Turbulent Drag at the Ice‐Ocean Interface of Europa in Simulations of Rotating Convection: Implications for Nonsynchronous Rotation of the Ice Shell

Hay, H. C. F. C.; Fenty, Ian; Pappalardo, R.; Nakayama, Yoshihiro

doi:10.1029/2022je007648

Cited by 5 publications

(19 citation statements)

References 104 publications

(205 reference statements)

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“…The disparity between our findings and Hay et al ( 17 ) is notably more pronounced. Their numerical simulations have ocean current speeds in the range of O(0.1 to 1) m/s, resulting in a surface stress estimate of O(1) Pa.…”

Section: Resultscontrasting

confidence: 99%

“…The ice shell is assumed to be in equilibrium state so that the freezing/ melting rate is in balance with the flattening tendency induced by ice flow ( 24), but Ashkenazy et al (16) prescribes a flat ice shell and allow the ice shell to freely freeze or melt, which leads to much stronger salinity flux from the ice and thereby larger salinity contrast and stronger thermal wind. The disparity between our findings and Hay et al (17) is notably more pronounced. Their numerical simulations have ocean current speeds in the range of O(0.1 to 1) m/s, resulting in a surface stress estimate of O(1) Pa.…”

Section: Sensitivity Tests and Comparison With Previous Workcontrasting

confidence: 99%

“…Although the magnitude of the zonal flow is likely overestimated in the numerical simulations of ( 17), as acknowledged in that study, the qualitative results are still useful and inspiring. Further, (17) proposed a scaling that connects the surface stress with the kinetic energy of the system. Substituting the kinetic energy obtained here to the scaling would lead to a surface stress that is within a factor of 10 of our prediction.…”

Section: Sensitivity Tests and Comparison With Previous Workmentioning

confidence: 99%

“…The rate of ice shell NSR contains useful information about the subsurface ocean. While it is possible to drive NSR through the tidal torques associated with the eccentric orbit ( 15 ), the ocean may transport angular momentum between the ice shell and ocean, causing them to rotate relative to one another ( 16 , 17 ). Knowing the ocean-driven NSR rate and the rheology of the ice shell would then allow one to estimate the global-mean surface stress from the ocean, which then can be used to put constraints on the ocean boundary dissipation, energetics, flow speed, and even meridional density variations, as to be shown in this work.…”

Section: Introductionmentioning

confidence: 99%

“…Knowing the ocean-driven NSR rate and the rheology of the ice shell would then allow one to estimate the global-mean surface stress from the ocean, which then can be used to put constraints on the ocean boundary dissipation, energetics, flow speed, and even meridional density variations, as to be shown in this work. Earlier this year, Ashkenazy et al ( 16 ) and Hay et al ( 17 ) provided the first theoretical and numerical estimates for the ice-ocean torque and drift speed of the ice shell. They find that Europa ice shell may undergo negligible drift, constant drift, or oscillatory drift depending on the relaxation timescale of the ice shell and on the ocean currents and that at least 1-cm/s jet speed is required for ice-ocean torque to drive NSR, respectively.…”

Section: Introductionmentioning

confidence: 99%

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Nonsynchronous rotation of icy moon ice shells: The thermal wind perspective

Kang

2024

Sci. Adv.

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The ice shells of icy satellites have been hypothesized to undergo nonsynchronous rotation (NSR) under the influence of tidal torques and/or ocean currents. In this work, the author proposes that the thermal wind relationship can be combined with geostrophic turbulence theory to predict ocean stress onto the ice shell inside the tangent cylinder. High-resolution numerical simulations validate the prediction within a factor of 2. For the prediction to be valid, the rotation effect must dominate (Rossby number < 1), and the upper ocean should be stratified. The latter can be achieved with sufficiently large ice thickness variations [the threshold for Europa is O(100) m]. Using this framework, once the ice rheology, thickness variations and NSR rate are determined, one may be able to estimate the ocean overturn timescale and put constraints on the ocean vertical diffusivity or the heat flux originating from the silicate core.

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Section: Resultscontrasting

confidence: 99%

Section: Sensitivity Tests and Comparison With Previous Workcontrasting

confidence: 99%

Section: Sensitivity Tests and Comparison With Previous Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Nonsynchronous rotation of icy moon ice shells: The thermal wind perspective

Kang

2024

Sci. Adv.

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Geophysical Characterization of the Interiors of Ganymede, Callisto and Europa by ESA’s JUpiter ICy moons Explorer

Van Hoolst,

Tobie,

Vallat

et al. 2024

Space Sci Rev

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The JUpiter ICy moons Explorer (JUICE) of ESA was launched on 14 April 2023 and will arrive at Jupiter and its moons in July 2031. In this review article, we describe how JUICE will investigate the interior of the three icy Galilean moons, Ganymede, Callisto and Europa, during its Jupiter orbital tour and the final orbital phase around Ganymede. Detailed geophysical observations about the interior of the moons can only be performed from close distances to the moons, and best estimates of signatures of the interior, such as an induced magnetic field, tides and rotation variations, and radar reflections, will be obtained during flybys of the moons with altitudes of about 1000 km or less and during the Ganymede orbital phase at an average altitude of 490 km. The 9-month long orbital phase around Ganymede, the first of its kind around another moon than our Moon, will allow an unprecedented and detailed insight into the moon’s interior, from the central regions where a magnetic field is generated to the internal ocean and outer ice shell. Multiple flybys of Callisto will clarify the differences in evolution compared to Ganymede and will provide key constraints on the origin and evolution of the Jupiter system. JUICE will visit Europa only during two close flybys and the geophysical investigations will focus on selected areas of the ice shell. A prime goal of JUICE is the characterisation of the ice shell and ocean of the Galilean moons, and we here specifically emphasise the synergistic aspects of the different geophysical investigations, showing how different instruments will work together to probe the hydrosphere. We also describe how synergies between JUICE instruments will contribute to the assessment of the deep interior of the moons, their internal differentiation, dynamics and evolution. In situ measurements and remote sensing observations will support the geophysical instruments to achieve these goals, but will also, together with subsurface radar sounding, provide information about tectonics, potential plumes, and the composition of the surface, which will help understanding the composition of the interior, the structure of the ice shell, and exchange processes between ocean, ice and surface. Accurate tracking of the JUICE spacecraft all along the mission will strongly improve our knowledge of the changing orbital motions of the moons and will provide additional insight into the dissipative processes in the Jupiter system. Finally, we present an overview of how the geophysical investigations will be performed and describe the operational synergies and challenges.

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Spin–orbit coupling of Europa’s ice shell and interior

Burnett

Hayne

2023

Icarus

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Turbulent Drag at the Ice‐Ocean Interface of Europa in Simulations of Rotating Convection: Implications for Nonsynchronous Rotation of the Ice Shell

Cited by 5 publications

References 104 publications

Nonsynchronous rotation of icy moon ice shells: The thermal wind perspective

Nonsynchronous rotation of icy moon ice shells: The thermal wind perspective

Geophysical Characterization of the Interiors of Ganymede, Callisto and Europa by ESA’s JUpiter ICy moons Explorer

Spin–orbit coupling of Europa’s ice shell and interior

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