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NASA scientists have strong evidence that Jupiter’s moon Europa has an internal ocean beneath its outer ice shell: this ocean is a huge body of salty water that churns around the moon’s rocky interior. A new computer model suggests that water could be pushing on the ice shell, possibly speeding up and slowing down the rotation of this moon’s ice crust over time.
Scientists have learned that Europa’s crust is likely buoyant and rotates at a different rate than the ocean below and its rocky interior. The new model is the first to show that Europa’s ocean currents could be contributing to the rotation of its ice sheet.
A key element of the study was to calculate drag: the horizontal force that this moon’s ocean exerts on the ice above it. The research hints at how the power of ocean flow and its resistance against the ice sheet might even explain some of the geology seen on Europa’s surface. The cracks and ridges could be the result of the ice sheet slowly stretching and collapsing over time as ocean currents push and pull on it.
“Prior to this, it was known through modeling and laboratory experiments that warming and cooling of Europa’s ocean could drive currents,” said Hamish Hay, a researcher at the University of Oxford and lead author of the study published in JGR: Planets. Hay conducted this study while he was a postdoctoral research associate at NASA’s Jet Propulsion Laboratory (JPL) in Southern California. “Now, our results highlight a coupling between the ocean and ice sheet rotation that has never been considered before.”
It might even be possible, using measurements collected by NASA’s upcoming Europa Clipper mission, to determine precisely how fast the ice sheet is rotating. When scientists compare images collected by Europa Clipper with those captured in the past by NASA’s Galileo and Voyager missions, they will be able to examine the location of ice surface features and potentially determine whether the position of the ice sheet on the moon has changed over time.
For decades, planetary scientists have debated whether Europa’s ice sheet might be rotating faster than its deep interior. But instead of linking this to the movement of the ocean, scientists focused on an external force: Jupiter. They hypothesized that as the gas giant planet’s gravity pulls on Europa, it also pulls on the moon’s crust, causing it to spin a bit faster.
“For me, it was completely unexpected that what happens in the ocean circulation could be enough to affect the ice sheet. That was a big surprise,” said JPL’s Robert Pappalardo, who is a co-author and a Europa Clipper project scientist. “And the idea that the cracks and ridges we see on Europa’s surface could be linked to the circulation of the ocean below… Geologists don’t often think, ‘Maybe the ocean is doing that.'”
Europa Clipper—currently in its assembly, testing, and launch operations stage at JPL—is scheduled for launch in 2024. The spacecraft will begin orbiting Jupiter in 2030 and will use its suite of sophisticated instruments to collect scientific data as it flies by the moon. about 50 times. The mission aims to determine if Europa, with its deep internal ocean, has conditions that could be suitable for life.
like a pot of water
Using techniques developed to study Earth’s ocean, the paper’s authors relied on NASA supercomputers to make large-scale models of Europa’s ocean. They explored the intricacies of how water circulates and how heating and cooling affect that movement.
Scientists think Europa’s internal ocean is warming from below, due to radioactive decay and tidal heating within the moon’s rocky core. Just like water being heated in a pot on a stove, Europa’s warm water rises to the surface of the ocean.
In the simulations, the circulation initially moved vertically, but the moon’s rotation as a whole caused the water to flow in a more horizontal direction, in east-west and west-east currents. The researchers, by including drag in their simulations, were able to determine that if the currents are fast enough, there could be adequate drag in the ice above to speed up or slow down the rate of crustal rotation. The amount of inland warming, and therefore the circulation patterns of the ocean, could change over time, speeding up or slowing down the rotation of the ice sheet above.
“This work could be important in understanding how the rotation rates of other ocean worlds may have changed over time,” Hay said. “And now that we know about the possible coupling of the interior oceans with the surfaces of these bodies, we may learn more about their geological histories and that of Europa.”
More about the mission
Europa Clipper’s main scientific goal is to determine whether there are places below the surface of Jupiter’s icy moon Europa that could harbor life. The mission’s three main science goals are to understand the nature of the ice sheet and the ocean beneath it, along with its composition and geology. The detailed exploration of Europa carried out by this mission will help scientists to better understand the astrobiological potential of habitable worlds beyond our planet.
Managed by Caltech in Pasadena, California, JPL is leading development of the Europa Clipper mission in partnership with the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, for NASA’s Science Mission Directorate in Washington. APL designed the main body of the spacecraft in collaboration with JPL and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The Planetary Missions Program Office at NASA’s Marshall Space Flight Center in Huntsville, Alabama, runs program management for the Europa Clipper mission.
For more information on Europe, visit: europa.nasa.gov