Europa is a prime candidate for the search for extraterrestrial life in the solar system, due to the supposed presence of an ocean of liquid water.

But the latter would be located under a thick layer of ice, up to 20 to 30 kilometers below the surface, according to data collected by space probes.

However, part of this water could be much closer to the surface than imagined, according to the study published Tuesday in Nature communications, which underlines that Europa is "young and geologically active".

The most common structure there consists of double ridges, a kind of furrow that can stretch for hundreds of kilometers and whose edges can rise up to several hundred meters.

Scientists have put forward several hypotheses to explain their formation, and in particular an interaction between the inner ocean and the layer of ice that covers it.

But the difficulty for water to pass through such a thick surface has led to speculation that the formation of the ridges takes place with pockets of water located just below the surface.

This is precisely what a team of geophysicists from the American University of Stanford was able to observe... in Greenland, an island mainly covered in ice.

They discovered "a double ridge of ice that has a shape similar to those of the double ridges found on Europa", explained to AFP Riley Culberg, doctoral student in electrical engineering at Stanford and main author of the study.

It is about 800 meters long with an average height of 2.1 meters, and is located about 60 km from the coast in northwest Greenland.

From one to five km deep

His colleague Dustin Schroeder, professor of geophysics at Stanford, explains that they were "working on something completely different in relation to climate change and its impact on the surface of Greenland, when we saw these small double- ridges".

Satellite images and data collected by airborne radar made it possible "for the first time to see something similar (to Europa) on Earth and to observe the processes below the surface that led to the formation of the ridges", said explained Riley Culberg.

The team modeled a process involving the freezing, pressurization and fracture of a shallow water pocket, leading to the formation of the double ridge.

“The water we observed in Greenland is in the top thirty meters of the ice sheet,” says Culberg.

On Europa, whose ridges are much higher and longer, he estimates that "pockets of water could form between one and five kilometers deep".

If their mechanism of formation is indeed the one proposed, these pockets could be very widespread.

And if the water that composes them comes from the internal ocean, they could contain traces of extraterrestrial life.

Two future space missions will provide more information, from 2030. Europa Clipper, for NASA, will be equipped with a radar similar to that used to study Greenland.

JUICE, for the European Space Agency (ESA), will also look at Europa as well as Jupiter's two other icy moons, Io and Ganymede.

© 2022 AFP