¹Claire C.Zurkowski,^2,3Barbara Lavina,¹Abigail Case,¹Kellie Swadba,²Stella Chariton,^1,2Vitali Prakapenk,¹Andrew J.Campbell
Earth and Planetary Science Letters 593, 117650 Link to Article [https://doi.org/10.1016/j.epsl.2022.117650]
¹University of Chicago, Department of the Geophysical Sciences, 5734 S Ellis Ave, Chicago, IL 60637, USA
²Center for Advanced Radiation Sources, The University of Chicago, Chicago, IL 60439, USA
³Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA
Copyright Elsevier

Cosmochemical considerations suggest that sulfur is a candidate light alloying element in rocky planetary cores, such that the high pressure-temperature (P-T) Fe-S phase relations likely play a key role in planetary core crystallization thermodynamics. The iron-saturated Fe-S phase relations were investigated to 200 GPa and 3250 K using combined powder and single-crystal X-ray diffraction techniques in a laser-heated diamond anvil cell. Upon heating at 120 GPa, I-4 Fe3S is observed to break down to form iron and a novel hexagonal Fe5S2 sulfide with the Ni5As2 structure (P6, ). To 200 GPa, Fe5S2 and Fe are observed to coexist at high temperatures while Fe2S polymorphs are identified with Fe at lower temperatures. An updated Fe-rich Fe-S phase diagram is presented. As this hexagonal Fe5S2 expresses complex Fe-Fe coordination and atomic positional disorder, crystallization of Fe5S2 may contribute to intricate elastic and electrical properties in Earth and planetary cores as they crystallize over time. Models of a fully crystallized Fe-rich Fe-S liquid in Earth’s and Venus’ core establish that Fe5S2 is likely the only sulfide to crystallize and may deposit in the outer third of the planets’ cores as they cool. Fe5S2 could further serve as a host for Ni and Si as has been observed in the related meteoritic phase perryite, (Fe, Ni)8(P, Si)3, adding intricacies to elemental partitioning during core crystallization. The stability of Fe5S2 presented here is key to understanding the role of sulfur in the crystallization sequences that drive the geodynamics and dictate the structures of Earth and rocky planetary cores.

¹A. Schmalen,¹R. Luther,^1,2,3N. Artemieva
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13832]
¹Museum für Naturkunde Berlin, Leibniz Institute for Evolution and Biodiversity Science, Berlin, 10115 Germany
²Planetary Science Institute, Tucson, Arizona, 85719 USA
³Institute for Dynamics of Geospheres, Russian Academy of Sciences, Moscow, 117049 Russia
Published by arrangement with John Wiley & Sons

This paper presents an attempt to reconstruct the Campo del Cielo (CdC) impact event, that is, to estimate the preatmospheric mass and velocity of the iron meteoroid and pre-impact parameters of its fragments allowing formation of funnels and impact craters. The goal of this study is to improve the understanding of the effects small-scale iron meteoroids can have on the Earth’s surface. We model the meteoroid’s atmospheric flight taking deceleration, ablation, and fragmentation into account, and then compare the results with available observations. We found that a fragment’s velocity near the surface should be <1 km s−1 in order to form a funnel with an intact meteorite inside. The estimates of preatmospheric (at an altitude of 100 km) parameters of the CdC impact event are as follows: minimal mass of 7500–8500 t, which corresponds to a diameter range of 12.2–12.8 m; maximum entry angle above the atmosphere of ~16.5° and velocities of 14.5–18.4  km s−1, which is close to the one most frequently reached by near-Earth objects (NEOs). Near the surface, the largest fragments with a mass of 400–1500 t and velocities of 4–7 km s−1 form impact craters whereas fragments with a mass <31 t and velocities <1 km s−1 form funnels. Masses <3 t are not included in our simulations. Their total mass is 280–460 t at the point of disruption but <110 t on the Earth’s surface. These numerous small fragments are dispersed over a large area and are very popular among meteorite hunters and dealers. In spite of all the observed crater location/size data and impactor velocity limits from the models, there are far more free parameters than constraints. As a result, any values for preatmospheric mass, velocity, and entry angle are merely representative or limitative as opposed to true values.