Differentiation and core formation in accreting planetesimals

Neumann, Wladimir; Breuer, D.; Spohn, Tilman

doi:10.1051/0004-6361/201219157

Cited by 82 publications

(115 citation statements)

References 69 publications

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“…For the details of the model we refer to some of our previous publications, Neumann et al (2012Neumann et al ( , 2014b. In the following, we describe the details of the model that are particularly crucial and specific here.…”

Section: Modelmentioning

confidence: 99%

“…in Neumann et al (2012). For the derivation of the associated differential equation see Kortenkamp et al (2000).…”

Section: Modelmentioning

confidence: 99%

“…Alternatively, water vapour available for reactions in the primitive solar nebula could have led to direct condensation of hydrous minerals. In Neumann et al (2012Neumann et al ( , 2014b we used an activation energy of 356 kJ mol −1 (85 kcal mol −1 ) calculated by Schwenn & Goetze (1978) for olivine. Compaction took place in this model at a temperature of about 700 K. On the other hand, a creep activation energy of 356 kJ mol −1 is rather high for a carbonaceous chondritic composition, which is dominated by phyllosilicates / serpentine.…”

Section: Modelmentioning

confidence: 99%

“…Additional model runs performed using a linear and asymptotic accretion law (see Neumann et al 2012) instead of an exponential law (Eq. (2)) confirm our results.…”

Section: Prolonged Accretion and Different Accretion Behaviourmentioning

confidence: 99%

“…To do this, we extended the numerical code from Neumann et al (2012), which computes the thermal and structural evolution of planetesimals including compaction of the initially porous primordial material (modelled using a creep law) and the coupling of this process with a continuous accretion. In particular, we investigate the evolution of the interior assuming an initially porous structure.…”

Section: Introductionmentioning

confidence: 99%

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Modelling the internal structure of Ceres: Coupling of accretion with compaction by creep and implications for the water-rock differentiation

Neumann

Breuer

Spohn

2015

A&A

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Aims. We model the compaction of a Ceres-like body that accretes from the protoplanetary dust as a porous aggregate. To do this, we use a comprehensive numerical model in which the accretion starts with a km-size seed and the final radius reaches ≈500 km. Our goal is to investigate the interplay of accretion and loss of porosity by hot pressing. We draw conclusions for the evolution of the porosity profile and the present-day porosity distribution on Ceres. In particular, we test the hypothesis that Ceres' low density can be explained by a porous interior instead of by the presence of ice, and whether compaction occurs due to creep or due to dehydration of hydrated minerals. Methods. We extended our thermal evolution model from previous studies to model compaction of an accreting asteroid that is initially porous. We considered two different compositions of Ceres suggested by other workers. The porosity change was calculated according to the thermally activated creep flow. Depending on the composition, parameters relevant for compaction were changed self-consistently with the mineral phases. Results. We find that compaction of initially porous Ceres is dominated by creep and only slightly perturbed by the dehydration. In particular, dehydration alone cannot lead to compaction because creep can occur before the dehydration. Depending on the accretion duration, timing of the compaction varies from between a few million years and more than one billion years. Thereby, late accretion cannot prevent compaction to an average porosity of <2.5%. We provide the evolution as well as the present-day porosity and temperature profiles for Ceres. The temperature allows for the existence of liquid water in the interior of Ceres at a depths of ≥5−33 km. Depending on the composition, either iron melt is produced regardless of the accretion timing or only for an accretion within the first 4 Ma relative to calcium-aluminium-rich inclusions. This argues for a small metallic core.

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Section: Modelmentioning

confidence: 99%

“…in Neumann et al (2012). For the derivation of the associated differential equation see Kortenkamp et al (2000).…”

Section: Modelmentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

“…Additional model runs performed using a linear and asymptotic accretion law (see Neumann et al 2012) instead of an exponential law (Eq. (2)) confirm our results.…”

Section: Prolonged Accretion and Different Accretion Behaviourmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modelling the internal structure of Ceres: Coupling of accretion with compaction by creep and implications for the water-rock differentiation

Neumann

Breuer

Spohn

2015

A&A

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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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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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Differentiation and core formation in accreting planetesimals

Cited by 82 publications

References 69 publications

Modelling the internal structure of Ceres: Coupling of accretion with compaction by creep and implications for the water-rock differentiation

Modelling the internal structure of Ceres: Coupling of accretion with compaction by creep and implications for the water-rock differentiation

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

Core solidification and dynamo evolution in a mantle‐stripped planetesimal

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