Ice Shell Structure and Composition of Ocean Worlds: Insights from Accreted Ice on Earth

Wolfenbarger, Natalie S.; Buffo, Jacob; Soderlund, K. M.; Blankenship, D. D.

doi:10.1002/essoar.10507059.3

Cited by 3 publications

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“…Wolfenbarger et al. (2022) noted that there was a similarity between the value they derived for the effective equilibrium solute distribution coefficient and the critical porosity for congelation sea ice. They interpreted this similarity as evidence supporting that a percolation threshold likely governed the effective equilibrium solute distribution coefficient.…”

Section: Resultsmentioning

confidence: 79%

“…Although we are able to estimate the brine volume fraction for bulk ice salinities up to the eutectic salinity, the bulk salinity of Europa's ice shell is limited by the efficiency of salt entrainment from the ocean (Buffo et al., 2020; Wolfenbarger et al., 2022). The bulk salinity of Europa's ice shell resulting from equilibrium freezing of the ocean has been estimated to be as low as ∼0.1% and as high as ∼10% of the ocean salinity depending on the mechanism of ice formation and the microstructural interface morphology (Wolfenbarger et al., 2022). More locally, cryoconcentration of perched lakes or sills could generate regions of enhanced bulk salinity up to the eutectic salinity (Chivers et al., 2021).…”

Section: Resultsmentioning

confidence: 99%

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Compositional Controls on the Distribution of Brine in Europa's Ice Shell

et al. 2022

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The presence of liquid water has long guided the search for life beyond Earth (Des Marais et al., 2003). Once thought to be confined to the "Goldilocks zone," vast oceans have been inferred to exist beneath the thick ice shells of moons in the outer solar system (Hand et al., 2020). Although these sub-ice oceans represent the most compelling potential habitats in the outer solar system (Shematovich, 2018), they are covered by ice shells that can range from kilometers to hundreds of kilometers thick (Soderlund et al., 2020). Impurities within the ice shell, such as salts, acids, or organic compounds, could allow for liquid water to remain stable at temperatures well below that predicted by the pressure-melting curve of pure water (Marion et al., 2003(Marion et al., , 2005Ruiz et al., 2007). These impurities support the formation of intra-ice shell brine pockets, which could represent potential habitats that might be more accessible than the sub-ice ocean (Kargel et al., 2000;Marion et al., 2003).Estimating the distribution of brine in an ice shell represents an important step in studying the habitability of ocean worlds. The brine volume fraction governs a number of bulk ice thermophysical properties, such as density, thermal conductivity, specific heat capacity, and viscosity (Petrich & Eicken, 2017). These thermophysical properties in turn govern processes of surface-ice-ocean exchange (e.g., solid-state convection, subduction, diapirism),

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Section: Resultsmentioning

confidence: 79%

Section: Resultsmentioning

confidence: 99%

Compositional Controls on the Distribution of Brine in Europa's Ice Shell

et al. 2022

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“…In addition, polynyas, open ocean areas in ice-covered seas, are regions of salt rejection into the underlying ocean as ice forms, a mechanism that can entrain chemical and molecular components at the ice-ocean interface (Greely et al, 1998;Arrigo et al, 2012;Meredith et al, 2019). Notably, Wolfenbarger et al (2022) conclude that ice formed in the low temperature gradient environment beneath ice shelves in Antarctica may be a more relevant analog than sea ice for icy world shell dynamics, providing an alternate hypothesis for further Earth polar studies.…”

Section: Ocean Worlds Workhop Goals Questions and Summarymentioning

confidence: 90%

“…For example, formation of frazil ice and congelation (sub-ice) growth beneath ice shelves are relevant to studies of icy worlds (Wolfenbarger et al, 2022). Frazil ice is composed of loose, randomly arranged ice crystals that form in supercooled turbulent water (Figure 3), and congelation ice forms on the bottom of an established ice cover.…”

Section: Ocean Worlds Workhop Goals Questions and Summarymentioning

confidence: 99%

“…This mechanism could entrain chemical and molecular components at the ice-ocean interface or produce a subsurface pool of material in the upper ocean region in icy worlds that could act as potential sites for chemosynthetic life. Alternatively, Wolfenbarger et al (2022) suggest that congelation ice produced in low temperature gradients may be more relevant to understanding icy world shell dynamics than sea ice studies. Ongoing climate change will impact ice composition and associated growth mechanisms on Earth; thus, studies of variable mechanisms for ice formation and salt extrusion should provide valuable information on icy world systems.…”

Section: Analogs On Earth To Icy Worlds That Are Influenced By Climat...mentioning

confidence: 99%

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Applying Understanding of Earth Systems, Including Climate Change, to Exploration of Other Ocean Worlds

Grebmeier¹

2022

Oceanog

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Earth’s polar and deep ocean systems and how they are affected by environmental changes provide analogs for understanding key processes acting in other ocean worlds, from physical and geological dynamics to chemical and biological processes. Subglacial lakes in Antarctica that are overlain by multiple kilometers of ice, as well as polar ice shelves underlain by subsurface areas of the ocean, are key sites for studying processes operating at ice-water and rock-ocean interfaces on Earth and on icy worlds. Hydrothermal vents at the seafloor release chemicals that provide energy for life and are also key areas for cross-linked Earth and planetary studies relevant to deep oceans dynamics. The presence of chemosynthetic microbes that are then consumed by multicellular life forms provide an analog for examining the potential existence of life in some subregions within ocean worlds. Here, we discuss the various Earth system processes that may have analogs on other ocean worlds and the benefits of collaborative Earth and planetary science investigations.

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Geometry of Freezing Impacts Ice Composition: Implications for Icy Satellites

et al. 2023

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Non‐ice impurities within the ice shells of ocean worlds (e.g., Europa, Enceladus, Titan, Ganymede) are believed to play a fundamental role in their geophysics and habitability and may become a surface expression of subsurface ocean properties. Heterogeneous entrainment and distribution of impurities within planetary ice shells have been proposed as mechanisms that can drive ice shell overturns, generate diverse geological features, and facilitate ocean‐surface material transport critical for maintaining a habitable subsurface ocean. However, current models of ice shell composition suggest that impurity rejection at the ice‐ocean interface of thick contemporary ice shells will be exceptionally efficient, resulting in relatively pure, homogeneous ice. As such, additional mechanisms capable of facilitating enhanced and heterogeneous impurity entrainment are needed to reconcile the observed physicochemical diversity of planetary ice shells. Here we investigate the potential for hydrologic features within planetary ice shells (sills and basal fractures), and the unique freezing geometries they promote, to provide such a mechanism. By simulating the two‐dimensional thermal and physicochemical evolution of these hydrological features as they solidify, we demonstrate that bottom‐up solidification at sill floors and horizontal solidification at fracture walls generate distinct ice compositions and provide mechanisms for both enhanced and heterogeneous impurity entrainment. We compare our results with magmatic and metallurgic analogs that exhibit similar micro‐ and macroscale chemical zonation patterns during solidification. Our results suggest variations in ice‐ocean/brine interface geometry could play a fundamental role in introducing compositional heterogeneities into planetary ice shells and cryoconcentrating impurities in (re)frozen hydrologic features.

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Ice Shell Structure and Composition of Ocean Worlds: Insights from Accreted Ice on Earth

Cited by 3 publications

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Compositional Controls on the Distribution of Brine in Europa's Ice Shell

Compositional Controls on the Distribution of Brine in Europa's Ice Shell

Applying Understanding of Earth Systems, Including Climate Change, to Exploration of Other Ocean Worlds

Geometry of Freezing Impacts Ice Composition: Implications for Icy Satellites

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