Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites

Breuer, D.; Labrosse, S.; Spohn, Tilman

doi:10.1007/s11214-009-9587-5

Cited by 66 publications

(50 citation statements)

References 252 publications

(308 reference statements)

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“…Figure 16 shows the CMB heat flux patterns resulting from an impactor of 800 km radius falling on the north pole (left) or the equator (right) of Mars' surface. Because it is thought that there is no inner core in Mars (Breuer et al 2010;Schubert and Spohn 1990), purely thermal convection was modeled, with a volumetric homogeneous heat source that compensated for the loss of heat through the outer boundary (Amit et al 2011a;Dietrich and Wicht 2013). A small inner core corresponding to r i /r o = 0.2 was retained to avoid numerical instabilities, but the inner boundary was set to be convectively passive (Table 1).…”

Section: Localized Mantle Heating and The Paleo Dynamo Of Marsmentioning

confidence: 99%

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Amit

Choblet

Olson

et al. 2015

Prog. in Earth and Planet. Sci.

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Mantle control on planetary dynamos is often studied by imposing heterogeneous core-mantle boundary (CMB) heat flux patterns on the outer boundary of numerical dynamo simulations. These patterns typically enter two main categories: Either they are proportional to seismic tomography models of Earth's lowermost mantle to simulate realistic conditions, or they are represented by single spherical harmonics for fundamental physical understanding. However, in reality the dynamics in the lower mantle is much more complicated and these CMB heat flux models are most likely oversimplified. Here we term alternative any CMB heat flux pattern imposed on numerical dynamos that does not fall into these two categories, and instead attempts to account for additional complexity in the lower mantle. We review papers that attempted to explain various dynamo-related observations by imposing alternative CMB heat flux patterns on their dynamo models. For present-day Earth, the alternative patterns reflect non-thermal contributions to seismic anomalies or sharp features not resolved by global tomography models. Time-dependent mantle convection is invoked for capturing past conditions on Earth's CMB. For Mars, alternative patterns account for localized heating by a giant impact or a mantle plume. Recovered geodynamo-related observations include persistent morphological features of present-day core convection and the geomagnetic field as well as the variability in the geomagnetic reversal frequency over the past several hundred Myr. On Mars the models aim at explaining the demise of the paleodynamo or the hemispheric crustal magnetic dichotomy. We report the main results of these studies, discuss their geophysical implications, and speculate on some future prospects.

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Section: Localized Mantle Heating and The Paleo Dynamo Of Marsmentioning

confidence: 99%

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Amit

Choblet

Olson

et al. 2015

Prog. in Earth and Planet. Sci.

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“…Breuer et al (2010), summarizing earlier suggestions (Stevenson 1983), note that saturation of metal in light elements might occur at the lower pressures of a magma ocean that might later exsolve from the metal due to oversaturation at higher pressures after the metal segregates to form the core. Flow of exsolved material upwards in the core could drive a dynamo, which Hirose et al (2017) show that it is quite efficient and possibly operates the present-day Earth's.…”

Section: Introductionmentioning

confidence: 57%

“…It appears more difficult to do this with geostrophic flows ( ν CIA ) because the required heat flows are too large: 100-1000 times the present-day estimates. Convection models for the evolution of heat flow of Mars (Breuer et al 2010) show that heat flows high enough to run a magnetostrophic mantle dynamo existed between 0-1 Gyr after accretion ended, which would provide the required heat flow increase in the time frame for the dynamo's existence. It therefore seems possible that the earliest-surviving crust in the magma ocean phase of planetary evolution could record a magnetic field generated by a mantle dynamo, independent of whether a core dynamo was also operating.…”

Section: Resultsmentioning

confidence: 99%

“…This fluid motion is able to drive the dynamo quite efficiently and for a long time. For example, scaling laws for the growth of the Earth's inner core (Breuer et al 2010) suggest that it requires another 10-20 Gyr to crystallize the whole core and thus extinguish dynamo activity. This dynamo may be described as a compositional type because it is the changing composition of the crystallizing fluid that primarily contributes to its running.…”

Section: Introductionmentioning

confidence: 99%

“…This state must have been achieved by ∼500 Myr, which is about the limit age of magnetized areas of the Martian crust. Again, using the scaling laws for inner core growth (Breuer et al 2010), the growth time requires that the inner core nucleated quite early in Mars' accretion history; 100 year after core formation. Given that accretion times are on the order of 10 Myr (Brasser 2013), the scaling places the inner core's (and thus its magnetic field's) onset time before accretion's end and requires inner core growth during accretion and during growth of the core itself.…”

Section: Introductionmentioning

confidence: 99%

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Feasibility of a magma ocean dynamo on Mars

Helffrich

2017

Prog Earth Planet Sci

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Crustal magnetization of rocks in regions of Mars surface testifies to an era of dynamo activity. I examine the possibility that the dynamo that operated then, in the first 400-600 Ma after Mars formed, was powered by a crystallizing subsurface magma ocean. Of the ways that a magma ocean dynamo could operate, on Mars only turbulent and magnetostrophic dynamos seem feasible; geostrophic dynamos do not seem so unless very high heat flows, 100-1000 times present, are invoked. Given the anticipated information from the future InSight lander mission, it will be difficult to assess where the dynamo originated unless an inner core is discovered, rendering the dynamo likely to have operated in the core.

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Consequences of giant impacts in early Mars: Core merging and Martian dynamo evolution

Monteux

Arkani‐Hamed

2014

JGR Planets

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A giant impact is an increasingly popular explanation for the formation of the northern lowland on Mars. It is plausible that at the impact time both Mars and the impactor were differentiated with solid silicate mantles and liquid iron cores. Such a large impact likely resulted in merging of the cores of both bodies, a process which will have implications on the thermal state of the planet. We model the evolution of the Martian mantle following a giant impact and characterize the thermochemical consequences of the sinking of an impactor's core as a single diapir. The impact heating and the viscous heating induced during the core merging may affect the early thermal state of Mars during several tens of million years. Our results show that large viscosity contrasts between the impactor's core and the surrounding mantle silicates can reduce the duration of the merging down to 1 kyr but do not modify the merging temperature. When the viscosity contrast between the diapir and the surrounding silicates is larger than a factor of 1000, the descent of the diapir can lead to some entrainment of the relatively shallow silicates to deepest regions close to the core-mantle boundary. Finally, the direct impact heating of Martian core leads to thermal stratification of the core and kills the core dynamo. It takes on the order of 150-200 Myr to reinitiate a strong dynamo anew. The merging of the impactor's core with the Martian core only delays the reinitiation of the dynamo for a very short time.

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Thermal Evolution and Magnetic Field Generation in Terrestrial Planets and Satellites

Cited by 66 publications

References 252 publications

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Feasibility of a magma ocean dynamo on Mars

Consequences of giant impacts in early Mars: Core merging and Martian dynamo evolution

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