NASA scientists have compelling evidence that Jupiter’s moon Europa has an internal ocean beneath its icy outer shell — a vast body of salty water that orbits the moon’s rocky interior. New computer simulations suggest that water may actually be pushing on the icy shell, possibly speeding up and slowing down the rotation of the moon’s icy shell over time.
Scientists know that Europa’s shell is probably free-floating, rotating at a different rate than the underlying ocean and rocky interior. The new simulations are the first to show that Europa’s ocean currents may be contributing to the rotation of its ice sheet.
A key element of the study was the calculation of drag, the horizontal force exerted by the Moon’s ocean on the ice above it. The study hints at how the strength of the ocean current and its drag on the ice sheet may even explain some of the geology seen on Europa’s surface. Cracks and ridges can form as the ice sheet slowly stretches and breaks down over time as it is pushed and pulled by ocean currents.
“Previously, it was known through laboratory experiments and simulations that heating and cooling of Europa’s ocean can cause currents,” said Hamish Hay, a researcher at the University of Oxford and lead author of the study published in JGR: Planets . Hay conducted the research as a research scientist at NASA’s Jet Propulsion Laboratory in Southern California. “Our results now highlight a link between the ocean and ice sheet rotation that has never been considered before.”
Using measurements collected during an upcoming NASA mission Europa Clipper , it is even possible to determine exactly how fast the ice sheet rotates. When scientists compare images collected by the Europa Clipper to those taken by past NASA missions Galileo and Voyager they will be able to study the location of ice surface features and potentially determine whether the position of the moon’s ice sheet has changed over time.
For decades, planetary scientists have debated whether Europa’s icy shell could be spinning faster than its deep interior. But instead of linking it to ocean movement, scientists focused on an outside force: Jupiter. They hypothesized that as the gas giant’s gravity tugs on Europa, it also tugs on the moon’s mantle and causes it to spin a little faster.
“It was completely unexpected to me that what was happening in the ocean circulation could be enough to affect the ice sheet. It was a huge surprise,” said co-author and Europa Clipper project scientist Robert Pappalardo of JPL. “The idea that the cracks and ridges we see on Europa’s surface might be related to the circulation of the ocean below—geologists don’t usually think, ‘Maybe the ocean is doing this.’
The Europa Clipper, currently under construction, testing and launch at JPL, is scheduled to launch in 2024. The spacecraft will begin orbiting Jupiter in 2030 and will use a suite of sophisticated instruments to gather scientific data as it flies past him . about 50 times a month. The mission aims to determine whether Europa, with its deep interior ocean, has conditions suitable for life.
Like a pot of water
Using methods developed to study the Earth’s ocean, the authors of the article relied on NASA supercomputers , to create large-scale models of Europa’s ocean. They explored the intricacies of how water circulates and how heating and cooling affect this movement.
Scientists believe that Europa’s inner ocean is being heated from below by radioactive decay and tidal heating in the moon’s rocky core. Like water heating in a pan on a stove, Europe’s warm water rises to the top of the ocean.
In the simulations, the circulation initially moved vertically, but the rotation of the Moon as a whole caused the flowing water to be deflected in a more horizontal direction – in east-west and west-east currents. By accounting for drag in their simulations, the researchers were able to determine that if the currents were fast enough, there could be enough drag on the ice above to speed up or slow down the shell’s rotation rate. The level of internal heating – and thus the circulation patterns in the ocean – can change over time, potentially speeding up or slowing down the rotation of the overlying ice sheet.
“This work could be important for understanding how the rotation rates of other ocean worlds may have changed over time,” Hay said. “And now that we know about the potential connection of the interior oceans to the surface of these bodies, we can learn more about their geological history, as well as the history of Europa.”
More about the mission
Europa Clipper’s main science goal is to determine if there are places beneath 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 shell and the ocean beneath it, as well as their composition and geology. A detailed study of Europa during the mission will help scientists better understand the astrobiological potential of inhabited worlds beyond our planet.
Led by the Cal Institute of Technology in Pasadena, California, JPL is leading the 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 developed the spacecraft’s main body 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 manages the Europa Clipper mission program.