^1,2Laura Schaefer, ³Stein B. Jacobsen, ³John L. Remo, ^1,3M. I. Petaev, ¹Dimitar D. Sasselov
The Astrophysical Journal 835, 234 Link to Article [https://doi.org/10.3847/1538-4357/835/2/234]
¹Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
²Arizona State University, School of Earth and Space Exploration, Tempe, AZ 85287, USA
³Harvard University, Department of Earth and Planetary Sciences, 20 Oxford St., Cambridge, MA 02138, USA

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.

¹Carles E. Moyano-Cambero, ²Eva Pellicer, ¹Josep M. Trigo-Rodríguez, ³Iwan P. Williams, ⁴Jürgen Blum, ⁵Patrick Michel, ⁶Michael Küppers, ¹Marina Martínez-Jiménez, ¹Ivan Lloro, ⁷Jordi Sort
The Astrophysical Journal 835, 2 Link to Article [https://doi.org/10.3847/1538-4357/835/2/157]
¹Institute of Space Sciences (IEEC-CSIC), Meteorites, Minor Bodies and Planetary Sciences Group, Campus UAB Bellaterra, c/Can Magrans s/n, 08193 Cerdanyola del Vallès (Barcelona), Spain
²Departament de Física, Universitat Autónoma de Barcelona, E-08193 Bellaterra, Spain
³School of Physics and Astronomy, Queen Mary, University of London, 317 Mile End Road, E1 4NS London, UK
⁴Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, Mendelssohnstr. 3, D-38106 Braunschweig, Germany
⁵Lagrange Laboratory, University of Nice, CNRS, Côte d’Azur Observatory, France
⁶European Space Agency, European Space Astronomy Centre, P.O. Box 78, Villanueva de la Cañada E-28691, Spain
⁷Institució Catalana de Recerca i Estudis Avançats (ICREA) and Departament de Física, Universitat Autónoma de Barcelona, E-08193 Bellaterra, Spain

The Chelyabinsk meteorite is a highly shocked, low porosity, ordinary chondrite, probably similar to S- or Q-type asteroids. Therefore, nanoindentation experiments on this meteorite allow us to obtain key data to understand the physical properties of near-Earth asteroids. Tests at different length scales provide information about the local mechanical properties of the minerals forming this meteorite: reduced Young’s modulus, hardness, elastic recovery, and fracture toughness. Those tests are also useful to understand the potential to deflect threatening asteroids using a kinetic projectile. We found that the differences in mechanical properties between regions of the meteorite, which increase or reduce the efficiency of impacts, are not a result of compositional differences. A low mean particle size, attributed to repetitive shock, can increase hardness, while low porosity promotes a higher momentum multiplication. Momentum multiplication is the ratio between the change in momentum of a target due to an impact, and the momentum of the projectile, and therefore, higher values imply more efficient impacts. In the Chelyabinsk meteorite, the properties of the light-colored lithology materials facilitate obtaining higher momentum multiplication values, compared to the other regions described for this meteorite. Also, we found a low value of fracture toughness in the shock-melt veins of Chelyabinsk, which would promote the ejection of material after an impact and therefore increase the momentum multiplication. These results are relevant to the growing interest in missions to test asteroid deflection, such as the recent collaboration between the European Space Agency and NASA, known as the Asteroid Impact and Deflection Assessment mission.