Thermal and Chemical Evolution of Small, Shallow Water Bodies in Europa's Ice Shell

Chivers, Chase; Buffo, Jacob; Schmidt, B. E.

doi:10.1029/2020je006692

Cited by 31 publications

(131 citation statements)

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“…We have shown that there exists a distinct and quantifiable relationship between the thermochemical environment of the ice–ocean interface at the time of solidification and the properties of the ice that forms. With the likelihood of ongoing hydrological activity within Europa’s ice shell in the form of lenses (B. E. Schmidt et al., 2011; Spaun et al., 1998), sills (Chivers et al., 2020; Craft et al., 2016; Manga & Michaut, 2017; Michaut & Manga, 2014), dikes, fractures (Dombard et al., 2013; Rudolph & Manga, 2009; Walker et al., 2014), and plumes (Jia et al., 2018; Sparks et al., 2016), understanding the characteristics of ice formed in an array of thermal environments is imperative in constraining the mechanical, dielectric, and eutectic properties of refrozen features. The presence of salt alters the rheological properties of ice (Assur, 1958; Durham et al., 2005; McCarthy et al., 2011) and could facilitate the reactivation of fractures as well as the dynamics of solid‐state convection in the ductile portion of the ice shell (e.g., Buffo et al., 2020).…”

Section: Discussionmentioning

confidence: 99%

“…The icy satellites of the outer solar system are some of the most enigmatic and inspirational bodies in planetary science, in large part due to their astrobiological potential (Des Marais et al., 2008; Hendrix et al., 2019; B. E. Schmidt, 2020). Ongoing geological activity and geomorphological features indicative of persistent subsurface water reservoirs suggests that these ice‐ocean worlds may house aqueous environments suitable for the formation and evolution of life (Chivers et al., 2020; Hand et al., 2009; Marion et al., 2003; C. D. Parkinson et al., 2008; Porco et al., 2006; B. E. Schmidt, 2020; B. E. Schmidt et al., 2011). One of the most promising of these bodies is Europa (Hand et al., 2007, 2009; Marion et al., 2003; B. E. Schmidt, 2020).…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of a Solidifying Icy Satellite Shell

2021

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The icy satellites of the outer solar system are some of the most enigmatic and inspirational bodies in planetary science, in large part due to their astrobiological potential (Des Marais et al., 2008;Hendrix et al., 2019;B. E. Schmidt, 2020). Ongoing geological activity and geomorphological features indicative of persistent subsurface water reservoirs suggests that these ice-ocean worlds may house aqueous environments suitable for the formation and evolution of life (

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dynamics of a Solidifying Icy Satellite Shell

2021

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“…HCN's density relationship with water and ice suggests that as a melt pond freezes from all directions, the HCN dynamics will operate differently at the bottom and upper interfaces. A key feature of our impact melt system is that it is a closed finite body of water, similar to the proposed pockets of water thought to cause chaos terrain on Europa (Schmidt et al 2011;Buffo et al 2020;Chivers et al 2021). SF2 assumes the mushy layer is atop an infinite ocean and that the rejected impurities will never significantly affect the bulk concentration of the ocean; however, the bulk concentration of a melt pond will become progressively more concentrated as it freezes.…”

Section: Application To Titanmentioning

confidence: 96%

“…Unlike salt, HCN is less dense than water and ice (Table 2; Haynes 2011). This relationship will invert the system such that impurities are buoyantly removed at the base of the melt pond, while at the top, gravity will not drive the removal of impurities (Chivers et al 2021). Similar scenarios have been studied in terrestrial magma chambers, where low-density melt is concentrated in the porous roof magma-rock interface during solidification (Worster 1990).…”

Section: Application To Titanmentioning

confidence: 99%

“…Here, we constrain how much HCN will become trapped in the ice versus rejected into the remaining liquid reservoir under the conditions predicted for fresh impact crater melts on Titan. We use the planetary ice model SlushFund2.0-v2 (SF2; Buffo et al 2020) and a heat transfer model (Chivers et al 2021) to track the concentrations of molecular impurities, both within the ice and the residual melt, as the melt pond refreezes, providing improved estimates of organic material distribution in Titan environments for future planetary exploration.…”

Section: Introductionmentioning

confidence: 99%

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Modeling the Distribution of Organic Carbon and Nitrogen in Impact Crater Melt on Titan

et al. 2022

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Titan is a chemically rich world that provides a natural laboratory for the study of the origin of life. Titan’s atmospherically derived C x H y N z molecules have been shown to form amino acids when mixed with liquid water, but the transition from prebiotic chemistry to the origin of life is not well understood. Investigating this prebiotic environment on Titan is one of the primary motivations behind NASA’s Dragonfly mission. One of its objectives is to visit the 80 km diameter Selk crater, where a melt sheet of liquid water would have formed during the impact cratering process. Organic molecules on Titan’s surface could have mixed with this water, forming molecules of prebiotic interest. Constraining how this material becomes trapped in the refreezing ice is necessary for Dragonfly to effectively target and interpret the samples it aims to acquire. In this work, we adapt the planetary ice model of Buffo et al. to Titan conditions to track how organic molecules will become trapped within the ice of the freezing melt sheet. We use HCN as a model impurity because of its abundance on Titan and its propensity to form amino acids in aqueous solutions. We show that without hydrolysis, HCN will be concentrated in the upper and middle portions of the resolidified melt sheet. In a closed system like Selk crater, the highest concentration of HCN appears 75% of the way into the frozen melt pond (relative to the surface), but HCN should be accessible at high concentrations nearer the surface as well.

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Entrainment and Dynamics of Ocean-derived Impurities within Europa's Ice Shell

Buffo

Schmidt

Huber

et al. 2020

Preprint

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Compositional heterogeneities within Europa's ice shell likely impact the dynamics and habitability of the ice and subsurface ocean, but the total inventory and distribution of impurities within the shell are unknown. In sea ice on Earth, the thermochemical environment at the ice-ocean interface governs impurity entrainment into the ice. Here, we simulate Europa's ice-ocean interface and bound the impurity load (1.053-14.72 g/kg [parts per thousand weight percent, or ppt] bulk ice shell salinity) and bulk salinity profile of the ice shell. We derive constitutive equations that predict ice composition as a function of the ice shell thermal gradient and ocean composition. We show that evolving solidification rates of the ocean and hydrologic features within the shell produce compositional variations (ice bulk salinities of 5-50% of the ocean salinity) that can affect the material properties of the ice. As the shell thickens, less salt is entrained at the ice-ocean interface, which implies Europa's ice shell is compositionally homogeneous below ~1 km. Conversely, the solidification of water filled fractures or lenses introduces substantial compositional variations within the ice shell, creating gradients in mechanical and thermal properties within the ice shell that could help initiate and sustain geological activity. Our results suggest that ocean materials entrained within Europa's ice shell affect the formation of geologic terrain and that these structures could be confirmed by planned spacecraft observations. Plain Language Summary Europa, the second innermost moon of Jupiter, likely houses an interior ocean that could provide a habitat for life. This ocean resides beneath a 10-to >30-km-thick ice shell which could act as a barrier or conveyor for ocean-surface material transport that could render the ocean chemistry either hospitable or unfavorable for life. Additionally, material impurities in the ice shell will alter its physical properties and thus affect the global dynamics of the moon's icy exterior. That said, few of the interior properties of the ice shell or ocean have been directly measured. On Earth, the composition of ocean-derived ice is governed by the chemistry of the parent liquid and the rate at which it forms. Here, we extend models of sea ice to accommodate the Europa ice-ocean environment and produce physically realistic predictions of Europa's ice shell composition and the evolution of water bodies (fractures and lenses) within the shell. Our results show that the thermal gradient of the ice and the liquid composition affect the formation and evolution of geologic features in ways that could be detectable by future spacecraft (e.g., by ice penetrating radar measurements made by Europa Clipper).

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Thermal and Chemical Evolution of Small, Shallow Water Bodies in Europa's Ice Shell

Abstract: Europa's geologically young surface has been modified by a myriad of geologic processes over at least the last 100 Myr (Bierhaus et al., 2009). Of the many resulting geologic features, the youngest appear low albedo and reddish in color, likely due to hydrated salts (e.g.,

Cited by 31 publications

References 82 publications

Dynamics of a Solidifying Icy Satellite Shell

Dynamics of a Solidifying Icy Satellite Shell

Modeling the Distribution of Organic Carbon and Nitrogen in Impact Crater Melt on Titan

Entrainment and Dynamics of Ocean-derived Impurities within Europa's Ice Shell

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