If alien life exists within our solar system, Jupiter’s moon Europa is among the most promising places to search for it. This fascinating world contains a massive saltwater ocean hidden under 10 to 20 miles of ice, which has long distinguished it as a potentially hospitable habitat for extraterrestrial organisms—though accessing such a deep environment would prove challenging for any life-seeking missions.
But now, scientists have presented exciting new evidence for the existence of shallow pools of water that may lie much closer to the moon’s surface, perhaps even less than one mile under the ice. This prospect would both boost the odds that life exists on Europa and make any speculative aliens there much simpler for future missions to find.
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Researchers led by Riley Culberg, a PhD student in electrical engineering at Stanford University, concluded that “shallow water processes may be even more dominant in shaping Europa’s dynamics, surface morphology, and habitability than previously thought,” according to a study published on Tuesday in Nature Communications. The new discovery, based on observations of Europa-like ridges in Greenland, came about by sheer chance.
“It was really a bit of serendipity,” Culberg said in an email. “One of my colleagues on the paper, who is a planetary scientist, was giving a presentation to our research group on the big open questions in Europa science and showed a picture of these double ridges on the surface. It struck me that I had seen a very similar looking feature in my own data from Earth while working on a totally different project related to climate change impacts on the Greenland Ice Sheet.”
“It turns out that double ridges on Europa have a very characteristic ratio between the height of the ridges and the distance between the two peaks, and after accounting for the difference in gravity between Earth and Europa, we found that this Greenland feature has a pretty similar relationship,” he added.
These icy features are bordered by two quasi-symmetric ridge pairs, separated by a central valley, according to the study. The ridges are etched all across Europa, but they are rare on our own planet. Only within the past decade have the structures been observed in any detail, by two NASA missions: the ICESat-2 satellite and the airborne Operation IceBridge project.
ICESat-2 captured the formation of double ridges in Northwestern Greenland beginning in 2013, while subsequent IceBridge observations revealed that there are pools of shallow water, called sills, underneath them.
Subsequent studies have suggested that the double ridges are the result of a cycle in which liquid water freezes and thaws in the high-pressure environments inside the ice sheet, causing it to thrust upward over and over, hammering out the idiosyncratic two-peaked structure. If similar processes are responsible for the same double ridges on Europa, it could hint at the presence of shallow water aquifers anywhere from under a mile to a few miles beneath the moon’s surface.
“One of the big questions that remains from our study is exactly how this mechanism would scale to Europa, where the temperature, pressure, and chemistry are so different from Greenland,” Culberg explained. “So there’s a lot of work we could do in collaboration with scientists who work on numerical models of ice behavior to understand things like exactly how deep or large these water pockets would be or how long they would take to refreeze.”
“It would also be great to get on-the-ground measurements from this ridge system in Greenland to better understand its evolution and the precise conditions in the sill,” he added.
Such a habitat on Europa would likely still be shielded from the harsh radiation, emitted by Jupiter, that batters the moon’s surface. Moreover, it would also provide important evidence that water is moving from the ocean to the surface via the ice shell, which boosts the odds that this world is habitable—though it is not a slam dunk case for alien life.
“The presence of liquid water in the ice shell would suggest that exchange between the ocean and ice shell is common, which could be important for chemical cycling between the surface and ocean that would help support life,” Culberg said. “Shallow water in particular also means that there might be easier targets for future space missions to image or sample that could at least preserve evidence of life, without having to fully access the deep ocean.”
“Whether or not these shallow water pockets could be habitable environments themselves would depend on a lot of questions of the pressure and chemistry in the water pocket and how long it lasts, which we don’t yet know,” he noted.
Some of these open questions could be resolved by future voyages to study this alluring ice moon up close. NASA plans to launch a mission called Europa Clipper in the coming years, which will reach Jupiter around 2030. The mission is tasked with assessing its habitability during a number of close flybys, and is hopefully the first of many dedicated trips to the moon.
Perhaps some day decades from now, a lander will be able to confirm the existence of these shallow sills on Europa, and any organisms that might be thriving inside them. Such a discovery would shake the foundations of science and society, and would serve as a reminder that our search for life elsewhere in the universe is often inspired by the earthly structures right here at home.
