Layering by Double‐Diffusive Convection in the Subsurface Oceans of Europa and Enceladus

Wong, Teresa; Hansen, Ulrich; Wiesehöfer, T.; McKinnon, W. B.

doi:10.1029/2022je007316

Cited by 8 publications

(6 citation statements)

References 71 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This enhancement can be thought of as being roughly equivalent to an increase in κ that allows a salinity gradient with N 2 ∼ 10 −8 s −2 to remain Ledoux stable (Equation ( 43)). Numerical simulations confirm a strong enhancement of heat transport by double-diffusive convection in the regime of icy satellites (Wong et al 2022), where, contrary to the gas giant planets, the kinematic viscosity ν is typically larger than the thermal diffusivity κ. Double-diffusive convection is typically accompanied by evolution of the compositional gradient (Radko 2013;Wong et al 2022), thus further studies are required to understand better the timescales imposed on the evolution of salinity profiles in icy satellites. Saturn's radius.…”

Section: Ocean Stability To Overturning Convectionmentioning

confidence: 79%

Resonant Stratification in Titan’s Global Ocean

Idini,

Nimmo

2024

Planet. Sci. J.

View full text Add to dashboard Cite

Titan’s ice shell floats on top of a global ocean, as revealed by the large tidal Love number k 2 = 0.616 ± 0.067 registered by Cassini. The Cassini observation exceeds the predicted k 2 by one order of magnitude in the absence of an ocean, and is 3σ away from the predicted k 2 if the ocean is pure water resting on top of a rigid ocean floor. Previous studies demonstrate that an ocean heavily enriched in salts (salinity S ≳ 200 g kg−1) can explain the 3σ signal in k 2. Here we revisit previous interpretations of Titan’s large k 2 using simple physical arguments and propose a new interpretation based on the dynamic tidal response of a stably stratified ocean in resonance with eccentricity tides raised by Saturn. Our models include inertial effects from a full consideration of the Coriolis force and the radial stratification of the ocean, typically neglected or approximated elsewhere. The stratification of the ocean emerges from a salinity profile where the salt concentration linearly increases with depth. We find multiple salinity profiles that lead to the k 2 required by Cassini. In contrast with previous interpretations that neglect stratification, resonant stratification reduces the bulk salinity required by observations by an order of magnitude, reaching a salinity for Titan’s ocean that is compatible with that of Earth’s oceans and close to Enceladus’ plumes. Consequently, no special process is required to enrich Titan’s ocean to a high salinity as previously suggested.

show abstract

Section: Ocean Stability To Overturning Convectionmentioning

confidence: 79%

Resonant Stratification in Titan’s Global Ocean

Idini,

Nimmo

2024

Planet. Sci. J.

View full text Add to dashboard Cite

show abstract

“…As discussed above, any ice thickness variation would need to be actively maintained by freezing and melting to compensate the viscous flow, and the associated brine and fresh‐water injections could then drive its own large‐scale circulation (Kang, Mittal, et al., 2022; Lobo et al., 2021). Including salinity effects also adds the possibility of double‐diffusive convection (Vance & Brown, 2005; Wong et al., 2022). The large‐scale topography due to ice thickness variations could also induce its own feedback on the ocean dynamics.…”

Section: Resultsmentioning

confidence: 99%

Europa's Ocean Translates Interior Tidal Heating Patterns to the Ice‐Ocean Boundary

Lemasquerier,

Bierson,

Soderlund

2023

AGU Advances

View full text Add to dashboard Cite

The circulation in Europa's ocean determines the degree of thermal, mechanical and chemical coupling between the ice shell and the silicate mantle. Using global direct numerical simulations, we investigate the effect of heterogeneous tidal heating in the silicate mantle on rotating thermal convection in the ocean and its consequences on ice shell thickness. Under the assumption of no salinity or ocean‐ice shell feedbacks, we show that convection largely transposes the latitudinal variations of tidal heating from the seafloor to the ice, leading to a higher oceanic heat flux in polar regions. Longitudinal variations are efficiently transferred when boundary‐driven thermal winds develop, but are reduced in the presence of strong zonal flows and may vanish in planetary regimes. If spatially homogeneous radiogenic heating is dominant in the silicate mantle, the ocean's contribution to ice shell thickness variations is negligible compared to tidal heating within the ice. If tidal heating is instead dominant in the mantle, the situation is reversed and the ocean controls the pole‐to‐equator thickness contrast, as well as possible longitudinal variations.

show abstract

“…First, even a vigorously convecting ocean is not isothermal, with adiabatic gradients resulting in temperature contrasts on the order of a few kelvin across the convective layer due to heat transfer from the radioactive core and into the overlying ice (e.g., Bire et al 2022). Second, although thick oceans are expected to be efficiently mixed (Soderlund et al 2014), heterogeneities in temperature and composition with depth (stratification) and/or latitude may arise due to, e.g., the icy world's spin (Zhu et al 2017;Soderlund 2019;Zeng & Jansen 2021), latitudinal variations in ice shell thickness and distribution of tidal dissipation (Kang et al 2022a(Kang et al , 2022b, and competing effects of temperature and salinity on density, which result in doublediffusive convection (Vance & Brown 2005;Travis et al 2012;Wong et al 2022).…”

Section: )mentioning

confidence: 99%

Salt Distribution from Freezing Intrusions in Ice Shells on Ocean Worlds: Application to Europa

Naseem,

Neveu,

Howell

et al. 2023

Planet. Sci. J.

View full text Add to dashboard Cite

Several icy moons and dwarf planets appear to have hosted subsurface liquid water. Liquid water intruding upwards into the icy outer shells of these worlds freezes, forming ice and (from ocean solutes) non-ice solids. Here, we model concentrated aqueous solutions below 273 K to simulate the compositional evolution of freezing spherical intrusions. Starting solutions are based on five previously reported compositional end members for Europa’s ocean. For moderate-pH end members dominated by chloride, sulfate, and/or carbonate, the solids formed include Ca-, Mg-, and Na-sulfates and -carbonates, as well as Na- and K-chlorides. For silica-rich, high-pH end members, abundant amorphous silica forms with, potentially, similarly abundant NaOH and KOH. We further develop a new numerical model to compute the spatial distribution of the formed solids and residual brine as freezing progresses. If non-ice solids settle to the bottom, their deposits tend to have stacked hourglass shapes, widening each time the crystallization temperature of a new solid is reached. We discuss the applicability of this model to vertical fractures and global freezing of a subsurface ocean. These results inform (i) how compositional heterogeneities may affect the thermophysical properties of ice shells, which in turn influence convective and cryovolcanic transport, (ii) the compatibility of brine pockets with physicochemical conditions suitable for microbial life, and (iii) possible measurements of compositional heterogeneities within ice shells by spacecraft such as NASA’s Europa Clipper and ESA’s JUICE missions. The methodology developed here is applicable to other ice-covered ocean worlds.

show abstract

Layering by Double‐Diffusive Convection in the Subsurface Oceans of Europa and Enceladus

Cited by 8 publications

References 71 publications

Resonant Stratification in Titan’s Global Ocean

Resonant Stratification in Titan’s Global Ocean

Europa's Ocean Translates Interior Tidal Heating Patterns to the Ice‐Ocean Boundary

Salt Distribution from Freezing Intrusions in Ice Shells on Ocean Worlds: Application to Europa

Contact Info

Product

Resources

About