Science

We now know how the mysterious ridges covering Europa’s surface formed

Jupiter’s moon Europa is covered in weird pairs of ridges, and they may come from the refreezing of shallow pockets of liquid water hiding all over its icy shell



Space



19 April 2022

Europa, one of Jupiter’s moons, has a surface criss-crossed by multiple sets of ridges

NASA/JPL/ASU

Jupiter’s moon Europa is covered in strange pairs of parallel ridges. Now, researchers have found a similar feature in Greenland and used it to unravel how such ridges form – which may help us understand how Europa’s subsurface ocean interacts with its icy shell.

Europa has parallel pairs of ridges hundreds of kilometres long and hundreds of metres high all across its surface, but it has been difficult for researchers to explain how they came about because we have no direct data on what is going on under the surface.

“It’s a bit of a mystery to us at the moment what the structure of the ice shell is,” says Riley Culberg at Stanford University in California. “These double ridges are the most common surface feature that we see, so they have potential to be a particularly good way to understand the ice shell more generally.”

Culberg spotted a similar pair of ridges in satellite images of the Greenland ice sheet. He and his colleagues analysed how these formed and found that it was due to pockets of liquid water within the ice sheet. When some of that water refreezes, it expands, creating cracks in the ground and pressurising the remaining water, which pushes upwards on either side of the refrozen section. That upwelling causes the parallel ridges.

If the same process creates the ridges across Europa, that implies that there is shallow water within its 20 to 30-kilometre-thick shell of ice – something that has been suggested before, but never in connection with the ridges. “Double ridges are so common across the surface, you really have to have this shallow water pretty much everywhere,” says Culberg.

This might be good for the prospect of life on Europa. “If there’s a lot of shallow water in the ice shell, it means that there has to be some amount of exchange between the ocean and the surface,” says Culberg. “That kind of movement allows for the mixing of chemistry and heat that you need in order for life to happen.” If there is life in Europa’s ocean, it might also make its way into these pockets of fluid, making it far easier to find, he says.

Journal reference: Nature Communications, DOI: 10.1038/s41467-022-29458-3

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