade of yellow similar to that seen in Europa's region known as Tara Regio.
With the Hubble Space Telescope, the study authors identified a distinct absorption in the visible spectrum at 450 nanometers, which matched the irradiated salt. This confirmed that Tara Regio's yellow hue reflected the existence of sodium chloride on its surface.
"Sodium chloride is a bit like invisible ink on Europa's surface," Hand explained. "Before irradiation, you can't tell it's there, but after irradiation, the color jumps right out at you."
Of course, the presence of sodium chloride on the surface doesn't automatically mean that it was derived from the subsurface ocean. Still, the findings are enough to warrant a closer look at Europa's geochemistry.
As lead author Samantha Trumbo pointed out, sodium chloride may mean that the moon's ocean floor is hydrothermally active — and this would make Europa significantly more interesting to scientists.
