Europa is the softest, solid object in our solar system, thanks to its thick, icy envelope. Yet beneath its smooth exterior, Jupiter’s fourth-largest moon appears to hold secrets, a deep, salty ocean with intriguing potential for extraterrestrial life.
This ocean makes Europa a prime target for scientific studies, including two separate orbital missions scheduled to be launched to Jupiter within the next two years.
And while it will take several years for either probe to arrive, scientists are already shedding light on Europa in other ways, gleaning information from telescope observations, past flybys of the probes, lab experiments, and computer simulations.
in a new studyResearchers from the Jet Propulsion Laboratory (JPL) at Caltech in the US and Hokkaido University in Japan used NASA supercomputers to examine a lesser-known anomaly from Europa: why does the icy crust spin faster than the interior?
According to their research, the asynchronous rotation of the surface could be caused by ocean currents pushing from below. It’s surprising, says lead author and JPL researcher Hamish Hay, now at the University of Oxford. It’s a revelation that could provide new clues to what’s going on there.
“Prior to this, it was known from laboratory and modeling experiments that the heating and cooling of the European ocean can lead to currents,” Hay said. He said. “Now our results highlight a coupling between ocean and ice crust circulation that had not been considered before.”
The ice shell floats on Europa’s ocean, so it can rotate independently of the rest of the oceans the moon, including oceanic, rocky and mineral interiors. Scientists suspected this for a long time, but the forces behind the projectile’s spin are a mystery.
Europa is subject to tidal bending by Jupiter, which is deformed the moon thanks to its strong attractiveness. This massive tug of war caused cracks in Europa’s ice crust and likely generated some heat from the mantle and core.
With thermal energy released by the radioactive decay, this heat from Europe’s interior is thought to rise across the ocean to the frozen surface like a water-heating pot on a stove.
Combined with Europa’s rotation and other factors, this vertical temperature gradient must fuel fairly strong ocean currents.
And, the study estimates, these currents could be strong enough to move the global ice sheet above our heads. No one knows exactly how thick the crust is, but estimates vary from about 15-25 kilometers (15 miles) thick.
While scientists knew that Europa’s ice crust might have been spinning on its own, they focused on the influence of Jupiter’s gravity as the driving force.
He added, “For me, it was completely unexpected that what was happening in the ocean circulation would be enough to influence the ice crust. It was a big surprise.” He said Study co-author and Europa Clipper project scientist Robert Pappalardo of NASA’s Jet Propulsion Laboratory.
He added: “The idea that the cracks and ridges we see on Europa’s surface might be related to the ocean cycle below — geologists don’t usually think, ‘Maybe this is the ocean doing it.'” Add.
The researchers used NASA supercomputers to build complex simulations of Europa’s ocean, borrowing techniques that have been used to model oceans on Earth.
These models allow them to dig into the details of water circulation over Europa, including how these patterns are affected by ocean warming and cooling.
The main focus of the study was drag, or the horizontal force of the ocean that pushes the ice above it. By analyzing the drag in their simulations, the researchers found that certain fast-moving currents can produce enough drag to speed up or slow down the rotation of Europa’s ice cap.
Although this effect depends on the speed of the currents, the researchers note that the internal heating of Europa can change over time. This can lead to a corresponding change in the speed of ocean currents, which in turn causes the ice crust to rotate faster or slower.
In addition to helping us understand Europa, this research may also apply to other ocean worlds, the researchers note, where surface features could offer clues to hidden waters below.
“Now that we know the possible coupling of the inner oceans with the surfaces of these bodies, we can learn more about their geological history as well as the history of Europe,” Hay said. He said.
Those Explorer of the icy moons of Jupiter Scheduled to launch in April 2023, JUICE will begin its journey to study the three large ocean moons of Jupiter: Ganymede, Callisto and Europa.
At the end of 2024, NASA plans to launch a rocket Clipper Europe orbiter, which will perform approximately 50 close flybys to study the potential habitability of the moon. According to the authors of the new study, it may even be able to accurately measure the rotational speed of Europa’s ice cap.
The study has been published in JGR Planets.