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Differentiation and core formation in accreting planetesimals

Neumann, W. and Breuer, D. and Spohn, T. (2012) Differentiation and core formation in accreting planetesimals. Astronomy and Astrophysics, 543 (A141), pp. 1-21. DOI: 10.1051/0004-6361/201219157.

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Official URL: http://dx.doi.org/10.1051/0004-6361/201219157

Abstract

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 26Al and 60Fe. 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.

Document Type:Article
Title:Differentiation and core formation in accreting planetesimals
Authors:
AuthorsInstitution or Email of Authors
Neumann, W.wladimir.neumann@dlr.de
Breuer, D.doris.breuer@dlr.de
Spohn, T.Tilman.Spohn@dlr.de
Date:12 July 2012
Journal or Publication Title:Astronomy and Astrophysics
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:543
DOI:10.1051/0004-6361/201219157
Page Range:pp. 1-21
Series Name:Planets and planetary systems
Status:Published
Keywords:convection / planets and satellites: formation / planets and satellites: interiors / minor planets, asteroids: general / conduction
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Vorhaben Exploration des Sonnensystems (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Physics
Institute of Planetary Research
Deposited By: Lena Noack
Deposited On:19 Sep 2012 08:25
Last Modified:26 Mar 2013 13:41

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