Earthly comparison hints at shallow liquid water on Jupiter’s moon

Researchers have revealed new insight into the geology of Jupiter’s moon Europa, described by NASA as one of the most promising locations in our solar system for present-day extraterrestrial life.

Scientists strongly suspect that Europa, one of an estimated 79 moons orbiting the planet Jupiter, harbours liquid water in the form of a large saltwater ocean beneath a frozen icy crust. Europa’s ice “shell” is estimated to be 20-30 kilometres thick.

In a paper published today in Nature Communications, a research team led by Riley Culberg of Stanford University, US, presents evidence that shallow liquid water also exists much closer to Europa’s surface, within the ice shell.

Europa’s ice shell is covered in landforms called “double ridges” – consisting of two ridges of ice that are nearly symmetrical on either side of a shallow trough – up to hundreds of kilometres long.

In the new study, the researchers investigated a double ridge found on Earth in the ice sheet over northwest Greenland. The double ridge is very similar in shape to those found on Europa.  

Using surface elevation and radar sounding data, the team found that the Greenland double ridge was probably formed by shallow liquid water within the ice sheet gradually refreezing, becoming pressurised and eventually fracturing the ice.

This finding implies that a similar mechanism might cause the double ridges on Europa as well – although there are some differences. In Greenland, the regions of shallow liquid water are formed by drainage of meltwater from the surface. On Europa, the liquid water might instead be injected from below, originating from the moon’s subsurface ocean.

The study suggests that shallow liquid water may be more important to shaping Europa’s surface than previously recognised.

“If this mechanism controls double ridge formation at Europa, the ubiquity of double ridges on the surface implies that liquid water is and has been a pervasive feature within the brittle lid of the ice shell,” Culberg and colleagues write.  

With NASA’s Europa Clipper mission scheduled to be launched in October 2024, we’ll no doubt learn much more in the coming decades about the geology of this intriguing moon – and its potential to harbour life.