NASA scientists have strong evidence that Jupiter’s moon Europa has an internal ocean beneath its icy outer shell – a vast body of salty water swirling around the moon’s rocky interior. New computer modeling suggests that water may actually be pushing the ice shell forward, possibly speeding up and slowing the rotation of the moon’s icy shell over time.

Scientists knew that Europa’s shell is probably “free,” rotating at a different rate than the underlying ocean and rocky interior. The new model is the first to show that Europa’s ocean currents could be contributing to the rotation of its icy shell.

A key element of the study involved calculating drag – the horizontal force exerted by the moon’s ocean on the ice above it. The research hints at how the strength of the ocean current, and its pull against the ice sheet, could even explain some of the geology seen on Europa’s surface. Cracks and ridges could result from the ice shell slowly stretching and collapsing over time as it is pushed and pulled by ocean currents.

For decades, planetary scientists have debated whether Europa’s icy shell might be spinning faster than the deep interior. But instead of linking it to ocean movement, scientists focused on an outside force: Jupiter. They thought that as the gas giant’s gravity pulls on Europa, it also pulls on the moon’s shell and causes it to spin slightly faster.

Europa Clipper, now in the assembly and testing phase, is due to launch in 2024. The spacecraft will begin orbiting Jupiter in 2030 and will use its array of sophisticated instruments to collect scientific data. The mission aims to determine whether Europa, with its deep interior ocean, has conditions that could be suitable for life.

Like a pot of water

Scientists believe that Europa’s internal ocean is heating up from below, due to radioactive decay and tidal heating within the moon’s rocky core. Like water heated in a pot on a stove, Europa’s warm water rises to the top of the ocean.

By including drag in their simulations, the researchers were able to determine that if the currents are fast enough, there could be enough drag on the ice above to speed up or slow down the shell’s spin speed. The amount of internal heating—and therefore, circulation patterns in the ocean—can change over time, possibly speeding up or slowing down the rotation of the ice shell up.

More about shipping

Europa Clipper’s main science goal is to determine if there are places below the surface of Jupiter’s icy moon Europa that could support life. The mission’s three main scientific goals are to understand the nature of the ice shell and the ocean beneath it, along with their composition and geology. The mission’s detailed exploration of Europa will help scientists better understand the astrobiological possibilities for habitable worlds beyond our planet.