On the white, cracked surface of Europa, Jupiter's icy moon, there's a mark that looks like something out of Stranger Things: a branching structure, with arms extending like frozen tentacles across the ice.

For years it was little more than a curiosity captured by NASA's Galileo spacecraft in the late 1990s, an anomaly without a clear explanation on one of the solar system's most intriguing worlds.

Today, however, that scar has a name—Damhan Alla, "spider" or, more evocatively, "wall demon" in Irish—and has sparked renewed interest in planetary research.

Located within the Manannan crater, the structure could offer key clues about what lies beneath Europa's thick icy crust and, especially if similar formations are identified in the future, about the possibility of life beyond Earth.

Renewed attention comes thanks to a study published in The Planetary Science Journal and led by physicist Lauren McKeown, a professor at the University of Central Florida and a student at Trinity College Dublin, along with researchers from NASA's Jet Propulsion Laboratory (JPL), Brown University, and the Planetary Science Institute.

The new work proposes that Damhan Alla formed after an impact fractured the surface ice, allowing salty water from the subsurface to briefly emerge before refreezing, leaving its distinctive shape imprinted.

Lake stars: Europa's terrestrial analogue

To decipher the origin of this peculiar formation on Europa, the team first looked for an analogue on Earth. He found it in so-called "lake stars": radial patterns that appear when snow covers a frozen lake and liquid water manages to break through to the surface, melting the snow and forming branch-like structures. On our planet, these stars are only a few meters in diameter; on Europa, however, Damhan Alla extends for approximately one kilometer.

With this parallel as a starting point, researchers conducted field tests on two frozen lakes in Colorado—Ollie's Pond and Maggie Pond—where they identified multiple analogous formations.

These observations were complemented by laboratory experiments, in which they recreated the process using ice simulators and temperature-controlled chambers.

In parallel, the team developed computer models and analyzed in detail the images captured by the Galileo probe, with the aim of understanding the geometry and formation mechanism of Damhan Alla on Jupiter's moon.

NASA's Galileo probe detected a strange spider-like formation inside the Manannan crater on Europa's icy surface. Image: NASA/JPL/University of Arizona

A discovery with an Irish name

The name Damhan Alla is no coincidence. The study was led by Professor McKeown, a native of Churchtown, Dublin, Ireland, along with a team that included other Irish scientists, among them Dr. Jennifer Scully, also a graduate of Trinity College Dublin. “Since Jen and I are Irish, and given that many geographical features in Europe already have Irish and Celtic names—including the Manannan crater, referring to the 'son of the sea' in Irish mythology—we decided to name it after the Irish word for spider,” McKeown explained in a Trinity College press release. The name also serves a practical purpose: to distinguish this structure from the so-called “Martian spiders,” visually similar formations but caused by completely different processes. As DW previously reported, on the Red Planet, these arise from gas flows associated with the sublimation of carbon dioxide (CO?), a mechanism unrelated to saltwater, which, according to the new study, would have shaped Damhan Alla.

Europa: Subsurface Ocean and the Possibility of Extraterrestrial Life

Europa has long been one of the most promising candidates for harboring extraterrestrial life in the solar system. Beneath its icy crust, scientists suspect the existence of a global ocean of saltwater, and formations like Damhan Alla could be signs that this ocean is not completely isolated, but rather occasionally interacts with the surface.

In fact, Europa has some of the most unique surface features in the entire solar system. Unlike other rocky bodies riddled with impact craters, Europa is almost entirely devoid of them. For now, the study of Europa still relies heavily on images taken by the Galileo probe more than two decades ago. But that could change with NASA's Europa Clipper mission, scheduled to enter orbit around Jupiter in 2030. The spacecraft will search for signs of liquid water beneath the ice and map Europa's surface with unprecedented resolution.

According to Universe Today, Europa Clipper is expected to cover up to 95% of the moon's surface, compared to the meager 10–14% available so far.

If, in this process, he manages to identify more "spider-like" structures like Damhan Alla, it would strengthen the hypothesis of activity beneath the icy layer and, perhaps, of conditions favorable for life. Meanwhile, McKeown is continuing this line of research in a new laboratory called FROSTIE, where he will develop low-pressure experiments designed to simulate environments like those on Europe. The goal is to test whether these structures can form naturally under a frozen crust, analogous to how lava moves beneath Earth's surface. Although some questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that, beneath its icy surface, a world far more active than it appears could be hidden. where it will conduct low-pressure experiments designed to simulate environments like those on Europa. The goal is to test whether these structures can form naturally under a frozen crust, analogous to how lava moves beneath Earth's surface. Although questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that a world far more active than it appears could be hidden beneath its icy surface. Where it will conduct low-pressure experiments designed to simulate environments like those on Europa. The goal is to test whether these structures can form naturally under a frozen crust, analogous to how lava moves beneath Earth's surface. Although questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that a world far more active than it appears could be hidden beneath its icy surface.Although some questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that, beneath its icy surface, a world far more active than it appears could be hidden. where it will conduct low-pressure experiments designed to simulate environments like those on Europa. The goal is to test whether these structures can form naturally under a frozen crust, analogous to how lava moves beneath Earth's surface. Although questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that a world far more active than it appears could be hidden beneath its icy surface. Where it will conduct low-pressure experiments designed to simulate environments like those on Europa. The goal is to test whether these structures can form naturally under a frozen crust, analogous to how lava moves beneath Earth's surface. Although questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that a world far more active than it appears could be hidden beneath its icy surface.Although some questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that, beneath its icy surface, a world far more active than it appears could be hidden. where it will conduct low-pressure experiments designed to simulate environments like those on Europa. The goal is to test whether these structures can form naturally under a frozen crust, analogous to how lava moves beneath Earth's surface. Although questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that a world far more active than it appears could be hidden beneath its icy surface. Where it will conduct low-pressure experiments designed to simulate environments like those on Europa. The goal is to test whether these structures can form naturally under a frozen crust, analogous to how lava moves beneath Earth's surface. Although questions remain—such as whether Damhan Alla is a rarity or just one among many similar structures hidden beneath the ice—the study opens up new hypotheses about Europa's internal dynamics and reinforces the idea that a world far more active than it appears could be hidden beneath its icy surface.