Europa, one of Jupiter’s frozen moons, is recognized as a significant celestial body in the quest to identify potential extraterrestrial havens for life beyond our planet. The moon’s surface displays numerous formations that are theorized to stem from saline liquid sources deep within its icy shell, potentially offering the most accessible reservoirs of liquid water within our solar system. A particularly striking example is the star-shaped ‘spider’ feature located at the core of the Manannán crater, initially observed by NASA’s Galileo spacecraft. Planetary scientists have now proposed a novel hypothesis for the genesis of this spider-like geomorphology, derived from morphological scrutiny and preliminary analog modeling. Their proposition suggests that this formation may share origins with dendritic ‘lake stars,’ ephemeral features observed on terrestrial frozen lakes and ponds.
Manannán’s Damhán Alla geomorphologic map. Image credit: Mc Keown et al., doi: 10.3847/PSJ/ae18a0.
“This arachnoid formation might have come into existence through the expulsion of liquefied brines subsequent to the Manannán impact event,” stated Dr. Elodie Lesage, a researcher affiliated with the Planetary Science Institute.
“Consequently, it could provide insights into the subsurface characteristics and the composition of brines at the temporal juncture of the impact.”
Dr. Lesage and her research associates are also examining Martian ‘spiders,’ which are ramifying, arboreal formations that materialize in the regolith adjacent to the Martian south polar region.
This corpus of knowledge was then extrapolated to other planetary surfaces, including the cryosphere of Jupiter’s moon, Europa.
Whereas Martian spiders are sculpted by the sublimation of dust and sand driven by escaping gases beneath a transient dry ice layer, the team’s research on Europa posits that the ‘asterisk-shaped’ feature could have formed post-impact.
“Terrestrial lake stars are characterized by radial, branching geometries that develop when snowfall accumulates on frozen bodies of water. The consequent weight of the snow creates apertures within the ice, permitting water to infiltrate the snowpack, initiate melting, and subsequently spread in a manner dictated by favorable energy dynamics,” explained Dr. Lauren Mc Keown, a researcher from the University of Central Florida and NASA’s Jet Propulsion Laboratory.
“Our hypothesis for Europa is that a subterranean brine reservoir could have been mobilized by an impact event and subsequently disseminated through porous surface ice, thereby generating a comparable pattern.”
The researchers have informally designated Europa’s feature “Damhán Alla,” an Irish term translating to ‘spider,’ to differentiate it from its Martian counterparts.
To substantiate their hypothesis regarding the formation mechanism, they conducted both in-situ and laboratory investigations. These involved observing lake stars in Breckenridge, Colorado, and replicating the phenomenon within a cryogenic glovebox, utilizing Europa ice simulants chilled by liquid nitrogen.
“We facilitated the flow of water through these simulants under varied thermal conditions and observed the development of analogous star-like patterns even at extreme sub-zero temperatures (ranging from -100 degrees Celsius, or -148 degrees Fahrenheit), thereby lending credence to the possibility of a similar process occurring on Europa post-impact,” Dr. Mc Keown elaborated.
The scientific team developed a model illustrating the potential behavior of a brine pool situated beneath Europa’s surface following the impact event, culminating in the creation of an animation visualizing the entire process.
Current observations of Europa’s icy structures are confined to imagery captured by the Galileo spacecraft in 1998. However, the authors anticipate resolving this inquiry with higher-resolution imaging from the forthcoming Europa Clipper mission, a NASA probe slated for arrival in the Jovian system in April 2030.
“While lake stars have provided valuable perspectives, the environmental conditions on Earth diverge significantly from those on Europa,” Dr. Mc Keown cautioned.
“Our planet possesses a nitrogen-abundant atmosphere, whereas Europa’s milieu is characterized by exceptionally low pressure and temperature.”
“Within this investigation, we integrated observational data from terrestrial field studies with laboratory experimentation to more accurately simulate Europa’s surface milieu.”
Looking forward, the research group intends to explore the influence of reduced atmospheric pressure on the formation of these formations and ascertain whether they could coalesce beneath an icy crust, analogous to how lava flows on Earth give rise to smooth, undulating textures known as pahoehoe.
Although the primary focus of this study was geomorphological, the discoveries yield significant insights into subsurface dynamics and habitability, which are indispensable for subsequent astrobiological research endeavors.
“Through the application of numerical modeling to the brine reservoir, we were able to establish parameters for the reservoir’s potential depth (extending down to 6 kilometers, or 3.7 miles, below the surface) and its longevity (persisting for up to several thousand years post-impact),” Dr. Lesage explained.
“This data constitutes invaluable intelligence for future missions tasked with identifying potentially habitable environments within icy celestial bodies.”
The team’s findings have been officially documented and 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
