The icy white surface of Jupiter's moon Europa is streaked in yellow-brown, cracks made by the ocean below. These dark streaks hint at the chemical composition of the ocean, which is one of the top places to search for alien life. Here's encouraging news: The dark colour may come from sea salt — the same stuff in our oceans.
The new study by NASA scientist comes by way of "Europa in a can", a lab set-up mimicking the surface conditions of Europa. The team took sodium chloride, also known as table salt, and put it inside a -173C vacuum chamber, bombarding it with radiation like that from Jupiter's magnetic field. After several hours — equivalent to a century's worth of radiation from Jupiter — the salt turned brown, the same colour as the cracks on the surface of Europa. The longer the bombardment, the darker the colour.
Previous observations by NASA's Galileo telescope have suggested the colour comes from interactions with sulphur and magnesium on the moon's surface. But this new study adds sodium chloride to the equation. Earth's oceans are dominated by sodium chloride, and the results suggest Europa's ocean could be as well.
We won't know for sure until we visit Europa and get better images of the surface. And you know what, NASA wants to do just that.