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 hosts many features proposed to originate from brine sources within its icy shell, which may represent the most accessible liquid water bodies within our Solar System. An intriguing possible example is the asterisk-shaped ‘spider’ at the center of Manannán crater, identified by NASA’s Galileo mission. Planetary scientists now present a new formation hypothesis for this spider-like feature based on morphological analysis and preliminary analog modeling. They suggest that the feature may originate from a process similar to that forming dendritic ‘lake stars,’ seasonal features found on frozen ponds and lakes on Earth.
Manannán’s Damhán Alla geomorphologic map. Image credit: Mc Keown et al., doi: 10.3847/PSJ/ae18a0.
“This spider-like feature might have formed through the eruption of melted brines following the Manannán impact,” said Dr. Elodie Lesage, a researcher at the Planetary Science Insititute.
“This would mean that it can inform us on subsurface properties and brine composition at the time of the impact.”
Dr. Lesage and colleagues also study Martian ‘spiders,’ which are branching, tree-like features that form in the regolith near Mars’ south pole.
They applied that knowledge to other planetary surfaces, including Jupiter’s icy moon Europa.
While Martian spiders form when dust and sand are eroded by escaping gas below a seasonal dry ice layer, the team’s Europa work asserts that the ‘asterisk-shaped’ feature may have formed after 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 in a way that is energetically favorable,” said Dr. Lauren Mc Keown, a researcher at the University of Central Florida and NASA’s Jet Propulsion Laboratory.
“On Europa, we believe a subsurface brine reservoir could have erupted after an impact and spread through porous surface ice, producing a similar pattern.”
The researchers informally named Europa’s feature Damhán Alla, Irish for ‘spider,’ to distinguish it from Martian spider formations.
To test their formation hypothesis, they also conducted field and lab experiments, observing lake stars in Breckenridge, Colorado, and recreating the process in a cryogenic glovebox, using Europa ice simulants cooled with liquid nitrogen.
“We flowed water through these simulants under different temperatures and found that similar star-like patterns formed even under extremely cold temperatures (minus 100 degrees Celsius, or minus 148 degrees Fahrenheit), supporting the idea that the same mechanism could occur on Europa after impact,” Dr. Mc Keown said.
The scientists modeled how a brine pool might behave beneath Europa’s surface after this impact, and the team created an animation illustrating the process.
Observations of Europa’s icy feature have been limited to images from the Galileo spacecraft from 1998, but the authors hope to resolve this question with higher-resolution imagery from the Europa Clipper mission, a NASA spacecraft scheduled to arrive at the Jupiter system in April 2030.
“While lake stars have provided valuable insight, Earth’s conditions are very different from Europa’s,” Dr. Mc Keown said.
“Earth has a nitrogen-rich atmosphere, while Europa’s environment is extremely low in pressure and temperature.”
“In this study, we combined field observations with lab experiments to better simulate Europa’s surface conditions.”
Looking ahead, the team plans to investigate how low pressure affects the formation of these features and whether they could form beneath an icy crust, similar to how lava flows on Earth to create smooth, ropy textures called pahoehoe.
Although geomorphology was the main focus of this study, the findings offer important clues about subsurface activity and habitability, which are crucial for future astrobiology research.
“Using numerical modelling of the brine reservoir, we obtained constraints on the reservoir potential depth (up to 6 km, or 3.7 miles, below the surface) and lifetime (up to a few thousands of years post-impact),” Dr. Lesage said.
“This is valuable information for future missions looking for habitable environments within icy shells.”
The team’s results were published in the Planetary Science Journal.
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Lauren E. Mc Keown et al. 2025. Lake Stars as an Earth Analog for Europa’s Manannán Crater Spider Feature. Planet. Sci. J 6, 279; doi: 10.3847/PSJ/ae18a0
