Wall demon on Europa hints at life-favorable brine, study says

Scientists have identified a vast, star-shaped pattern on Jupiter’s icy moon Europa, a feature researchers are calling a wall demon. The pattern, nicknamed Damhán Alla after a Gaelic word for spider or wall demon, spans roughly 1.8 miles (3 kilometers) across and sits inside the 13-mile-wide Manannán crater. Researchers say the formation is not merely a network of surface cracks but a preserved record of salty liquid water that once moved through and beneath Europa’s frozen shell. They believe the pattern formed when a meteor strike melted part of the ice, creating a transient brine-filled network that later refroze, leaving a lasting, lake-star-like imprint on the surface.

The discovery was prompted by a re-examination of images captured by NASA’s Galileo spacecraft in the late 1990s and early 2000s. A US-based team led by physicist Lauren McKeown of the University of Central Florida mapped the crater’s geometry and compared the pattern with similar lake-stars observed in frozen lakes on Earth as well as analogous features found on Mars. The researchers then subjected Europa-like conditions to laboratory tests at NASA’s Jet Propulsion Laboratory to determine whether the same process could produce the giant spider pattern observed on Europa. The team concluded that the dark, branching figure is consistent with a lake-star phenomenon driven by brine migrating from a subsurface reservoir toward the crust.

The pattern’s size and morphology suggest a sub-surface origin tied to Europa’s global ocean, which scientists believe lies beneath a thick icy crust. Europa is widely regarded as one of the prime locations in the solar system to search for life beyond Earth, in part because its ocean could contain more liquid water than all of Earth’s oceans combined when accounting for ice shell thickness and tidal heating. The same tidal forces that drive Europa’s geologic activity also keep the subsurface ocean from freezing, creating a potential habitat where chemical building blocks, energy sources, and liquid water might converge.

The researchers estimate that the brine that formed the feature originated from pockets of salty water beneath the ice, possibly a reservoir as wide as 12 miles (about 19 kilometers) and situated roughly 3.7 miles (about 6 kilometers) below the surface. The team’s simulations reproduced a process in which heat from the initial impact melted a portion of the icy shell, allowing brine to migrate and spread across the surface before freezing into the characteristic spider-like pattern. In field tests at two real-world frozen lakes in Breckenridge, Colorado, the scientists observed lake-star patterns that matched the Europa feature in structure, providing a terrestrial analog for the suspected process.

The existence of brine under Europa’s ice is particularly significant because liquid water is a fundamental criterion for life as we know it. In addition to water, life requires a source of chemical energy and a supply of essential elements such as carbon, hydrogen, and oxygen. Traces of these building blocks have already been detected on Europa’s surface in various minerals and salts, and scientists suspect that hydrothermal activity at the seafloor—analogous to Earth’s deep-sea vents—could provide the energy necessary to support life. The discovery of Damhán Alla reinforces the view that surface features on Europa can reveal processes occurring in the ocean beneath.

The study also underscores Europa’s value as a target for future exploration. NASA’s upcoming Europa Clipper mission is designed to survey the moon’s ice shell and ocean, searching for plumes, brine pockets, and other indicators of habitable conditions. If Damhán Alla-like features prove to be common or widespread, they could help scientists identify regions where surface-terrain features correlate with subsurface activity and potential habitats. The finding adds to the case for including a focus on surface patterns when evaluating candidate sites for detailed observations in the mission’s flybys.

Beyond Europa, Enceladus—the smaller icy moon of Saturn—remains another leading candidate for harboring life due to confirmed plumes containing phosphorus, a key biological element. While Enceladus offers compelling evidence of a chemically rich environment, Europa’s larger ocean and long-standing interest in its habitability keep it at the forefront of life-search discussions in the outer solar system. The Damhán Alla pattern, observed in Europa’s Manannán crater, thus contributes to a broader strategy that combines remote sensing, laboratory analogs, and mission data to assess where life might exist beyond Earth.

The Damhán Alla feature was first identified in Galileo-era images, but the latest analysis reinterprets it through the lens of modern astrobiology and planetary geology. The researchers mapped crater geometry, compared the pattern to Earth lake stars and Martian analogs, and then validated the concept with cold-chamber experiments that simulated Europa-like conditions. The conclusion is that a sub-surface brine pocket, transported by heat-induced melting during the crater-forming event, could produce a surface manifestation similar to a lake-star, offering a non-biological explanation for the pattern while simultaneously signaling past or present exchange between Europa’s ocean and its ice shell. As McKeown noted, such surface features could act as signposts for where to search for life if future missions can sample surface or near-surface materials that connect to the ocean below.

The findings illuminate how Earth analogs can inform the interpretation of extraterrestrial surface geology. They also illustrate the value of revisiting decades-old data with fresh questions and sophisticated modeling. If Europa Clipper confirms the presence of recurrent surface features linked to subsurface brine, scientists could refine their search strategies for biosignatures and identify regions where the exchange between the ocean and the ice shell is most likely to occur. The study does not claim definitive evidence of life, but it does strengthen the case that Europa has conditions compatible with life-supporting processes and that surface features can be indicators of those underlying processes.