Table salt on Jupiter’s moon

Planetary scientists at NASA’s Jet Propulsion Laboratory found that distinct features arise in ocean salts in the visible spectrum – most notably, they turn a shade of yellow.

Using the Hubble Space Telescope to conduct a visible light spectral analysis of Europa, they identified absorption in the visible spectrum of 450nm, which matched the irradiated salt.

The key to the finings has been using a visible light spectral analysis instead of infrared. NASA’s Galileo spacecraft had previously used an near-infrared spectrometer to analyse the moon’s surface — but sodium chloride can’t be seen using near-inferred.

JPL scientist Kevin Hand said: “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.”

Mike Brown, co-author of the study published in Science Advances, said: “People have traditionally assumed that all of the interesting spectroscopy is in the infrared on planetary surfaces, because that’s where most of the molecules that scientists are looking for have their fundamental features.”

The findings suggest the subsurface ocean of Europa may resemble Earth’s oceans. They may also indicate that the ocean floor of Europa is hydrothermally active.