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The ocean underneath Europa’s icy shell may have a jet stream around its equator, which could be making the surface crack and stirring around compounds important for life.

Jupiter’s powerful magnetic field extends out nearly 5 million kilometres on average, enveloping the planet’s major moons. One of these moons, Europa, has a salty liquid ocean beneath the ice. This salt would make the ocean conduct electricity, which means that a rotating magnetic field could apply a force to it and make the water move.

Christophe Gissinger at the École Normale Supérieure and Ludovic Petitdemange at the Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres, both in Paris, used measurements from the Galileo spacecraft to calculate how Jupiter’s magnetic field could move Europa’s ocean.

They found that it would probably cause a jet stream around the equator moving a few centimetres per second in the opposite direction of Europa’s spin. This stream flowing against the moon’s rotation could stress the surface, causing it to crack around the equator.

“It will not slow down the entire moon because the tidal forces from Jupiter are huge and will keep Europa’s rotation the same, but it will create these cracks that we have seen,” says Gissinger.

Some of the energy from the magnetic field could also dissipate as heat, which would then flow towards the poles, thinning the ice shell and possibly creating the conditions necessary for the plumes of water we’ve seen spurting out of Europa.

The stream may be similar to Earth’s Gulf Stream, a vast current in the Atlantic Ocean, Gissinger says. If Europa’s ocean has life, the ocean’s flow could be key to nourishing and spreading it. “We know on Earth that the Gulf Stream is very important for transporting compounds which are important for life,” he says.