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Top-down freezing in a Fe-FeS core and Ganymede's present-day magnetic field

Rückriemen, T. and Breuer, D. and Spohn, T. (2018) Top-down freezing in a Fe-FeS core and Ganymede's present-day magnetic field. Icarus: International Journal of Solar System Studies, 307, pp. 172-196. Elsevier. DOI: 10.1016/j.icarus.2018.02.021 ISSN 0019-1035

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Official URL: https://www.sciencedirect.com/science/article/abs/pii/S0019103517307029


Ganymede’s core most likely possesses an active dynamo today, which produces a magnetic field at the surface of  ∼ 719 nT. Thermochemical convection triggered by cooling of the core is a feasible power source for the dynamo. Experiments of different research groups indicate low pressure gradients of the melting temperatures for Fe–FeS core alloys at pressures prevailing in Ganymede’s core ( < 10 GPa). This may entail that the core crystallizes from the top instead of from the bottom as is expected for Earth’s core. Depending on the core sulfur concentration being more iron- or more sulfur-rich than the eutectic concentration either snowing iron crystals or a solid FeS layer can form at the top of the core. We investigate whether these two core crystallization scenarios are capable of explaining Ganymede’s present magnetic activity. To do so, we set up a parametrized one-dimensional thermal evolution model. We explore a wide range of parameters by running a large set of Monte Carlo simulations. Both freezing scenarios can explain Ganymede’s present-day magnetic field. Dynamos of iron snow models are rather young ( < 1 Gyr), whereas dynamos below the FeS layer can be both young and much older ( ∼ 3.8 Gyr). Successful models preferably contain less radiogenic heat sources in the mantle than the chondritic abundance and show a correlation between the reference viscosity in the mantle and the initial core sulfur concentration.

Item URL in elib:https://elib.dlr.de/125105/
Document Type:Article
Title:Top-down freezing in a Fe-FeS core and Ganymede's present-day magnetic field
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Rückriemen, T.Tina.Rueckriemen (at) dlr.deUNSPECIFIED
Breuer, D.doris.breuer (at) dlr.deUNSPECIFIED
Spohn, T.tilman.spohn (at) dlr.deUNSPECIFIED
Date:June 2018
Journal or Publication Title:Icarus: International Journal of Solar System Studies
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1016/j.icarus.2018.02.021
Page Range:pp. 172-196
Keywords:Ganymede, magnetic field, thermo-chemical evolution, Fe–FeS, core differentiation, top-down core crystallization
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Vorhaben Exploration des Sonnensystems
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research
Institute of Planetary Research > Planetary Physics
Deposited By: Rückriemen, Tina
Deposited On:17 Dec 2018 08:54
Last Modified:17 Dec 2018 08:54

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