Strong tidal heating in an ultralow-viscosity zone at the core–mantle boundary of the Moon

Harada, Yuji; Goossens, Sander; Matsumoto, Koji; Yan, Jianguo; Ping, Jinsong; Noda, Hirotomo; Haruyama, Junichi

doi:10.1038/ngeo2211

Cited by 91 publications

(132 citation statements)

References 29 publications

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“…The equation system for a liquid layer (i.e., equations ‐) is significantly different from those used in several previous studies based on (visco) elasto‐gravitational theory [e.g., Saito , ; Jara‐Orué and Vermeersen , ; Harada et al , ]. Specifically, these studies use a two‐component equation system for a liquid layer.…”

Section: Theorymentioning

confidence: 99%

Tidal resonance in icy satellites with subsurface oceans

2015

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Tidal dissipation is a major heat source for the icy satellites of the giant planets. Several icy satellites likely possess a subsurface ocean underneath an ice shell. Previous studies of tidal dissipation on icy satellites, however, have either assumed a static ocean or ignored the effect of the ice lid on subsurface ocean dynamics. In this study, we examine inertial effects on tidal deformation of satellites with a dynamic ocean overlain by an ice lid based on viscoelasto-gravitational theory. Although ocean dynamics is treated in a simplified fashion, we find a resonant configuration when the phase velocity of ocean gravity waves is similar to that of the tidal bulge. This condition is achieved when a subsurface ocean is thin (<1 km). The enhanced deformation (increased h 2 and k 2 Love numbers) near the resonant configuration would lead to enhanced tidal heating in the solid lid. A static ocean formulation gives an accurate result only if the ocean thickness is much larger than the resonant thickness. The resonant configuration strongly depends on the properties of the shell, demonstrating the importance of the presence of a shell on tidal dissipation.

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Section: Theorymentioning

confidence: 99%

Tidal resonance in icy satellites with subsurface oceans

2015

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“…Thus, lunar core information can be deduced from deep moonquake events to some extent, even with the attenuation of S-waves. With the only located farside deep moonquake opposite to the Apollo station 15, a low-velocity core with a permissible radius in the ranges of 170-360 km (Nakamura et al, 1974) and 400-450 km (Sellers, 1992), respectively, as well as an attenuating, possibly molten region in the lower mantle (Nakamura, 2005;Weber et al, 2011;Harada et al, 2014), were inferred. Recent studies on lunar seismic data reduction indicated a small lunar core with radius in the range of $330-420 km, as well as being possibly molten Weber et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

Lunar core structure investigation: Implication of GRAIL gravity field model

Yan¹,

Xu²,

Li³

et al. 2015

Advances in Space Research

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“…Cooling of the core induced by upwelling IBC may have been at the origin of an early lunar dynamo (Cisowski et al, ; Shea & Fuller, ; Stegman et al, ). Furthermore, overturned IBC may also be responsible for the low‐viscosity zone inferred to be present above the CMB (Harada et al, ; Weber et al, ).…”

Section: Introductionmentioning

confidence: 99%

Overturn of Ilmenite‐Bearing Cumulates in a Rheologically Weak Lunar Mantle

Tosi

Schwinger

et al. 2019

JGR Planets

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The crystallization of the lunar magma ocean (LMO) determines the initial structure of the solid Moon. Near the end of the LMO crystallization, ilmenite‐bearing cumulates (IBC) form beneath the plagioclase crust. Being denser than the underlying mantle, IBC are prone to overturn, a hypothesis that explains several aspects of the Moon's evolution. Yet the formation of stagnant lid due to the temperature dependence of viscosity can easily prevent IBC from sinking. To infer the rheological conditions allowing IBC to sink, we calculated the LMO crystallization sequence and performed high‐resolution numerical simulations of the overturn dynamics. We assumed a diffusion creep rheology and tested the effects of reference viscosity, activation energy, and compositional viscosity contrast between IBC and mantle. The overturn strongly depends on reference viscosity and activation energy and is facilitated by a low IBC viscosity. For a reference viscosity of 1021 Pa s, characteristic of a dry rheology, IBC overturn cannot take place. For a reference viscosity of 1020 Pa s, the overturn is possible if the activation energy is a factor of 2–3 lower than the values typically assumed for dry olivine. These low activation energies suggest a role for dislocation creep. For lower‐reference viscosities associated with the presence of water or trapped melt, more than 95% IBC can sink regardless of the activation energy. Scaling laws for Rayleigh‐Taylor instability confirmed these results but also showed the need of numerical simulations to accurately quantify the overturn dynamics. Whenever IBC sink, the overturn occurs via small‐scale diapirs.

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Strong tidal heating in an ultralow-viscosity zone at the core–mantle boundary of the Moon

Cited by 91 publications

References 29 publications

Tidal resonance in icy satellites with subsurface oceans

Tidal resonance in icy satellites with subsurface oceans

Lunar core structure investigation: Implication of GRAIL gravity field model

Overturn of Ilmenite‐Bearing Cumulates in a Rheologically Weak Lunar Mantle

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