Chondrites as samples of differentiated planetesimals

Elkins-Tanton, Linda T.; Weiss, B. P.; Zuber, M. T.

doi:10.1016/j.epsl.2011.03.010

Cited by 267 publications

(257 citation statements)

References 47 publications

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“…In contrast to the assumption of Hevey & Sanders (2006) that the parent bodies of differentiated meteorites formed prior to the accretion of the most chondritic parent bodies, our results indicate that both chondritic meteorites and differentiated meteorites can originate from one and the same parent body. This finding is consistent to the results of Weiss et al (2010) and Elkins-Tanton et al (2011), where a differentiated interior is covered with undifferentiated crust to explain the remanent magnetisation of the CV meteorite Allende.…”

Section: Summary and Discussionsupporting

confidence: 82%

“…In the model by Moskovitz & Gaidos (2011) -as before in the model by Sahijpal et al (2007) -it is assumed that silicate melt can rise toward the surface by porous flow and form a basaltic crust. An assumption that differs from another recent model by Elkins-Tanton et al (2011), who argue that silicate melt would not be able to reach the surface because of its higher density in comparison to that of the primordial crust. In their model, any melt that rises towards the surface would cool and crystallize as crust intrusions.…”

Section: Introductioncontrasting

confidence: 42%

“…Silicate melt is not able to reach the surface via porous flow as the melt freezes on its way to the surface, consistent to Elkins-Tanton et al (2011) who argue that buoyancy alone does not suffice to cause silicate eruption in small bodies with cool crusts. The migration velocities obtained in our model calculation are not high enough to prevent freezing in the narrow interconnected pores.…”

Section: Summary and Discussionmentioning

confidence: 57%

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Differentiation and core formation in accreting planetesimals

Neumann

Breuer

Spohn

2012

A&A

110

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Aims. The compositions of meteorites and the morphologies of asteroid surfaces provide strong evidence that partial melting and differentiation were widespread among the planetesimals of the early solar system. However, it is not easily understood how planetesimals can be differentiated. To account for significantly smaller radii, masses, gravity and accretion energies early, intense heat sources are required, e.g. the short-lived nuclides 26 Al and 60 Fe. Here, we investigate the process of differentiation and core formation in accreting planetesimals taking into account the effects of sintering, melt heat transport via porous flow and redistribution of the radiogenic heat sources. Methods. We use a spherically symmetric one-dimensional model of a partially molten planetesimal consisting of iron and silicates, which considers the accretion by radial growth. The common heat conduction equation has been modified to consider also melt segregation. In the initial state, the planetesimals are assumed to be highly porous and consist of a mixture of Fe,Ni-FeS and silicates consistent to an H-chondritic composition. The porosity change due to the so called hot pressing is simulated by solving a corresponding differential equation. Magma segregation of iron and silicate melt is treated according to the flow in porous media theory by using the Darcy flow equation and allowing a maximal melt fraction of 50%. Results. We show that the differentiation in planetesimals depends strongly on the formation time, accretion duration, and accretion law and cannot be assumed as instantaneous. Iron melt segregation starts almost simultaneously with silicate segregation and lasts between 0.4 and 10 Ma. The degree of differentiation varies significantly and the most evolved structure consists of an iron core, a silicate mantle, which are covered by an undifferentiated but sintered layer and an undifferentiated and unsintered regolith -suggesting that chondrites and achondrites can originate from the same parent body.

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Section: Summary and Discussionsupporting

confidence: 82%

Section: Introductioncontrasting

confidence: 42%

Section: Summary and Discussionmentioning

confidence: 57%

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Differentiation and core formation in accreting planetesimals

Neumann

Breuer

Spohn

2012

A&A

110

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“…Convection on these bodies is currently thought to have been thermally driven 7,8 , implying that magnetic activity would have been short-lived 9 . Here we present a time-series paleomagnetic record of the field recorded by the Imilac and Esquel pallasite meteorites, derived from nanomagnetic images 10 of their metallic matrices.…”

mentioning

confidence: 99%

“…Despite these caveats, the field intensity trends inferred from the CZ of the pallasites agree with our model predictions. The thermally driven dynamo activity that is widely believed to have acted on small bodies 7-9 is inefficient 15 (hence was likely uncommon) and could only have generated fields for the first 10 -50 million years (depending on the body's radius) after CAI formation 7,29 . Our results suggest that compositionally driven dynamo activity was generated in outwardly solidifying small body cores from ~60 -250 million after CAI formation, and lasted for the majority of core solidification (a further ~25 -150 million years depending on the body's radius) 1 .…”

mentioning

confidence: 99%

Long-lived magnetism from solidification-driven convection on the pallasite parent body

Bryson

Nichols

Herrero‐Albillos

et al. 2015

Nature

151

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Paleomagnetic measurements of meteorites 1-5 suggest that, shortly after the birth of the solar system, the molten metallic cores of many small planetary bodies convected vigorously and were capable of generating magnetic fields 6 . Convection on these bodies is currently thought to have been thermally driven 7,8 , implying that magnetic activity would have been short-lived 9 . Here we present a time-series paleomagnetic record of the field recorded by the Imilac and Esquel pallasite meteorites, derived from nanomagnetic images 10 of their metallic matrices. The results reveal a history of long-lived magnetic activity on the pallasite parent body, capturing the decay and eventual shut down of the magnetic field. We demonstrate that magnetic activity driven by progressive solidification of an inner core 11-13 is consistent with our measured magnetic field characteristics and cooling rates 14 . Solidification-driven convection was likely common among small body cores 15 , and, in contrast to thermally driven convection, will have led to a relatively late (hundreds of millions of years after accretion), long-lasting, intense and widespread epoch of magnetic activity among these bodies in the early solar system.The pallasites are slowly cooled (2 -9 K Myr -1 ) 14 stony-iron meteorites 16 , which originated from the mid-to upper-mantle of a ~200-km-radius body 1 . The slow cooling rate of these meteorites allowed for characteristic microstructures to form in their metal matrix 17 , a key feature of which are regions of intergrown nanoscale islands of tetrataenite (ordered FeNi) 18,19 and an ordered Fe 3 Ni matrix 20 , collectively known as cloudy zones (CZ) 21 . During parent body cooling, these tetrataenite islands exsolved and subsequently coarsened over tens of millions of years 22 . The island diameter decreases systematically across the CZ, reflecting a decrease in the local formation age of the islands 20 . Each island adopted one of three orthogonal magnetic easy axes as it formed 18,23 , thus could display any one of six magnetisation directions. Variations in the intensity and direction of an external magnetic field led to measurable differences in the populations of each magnetisation direction 20 . Crucially, the temporal evolution of an external field is recorded by the variations in the relative proportions of these directions across the CZ 10 , which can be quantified using high-resolution nanomagnetic imaging. These images were captured for the Imilac and Esquel pallasites, utilising X-ray magnetic circular dichroism 24,25 at the X-ray photoemission electron microscope (XPEEM) 26 at the BESSY II synchrotron, Berlin, which provides the spatially resolved magnetisation of a sample surface with a resolution down to 40 nm over a 5 µm field-of-view 10 .Four and six non-overlapping, 450-nm-wide regions across the CZ (decreasing age) were extracted from the XPEEM images of Imilac and Esquel meteorites, respectively (Fig. 1). The field recorded by each region was deduced by comparing the experimental XPEEM sig...

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Core solidification and dynamo evolution in a mantle‐stripped planetesimal

et al. 2016

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The physical processes active during the crystallization of a low-pressure, low-gravity planetesimal core are poorly understood but have implications for asteroidal magnetic fields and large-scale asteroidal structure. We consider a core with only a thin silicate shell, which could be analogous to some M-type asteroids including Psyche, and use a parameterized thermal model to predict a solidification timeline and the resulting chemical profile upon complete solidification. We then explore the potential strength and longevity of a dynamo in the planetesimal's early history. We find that cumulate inner core solidification would be capable of sustaining a dynamo during solidification, but less power would be available for a dynamo in an inward dendritic solidification scenario. We also model and suggest limits on crystal settling and compaction of a possible cumulate inner core.Iron meteorites can also provide information on the cooling rate experienced after solidification. Yang et al. [2008] examined several irons in the IVA meteorite family and found a large range of cooling rates within Key Points: • The rate and structure of inward fractional crystallization are constrained • Crystal settling could form a cumulate inner core with significant trapped melt • Constraints are placed on dynamo strength and longevity during solidification

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Chondrites as samples of differentiated planetesimals

Cited by 267 publications

References 47 publications

Differentiation and core formation in accreting planetesimals

Differentiation and core formation in accreting planetesimals

Long-lived magnetism from solidification-driven convection on the pallasite parent body

Core solidification and dynamo evolution in a mantle‐stripped planetesimal

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