Jupiter's icy moon Europa is an ocean world that is a prime candidate in the search for potential extraterrestrial habitability and life beyond Earth. Europa's surface contains many features that are thought to originate from brine sources within its icy shell, which may represent the most accessible bodies of liquid water in our solar system. An intriguing possible example is the star-shaped “spider” in the center of Manannan Crater, discovered by NASA's Galileo mission. Planetary scientists now present a new hypothesis for the formation of this arachnid object, based on morphological analysis and preliminary analogue modeling. They suggest that this feature may arise from a process similar to the formation of dendritic “lake stars” – seasonal features found in frozen ponds and lakes on Earth.
Geomorphological map of Damkhan Alla Manannan. Image credit: Mac Keown etc.., two: 10.3847/PSJ/ae18a0.
“This spider-like feature could have been formed by the eruption of molten brines following the Manannan impact,” said Dr. Elodie Lesage, a researcher at the Planetary Science Institute.
“This will mean it can inform us about the properties of the subsurface and the composition of the brine at the time of impact.”
Dr Lesage and his colleagues are also studying Martian “spiders” – branching tree-like structures that form in the regolith near Mars' south pole.
They applied this knowledge to the surfaces of other planets, including Jupiter's icy moon Europa.
While Martian spiders form when dust and sand are disrupted by escaping gas under a seasonal layer of dry ice, the team's work on Europa argues that the star-shaped feature may have formed after an impact.
“Lake stars on Earth are radial, branching patterns that form when snow falls on frozen lakes, and the weight of the snow creates holes in the ice, allowing water to flow through the snow, melting it and spreading out in an energetically favorable manner,” said Dr. Lauren McKeown, a researcher at the University of Central Florida and NASA's Jet Propulsion Laboratory.
“We think Europa could have erupted an underground reservoir of salt water after the impact and spread through the porous surface ice, creating a similar pattern.”
Researchers have informally named Europa's feature Damhan Alla, which means “spider” in Irish, to distinguish it from Martian arachnids.
To test their formation hypothesis, they also conducted field and laboratory experiments, observing lake stars in Breckenridge, Colorado, and recreating the process in a cryogenic glovebox using Europa ice models cooled by liquid nitrogen.
“We ran water through these simulators at different temperatures and found that similar star-shaped patterns formed even at extremely low temperatures (minus 100 degrees Celsius or minus 148 degrees Fahrenheit), supporting the idea that the same mechanism could occur on Europa after an impact,” said Dr. Mac Keown.
Scientists modeled how brine beneath Europa's surface might behave after this impact, and the team created an animation to illustrate the process.
Observations of Europa's icy structure have been limited to images from the Galileo spacecraft since 1998, but the authors hope to resolve the issue with higher-resolution images from the Europa Clipper mission, a NASA spacecraft due to arrive in the Jupiter system in April 2030.
“Although the lake stars provided valuable information, conditions on Earth are very different from those in Europe,” Dr Mac Keown said.
“Earth has a nitrogen-rich atmosphere, while Europe's environment has extremely low pressure and temperature.”
“In this study, we combined field observations with laboratory experiments to better simulate Europa's surface conditions.”
Looking to the future, the team plans to investigate how low pressure affects the formation of these structures and whether they could form under an icy crust, similar to how lava flows on Earth, creating smooth, viscous textures called pahoho.
Although geomorphology was the main focus of this research, the findings provide important clues about subsurface activity and habitability that are critical for future astrobiological research.
“Using numerical simulations of the brine reservoir, we have obtained constraints on the potential depth of the reservoir (up to 6 km or 3.7 miles below the surface) and its lifetime (up to several thousand years after impact),” Dr Lesage said.
“This is valuable information for future missions to search for habitable environments inside icy shells.”
teams results were published in Planetary Science Journal.
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Lauren E. Mac Keown etc.. 2025. Lake stars from Earth, analogous to the European spider from Mannan Crater. Planet. Sci. J 6, 279; two: 10.3847/PSJ/ae18a0
