Chivers
Chase J.
Chivers
Chase J.
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ArticleGeometry of freezing impacts ice composition: implications for icy satellites(American Geophysical Union, 2023-03-14) Buffo, Jacob J. ; Meyer, Colin R. ; Chivers, Chase J. ; Walker, Catherine C. ; Huber, Christian ; Schmidt, Britney E.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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ArticleIce-Ocean interactions on ocean worlds influence ice shell topography(American Geophysical Union, 2024-02-13) Lawrence, Justin D. ; Schmidt, Britney Elyce ; Buffo, Jacob J. ; Washam, Peter M. ; Chivers, Chase J. ; Miller, SaraThe freezing point of water is negatively dependent on pressure; therefore in any ocean without external forcing it is warmest at the surface and grows colder with depth. Below floating ice on Earth (e.g., ice shelves or sea ice), this pressure dependence combines with gradients in the ice draft to drive an ice redistribution process termed the “ice pump”: submerged ice melts, upwells, and then refreezes at shallower depths. Ice pumping is an exchange process between the ocean and overhead ice that results in unique ice compositions and textures and influences the distribution of sub-ice habitats on Earth. Here, we scale recent observations from Earth's ice shelves to planetary conditions and find that ice pumping is expected for a wide range of possible sub-ice shell pressures and salinity at other ocean worlds such as Europa and Enceladus. We show how ice pumping would affect hypothetical basal ice shell topography and ice thickness under varying ocean conditions and demonstrate how remote sensing of the ice shell draft can be used to estimate temperature gradients in the upper ocean ahead of in situ exploration. For example, the approximately 22 km gradient observed in Enceladus' ice shell draft between the south pole and the equator suggests a temperature differential of 0.18 K at the base of the ice shell. These concepts can extend the interpretation of observations from upcoming ocean world missions, and link ice shell topography to ice-ocean material exchange processes that may prove important to overall ocean world habitability.
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ArticleInvestigating Europa’s habitability with the Europa Clipper(Springer, 2023-11-29) Vance, Steven D. ; Craft, Kathleen L. ; Shock, Everett ; Schmidt, Britney E. ; Lunine, Jonathan I. ; Hand, Kevin P. ; McKinnon, William B. ; Spiers, Elizabeth M. ; Chivers, Chase J. ; Lawrence, Justin D. ; Wolfenbarger, Natalie ; Leonard, Erin J. ; Robinson, Kirtland J. ; Styczinski, Marshall J. ; Persaud, Divya M. ; Steinbrugge, Gregor ; Zolotov, Mikhail Y. ; Quick, Lynnae C. ; Scully, Jennifer E. C. ; Becker, Tracy M. ; Howell, Samuel M. ; Clark, Roger N. ; Dombard, Andrew J. ; Glein, Christopher R. ; Mousis, Olivier ; Sephton, Mark A. ; Castillo-Rogez, Julie ; Nimmo, Francis ; McEwen, Alfred S. ; Gudipati, Murthy S. ; Jun, Insoo ; Jia, Xianzhe ; Postberg, Frank ; Soderlund, Krista M. ; Elder, Catherine M.The habitability of Europa is a property within a system, which is driven by a multitude of physical and chemical processes and is defined by many interdependent parameters, so that its full characterization requires collaborative investigation. To explore Europa as an integrated system to yield a complete picture of its habitability, the Europa Clipper mission has three primary science objectives: (1) characterize the ice shell and ocean including their heterogeneity, properties, and the nature of surface–ice–ocean exchange; (2) characterize Europa’s composition including any non-ice materials on the surface and in the atmosphere, and any carbon-containing compounds; and (3) characterize Europa’s geology including surface features and localities of high science interest. The mission will also address several cross-cutting science topics including the search for any current or recent activity in the form of thermal anomalies and plumes, performing geodetic and radiation measurements, and assessing high-resolution, co-located observations at select sites to provide reconnaissance for a potential future landed mission. Synthesizing the mission’s science measurements, as well as incorporating remote observations by Earth-based observatories, the James Webb Space Telescope, and other space-based resources, to constrain Europa’s habitability, is a complex task and is guided by the mission’s Habitability Assessment Board (HAB).