A dynamo model with double diffusive convection for Mercury's core

Manglik, A.; Wicht, Johannes; Christensen, Ulrich R.

doi:10.1016/j.epsl.2009.12.007

Cited by 80 publications

(102 citation statements)

References 34 publications

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“…Apart from neglecting double-diffusive convection, this approach fails to accurately prescribe the inner boundary condition. Some models have already incorporated thermal and chemical convection with appropriate boundary conditions in numerical dynamos (Manglik et al 2010;Takahashi 2014;Trümper et al 2012). Tracer methods which are commonly used in mantle convection simulations (e.g., Tackley and King 2003) may be applied to chemical convection in dynamo codes for more accurate numerical schemes.…”

Section: Future Prospectsmentioning

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: Future Prospectsmentioning

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.

View full text Add to dashboard Cite

show abstract

“…The field is then strongly attenuated by the electromagnetic skin effect of the stagnant (i.e., no vertical movement) but electrically conducting layer. However, the stagnant layer may be destabilized by double diffusive effects, which can only be avoided if the sulfur concentration in Mercury's core is very small, only a fraction of a percent (Manglik et al 2010). A core with such a low sulfur concentration is again not likely to be consistent with the geodetic and tectonic evidence (Hauck et al 2004;Grott et al 2011;Tosi et al 2013).…”

Section: Mercurymentioning

confidence: 94%

Iron snow, crystal floats, and inner-core growth: modes of core solidification and implications for dynamos in terrestrial planets and moons

Breuer

Rueckriemen

Spohn

2015

Prog. in Earth and Planet. Sci.

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Recent planetary space missions, new experimental data, and advanced numerical techniques have helped to improve our understanding of the deep interiors of the terrestrial planets and moons. In the present review, we summarize recent insights into the state and composition of their iron (Fe)-rich cores, as well as recent findings about the magnetic field evolution of Mercury, the Moon, Mars, and Ganymede. Crystallizing processes in iron-rich cores that differ from the classical Earth case (i.e., Fe snow and iron sulfide (FeS) crystallization) have been identified and found to be important in the cores of terrestrial bodies. The Fe snow regime occurs at pressures lower than that in the Earth's core on the iron-rich side of the eutectic, where iron freezes first close to the core-mantle boundary rather than in the center. FeS crystallization, instead, occurs on the sulfur-rich side of the eutectic. Depending on the core temperature profile and the pressure range considered, FeS crystallizes either in the core center or close to the core-mantle boundary. The consequences of the various crystallizing mechanisms for core dynamics and magnetic field generation are discussed. For the Moon, revised paleomagnetic data obtained with advanced techniques suggest a peculiar history of its internal dynamo, with an early strong field persisting between 4.25 and 3.5 Ga, and subsequently a much weaker field. In addition, the long-lasting dynamo and the possible presence of an inner core, as inferred from a revised interpretation of Apollo seismic data, suggest core crystallization as a viable process of magnetic field generation for a substantial period during lunar evolution. The present-day magnetic fields of Mercury and Ganymede (if they occur on the iron-rich side of the Fe-FeS eutectic) and the related dynamo action are likely generated in the Fe snow regime and seem to be recent features. An earlier dynamo in Mercury would have been powered differently. For Mercury, MESSENGER data further suggest core formation under reducing conditions that may have resulted in an Fe-S-Si composition, further complicating the core crystallization process. Mars, with its early and strong paleo-field, likely has not yet started to freeze out an inner iron core.

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“…Thin-shell dynamos (Stanley et al, 2005;Takahashi and Matsushima, 2006); thickshell dynamos (Heimpel et al, 2005); deep dynamos operating below a stably stratified, electrically conducting layer (Christensen, 2006;Christensen and Wicht, 2006;Manglik et al, 2010;Wicht et al, 2007); dynamos with induction feedback from magnetopause currents (Glassmeier et al, 2007a,b;Gó mex-Pérez and Solomon, 2010;Gó mex-Pérez and Wicht, 2010;Heyner et al, 2011a,b); and dynamos driven by precipitation of solid iron (Vilim et al, 2010) all can produce a weak field. However, thin-shell dynamos show a dipole offset much less than observed at Mercury or no quadrupole dominance over higher multipoles (Stanley et al, 2005).…”

Section: Magnetic Fieldmentioning

confidence: 96%

“…In addition, zonal flows set up in the stably stratified layer preferentially reduce nonaxisymmetric, low-degree terms (Christensen and Wicht, 2006), yielding a surface field that is weak, dipole-dominant with a substantial quadrupole component, and axisymmetric. The field structure produced by these models is highly dependent on the thickness of the stable layer and its dynamics (Manglik et al, 2010;Stanley and Mohammadi, 2008). It is not yet clear that we understand the processes behind the generation of Mercury's unusual magnetic field.…”

Section: Magnetic Fieldmentioning

confidence: 99%