Europa is the most solid object in our Sun, thanks to its ice shell. But behind its smooth exterior, Jupiter’s fourth-largest moon appears to hold a secret – a deep, salty ocean that could harbor alien life.
That ocean makes Europa a prime target for scientific research, including two separate orbiters that will launch to Jupiter in the next two years.
And while it will be several years before any other probes arrive, scientists are already illuminating Europa in other ways, getting information from telescope observations, past broadcasts, lab experiments, and computer simulations.
In a new study, researchers from the Jet Propulsion Laboratory (JPL) at the California Institute of Technology in the US and Hokkaido University in Japan used NASA’s supercomputers to investigate a mystery about Europa: Why does the shell rotate faster than the interior?
According to their research, atmospheric fluctuations can be caused by ocean currents pushing up from the ground. That’s a big revelation, explains lead author and JPL researcher Hamish Hay, who is now at the University of Oxford; it’s a revelation that can provide new insights into what’s going on down there.
“Prior to this, it was known through laboratory experiments and demonstrations that the heating and cooling of Europa’s oceans can drive currents,” says Hay. “Now our results show a connection between the ocean and the shell’s circulation that was not thought of before.”
The shell floats on Europa’s ocean, so it can be rotated infinitely month, including oceans, rock interiors, and metal foundations. Scientists have long suspected this, but the force driving the bullet is amazing.
Europa is modified by Jupiter’s currents, which disturb it month through strong gravity. This powerful drag causes cracks in Europa’s ice sheets and probably warms the mantle.
Along with the thermal energy released from radioactive decay, this heat from Europa’s interior is thought to rise from the ocean to the icy surface like a pot of water on a stove.
Coupled with Europa’s variability and other factors, this vertical heating should promote very strong ocean currents.
And according to the study’s estimates, those waves could be strong enough to move ice around the world. No one knows how thick the shell is, but estimates range from 15 to 25 kilometers (15 miles).
Although scientists knew that Europa’s icy shell rotated on its own, they focused on Jupiter’s gravity as the driving force.
“To me, it was completely unexpected that what happens in the oceans would be enough to affect the ice shell. This was very surprising,” said study co-author and Europa Clipper Project scientist Robert Pappalardo, of NASA’s Jet Propulsion Lab.
“And the idea that the cracks and ridges that we see on the surface of Europa could be connected to the movement of seas on the ground – geologists don’t think, ‘Maybe it’s the sea that’s doing it,'” he adds.
The researchers used NASA’s supercomputers to create complex maps of Europa’s oceans, borrowing techniques that have been used to measure Earth’s oceans.
These models allow them to study in depth the water cycle in Europa, including how these processes are affected by the warming and cooling of the oceans.
The main focus of the study was drag, or the horizontal force of the ocean pushing the ice on top of it. Based on their experiments, the researchers found that certain tidal waves can produce enough energy to speed up or slow down the ice cycle on Europa.
Although this depends on the speed of the tides, the researchers note that the temperature of Europa’s interior can vary over time. This can cause the sea level to fluctuate more and more, which in turn causes the glaciers to fluctuate faster or slower.
Beyond helping us understand Europa, the research could also apply to other ocean worlds, the researchers suggest, where surface images can provide clues about the hidden waters below.
“And now that we know about the possible connections between the oceans and the environment of these bodies, we can learn more about their history and about Europa,” says Hay.
ESA’s Jupiter Icy Moons Explorer (JUICE) is expected to launch in April 2023, beginning its journey to study Jupiter’s three largest, oceanic moons: Ganymede, Callisto, and Europa.
In late 2024, NASA plans to launch its Europa Clipper mission, which will make about 50 missions to explore the moon’s atmosphere. According to the authors of the study, it could even accurately measure how fast Europa’s ice shell is rotating.
This study was published in JGR Planets.
