Metal-silicate Partitioning and Its Role in Core Formation and Composition on Super-Earths

Journal Article · Wed Feb 01 00:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/835/2/234· OSTI ID:22663909

Schaefer, Laura; Petaev, M. I.; Sasselov, Dimitar D. ^[1]; Jacobsen, Stein B.

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1. Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)

We use a thermodynamic framework for silicate-metal partitioning to determine the possible compositions of metallic cores on super-Earths. We compare results using literature values of the partition coefficients of Si and Ni, as well as new partition coefficients calculated using results from laser shock-induced melting of powdered metal-dunite targets at pressures up to 276 GPa, which approaches those found within the deep mantles of super-Earths. We find that larger planets may have little to no light elements in their cores because the Si partition coefficient decreases at high pressures. The planet mass at which this occurs will depend on the metal-silicate equilibration depth. We also extrapolate the equations of state (EOS) of FeO and FeSi alloys to high pressures, and present mass–radius diagrams using self-consistent planet compositions assuming equilibrated mantles and cores. We confirm the results of previous studies that the distribution of elements between mantle and core will not be detectable from mass and radius measurements alone. While observations may be insensitive to interior structure, further modeling is sensitive to compositionally dependent properties, such as mantle viscosity and core freeze-out properties. We therefore emphasize the need for additional high pressure measurements of partitioning as well as EOSs, and highlight the utility of the Sandia Z-facilities for this type of work.

• OSTI ID: 22663909
• Journal Information: Astrophysical Journal, Vol. 835, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COMPARATIVE EVALUATIONS
DISTRIBUTION
EQUATIONS OF STATE
FREEZING OUT
IRON OXIDES
IRON SILICIDES
MASS
MELTING
METALS
PARTITION
PLANETS
POWDERS
PRESSURE MEASUREMENT
PRESSURE RANGE GIGA PA
SATELLITES
SILICATES
SIMULATION
THERMODYNAMICS
VISCOSITY
VISIBLE RADIATION