Europa, one of Jupiters largest moons, holds more liquid water beneath its frozen shell than all of Earths oceans combined, but the ocean is sealed away under thick ice that blocks sunlight and isolates it from the surface. That isolation creates a long standing puzzle: how materials processed by intense radiation at the surface could travel downward to feed any microbes that might inhabit the dark ocean.
Radiation from Jupiter constantly bombards Europas surface and reacts with salts and other materials to create oxidants and other useful nutrients. Several hypotheses have been advanced for how that nutrient rich ice might reach the ocean, but most focus on sideways or resurfacing motions of the shell rather than a sustained, downward transport.
To address this problem, Washington State University researcher Catherine Cooper and then WSU doctoral student Austin Green turned to an Earth process known as crustal delamination. On Earth, delamination occurs when a dense, chemically altered portion of crust becomes heavy enough to detach and sink into the underlying mantle, recycling material into the planets interior.
The team recognized that a similar process could operate in Europas ice shell because some regions of the moons surface are enriched in salts that make the ice denser than the surrounding, purer ice. Laboratory and modeling work from prior studies has also shown that impurities weaken the crystalline structure of ice, making those saltier patches mechanically less stable than clean ice.
Building on these ideas, Green and Cooper proposed that bands or patches of salt rich surface ice on Europa could detach from the surrounding shell once they are sufficiently weakened. Under the pull of gravity, the denser material would begin to sink into the shell interior in a delamination like process, potentially carrying surface generated oxidants and nutrients toward the ocean.
The researchers used computer models to test whether such salty, nutrient bearing ice could actually descend through the shell and how far it might travel. Their simulations indicate that, over a broad range of salt concentrations, dense surface ice can sink all the way to the base of the ice shell as long as there is at least modest weakening of the ice in the source region.
Model results suggest this sinking can proceed on relatively short geological timescales, implying that delamination of salt laden surface ice could provide a sustained conveyor for delivering nutrients into the ocean. If this process operates across many regions of the shell, it would represent an efficient, continuous pathway to recycle surface material into the subsurface ocean.
The work directly addresses a key habitability question for Europa by linking its radiation processed surface to its hidden ocean in a physically plausible way. It also offers a concrete prediction for how compositional and structural variations in the shell might map to zones of active material exchange between the surface and interior.
The findings align with central objectives of NASAs Europa Clipper mission, launched in 2024, which will perform multiple close flybys of the moon to investigate its ice shell, subsurface ocean, and potential to support life. Instruments on Europa Clipper are designed to probe shell thickness, internal structure, composition, and geological activity, all of which are relevant to testing the proposed delamination mechanism.
The study appears in The Planetary Science Journal and highlights how concepts from terrestrial geology can inspire new models for icy worlds in the outer solar system. By adapting the well known framework of crustal delamination to Europas conditions, the researchers provide a new lens for interpreting surface features and interior dynamics on one of the most promising locations for extraterrestrial life.
The project received partial support from NASA under Grant NNX15AH91G and used computing resources provided by the Center for Institutional Research Computing at Washington State University.
Research Report:Dripping to Destruction: Exploring Salt-driven Viscous Surface Convergence in Europa's Icy Shell
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