NASA's Europa flyby suggests “something” moving under the ice

Landmarks on Europa's surface indicate that the icy crust is at the mercy of the waters below. More importantly, Juno's recent visit revealed what may be plume activity, which if real would allow future missions to sample the inner ocean without having to land.

It has been nearly two years since Juno made its closest approach to Europa, but its observations are still being analysed. Remarkably, despite having been orbiting Jupiter since 2016, five images taken by Juno on September 29, 2022, were the first close-ups of Europa since the last visit by the Galileo spacecraft in 2000.

This arguably represents a shocking neglect of one of the solar system's most interesting worlds, but it may also have provided a long baseline for figuring out what's changed.

Europa is the smoothest body in the solar system, thanks to the constant reemergence driven by its inner ocean. However, it is far from featureless, and Juno has observed some steep depressions 20 to 50 km (12 to 31 mi) wide and fracture patterns that are thought to indicate “Real polar walkthrough“.

“True polar wandering would occur if Europa's icy crust separated from its rocky interior, resulting in high stress levels on the crust, leading to predictable fracture patterns,” Dr. Candy Hansen of the Planetary Science Institute said in a study. statement.

The idea behind true polar wandering is that the crust that lies above Europa's inner ocean rotates at a different rate than the rest of the moon. It is believed that the water below is moving, pulling the shell with it, as currents within the ocean affect the shell's movements. These currents, in turn, are presumably driven by heating within Europa's rocky core, where the gravitational pull of Jupiter and its larger moons turns Europa into a giant pressure ball.

In the process, interactions between the ocean and ice can stretch and compress areas, creating the cracks and ridges seen since Voyager 2's visit.

Hansen is part of a team exploring Juno images of Europe's southern hemisphere. “This is the first time such rifting patterns have been mapped in the Southern Hemisphere, suggesting that the impact of true polar wandering on Europa's surface geology is more extensive than previously identified,” the scientist said.

Not all changes to the maps of Europe are the result of internal ocean currents. NASA seems to be falling into the trap of optical illusions. “Crater Gwern no longer exists,” Hansen said. “What was previously thought to be a 13-mile-wide impact crater – one of the few documented impact craters in Europe – Gwern, was revealed in JunoCam data as a set of intersecting ridges that created an oval shadow.”

However, Juno gives more than he takes. The team is excited about something they call the platypus because of its shape, not because it has a bunch of features that shouldn't go together. The ridge formations at its edge appear to be collapsing, and the team believes this process could be caused by pockets of salt water that have partially penetrated the ice crust.

Such pockets would be interesting, indirect targets for study by the Europa Clipper, but more interesting are the dark patches that may have been deposited by cryovolcanic activity.

“These features indicate current surface activity and the presence of liquid water beneath Europa's surface,” said Heidi Becker of the Jet Propulsion Laboratory. Such activity has been confirmed at Enceladus hot springs, but there is conflicting evidence about whether it is currently occurring in Europa.

Such activity would make it possible to sample the inner ocean for signs of life by simply flying through a plume and collecting some ice flakes, without having to land, let alone dig.

Currently, polar wandering may cause very modest adjustments to the locations of features on Europa's surface, but there is evidence of a shift millions of years ago of more than 70 degrees, for unknown reasons.