Dynamics and Thermal History of the Terrestrial Planets, the Moon, and Io

Breuer, D.; Moore, W. B.

doi:10.1016/b978-0-444-53802-4.00173-1

Cited by 69 publications

(67 citation statements)

References 479 publications

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“…Interestingly, the geophysically constrained internal temperatures are not too far below the solidus temperature (see Figure ). This suggests that “localized” features such as a large plume below Tharsis (Harder & Christensen, ; Keller & Tackley, ; Roberts & Zhong, ; Šrámek & Zhong, ; Zhong, ; Zhong & Zuber, ) would allow for regional magmatism to occur without being widespread as observed on, for example, Io (Breuer & Moore, ) and Venus (Ivanov & Head, ). In the simulations performed here, we neglect the implications of a giant impact as a means of forming most of the north‐south crustal dichotomy (Golabek et al, ; Marinova et al, ; Nimmo et al, ; Reese et al, ).…”

Section: Geodynamic Modelingmentioning

confidence: 99%

A Geophysical Perspective on the Bulk Composition of Mars

et al. 2018

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We invert the Martian tidal response and mean mass and moment of inertia for chemical composition, thermal state, and interior structure. The inversion combines phase equilibrium computations with a laboratory‐based viscoelastic dissipation model. The rheological model, which is based on measurements of anhydrous and melt‐free olivine, is both temperature and grain size sensitive and imposes strong constraints on interior structure. The bottom of the lithosphere, defined as the location where the conductive geotherm meets the mantle adiabat, occurs deep within the upper mantle (∼200–400 km depth) resulting in apparent upper mantle low‐velocity zones. Assuming an Fe‐FeS core, our results indicate (1) a mantle with a Mg# (molar Mg/Mg+Fe) of ∼0.75 in agreement with earlier geochemical estimates based on analysis of Martian meteorites; (2) absence of bridgmanite‐ and ferropericlase‐dominated basal layer; (3) core compositions (15–18.5 wt% S), core radii (1,730–1,840 km), and core‐mantle boundary temperatures (1620–1690°C) that, together with the eutectic‐like core compositions, suggest that the core is liquid; and (4) bulk Martian compositions with a Fe/Si (weight ratio) of 1.66–1.81. We show that the inversion results can be used in tandem with geodynamic simulations to identify plausible geodynamic scenarios and parameters. Specifically, we find that the inversion results are largely reproducible by stagnant lid convection models for a range of initial viscosities (∼1018–1020 Pa s) and radioactive element partitioning between crust and mantle around 0.01–0.1. The geodynamic models predict a mean surface heat flow between 15 and 25 mW/m2.

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Section: Geodynamic Modelingmentioning

confidence: 99%

A Geophysical Perspective on the Bulk Composition of Mars

et al. 2018

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“…The release of gravitational energy due to the progressive enrichment of the lighter element in the outer core will continue until the eutectic composition is reached. In this scenario, the energy E G ,released from a core that transitions from an initial compositionally uniform state with an average density

\overset{ρ}{true}

to a two‐layer core in its lowest gravitational potential energy configuration, is represented by the relation

E_{G} ((),, ρ_{1}, ρ_{2}) = \frac{16}{15} π^{2} G R_{c}^{5} ([], ρ_{1}^{2} - {\overset{true¯}{ρ}}^{2} + \frac{5}{2} ρ_{1} ((), \overset{ρ}{true} - ρ_{1}) + ((), \frac{3}{2} ρ_{1} - ρ_{2}) ((), ρ_{1} - ρ_{2}) {(\frac{\overset{ρ}{true} - ρ_{1}}{ρ_{2} - ρ_{1}})}^{\frac{5}{3}}),

where G is the gravitational constant, R c is the outer core radius, ρ 1 is the outer core density, and ρ 2 is the inner core density (see equations 2–4 in Breuer & Moore, ).…”

Section: Core Thermodynamicsmentioning

confidence: 99%

The Case Against an Early Lunar Dynamo Powered by Core Convection

Evans

Tikoo

Andrews-Hanna

2018

Geophysical Research Letters

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Paleomagnetic analyses of lunar samples indicate that the Moon had a dynamo‐generated magnetic field with ~50 μT surface field intensities between 3.85 and 3.56 Ga followed by a period of much lower (≤ ~5 μT) intensities that persisted beyond 2.5 Ga. However, we determine herein that there is insufficient energy associated with core convection—the process commonly recognized to generate long‐lived magnetic fields in planetary bodies—to sustain a lunar dynamo for the duration and intensities indicated. We find that a lunar surface field of ≤1.9 μT could have persisted until 200 Ma, but the ~50 μT paleointensities recorded by lunar samples between 3.85 and 3.56 Ga could not have been sustained by a convective dynamo for more than 28 Myr. Thus, for a continuously operating, convective dynamo to be consistent with the early lunar paleomagnetic record, either an exotic mechanism or unknown energy source must be primarily responsible for the ancient lunar magnetic field.

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“…In addition to transporting heat, volcanism is an important mass transport process, causing the surface temperature to be advected downward as old, cool flows are buried by newer flows. In the heat pipe regime, this profoundly affects the structure of the lithosphere, producing a thick, cold lid [ O'Reilly and Davies , ; Breuer and Moore , ; Moore and Webb , ]. By removing heat and thus buoyancy from the active boundary layer beneath the lid, heat pipes also reduce the stresses on the lid, suppressing plate tectonics [ Moore and Webb , ].…”

Section: Heat Transport Regimesmentioning

confidence: 99%

The efficiency of plate tectonics and nonequilibrium dynamical evolution of planetary mantles

Moore

Lenardic

2015

Geophysical Research Letters

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Consideration of the structure of dynamical equilibria in terrestrial planets using simplified descriptions of the relevant heat transport processes (rigid‐lid convection, plate tectonics, and heat pipe volcanism) reveals that if the efficiency of plate tectonic heat transport decreases at higher mantle temperature, then it cannot govern quasi‐equilibrium dynamical evolution, and the system is always evolving away from the plate tectonic regime. A planet on which plate tectonics is less efficient at higher temperature stays in heat pipe mode longer, spends less time undergoing plate tectonics, and has a low and ever‐decreasing Urey number during this phase. These conclusions are based solely on the structure of the equilibria in a system with less efficient plate tectonics in the past and are independent of the mechanisms leading to this behavior. Commonly used quasi‐equilibrium approaches to planetary thermal evolution are likely not valid for planets in which heat transport becomes less efficient at higher temperature.

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Dynamics and Thermal History of the Terrestrial Planets, the Moon, and Io

Cited by 69 publications

References 479 publications

A Geophysical Perspective on the Bulk Composition of Mars

A Geophysical Perspective on the Bulk Composition of Mars

The Case Against an Early Lunar Dynamo Powered by Core Convection

The efficiency of plate tectonics and nonequilibrium dynamical evolution of planetary mantles

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