W. Luecke¹, A. Kontny² and U. Kramar¹

¹Institut für Mineralogie und Geochemie, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany
²Institut für Angewandte Geowissenschaften, Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany

We combined high-resolution and space-resolved elemental distribution with investigations of magnetic minerals across Fe,Ni-alloy and troilite interfaces for two nonmagmatic (Morasko and Mundrabilla) IAB group iron meteorites and an octahedrite found in 1993 in Coahuila/Mexico (Coahuila II) preliminarily classified on Ir and Au content as IIAB group. The aim of this study was to elucidate the crystallization and thermal history using gradients of the siderophile elements Ni, Co, Ge, and Ga and the chalcophile elements Cr, Cu, and Se with a focus on magnetic minerals. The Morasko and Coahuila II meteorite show a several mm-thick carbon- and phosphorous-rich transition zone between Fe,Ni-alloy and troilite, which is characterized by magnetic cohenite and nonmagnetic or magnetic schreibersite. At Morasko, these phases have a characteristic trace element composition with Mo enriched in cohenite. In both Morasko and Coahuila II, Ni is enriched in schreibersite. The minerals have crystallized from immiscible melts, either by fractional crystallization and C- and P-enrichment in the melt, or by partial melting at temperatures slightly above the eutectic point. During crystallization of Mundrabilla, the field of immiscibility was not reached. Independent of meteorite group and cooling history, the magnetic mineralogy (daubreelite, cohenite and/or schreibersite, magnetite) is very similar to the troilite (and transition zone) for all three investigated iron meteorites. If these minerals can be separated from the metal, they might provide important information about the early solar system magnetic field. Magnetite is interpreted as a partial melting or a terrestrial weathering product of the Fe,Ni-alloy under oxidizing conditions.

Reference
Luecke W, Kontny A and Kramar U (in press) Geochemical zoning and magnetic mineralogy at Fe,Ni-alloy–troilite interfaces of three iron meteorites from Morasko, Coahuila II, and Mundrabilla. Meteoritics & Planetary Science
[doi:10.1111/maps.12288]
Published by arrangement with John Wiley & Sons

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Julien Faure¹, Sébastien Fromang¹ and Henrik Latter²

¹Laboratoire AIM, CEA/DSM – CNRS – Université Paris 7, Irfu/Service d’Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette, France
²Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, UK

Context. In protoplanetary disks, the inner boundary between the turbulent and laminar regions could be a promising site for planet formation, thanks to the trapping of solids at the boundary itself or in vortices generated by the Rossby wave instability. At the interface, the disk thermodynamics and the turbulent dynamics are entwined because of the importance of turbulent dissipation and thermal ionization. Numerical models of the boundary, however, have neglected the thermodynamics, and thus miss a part of the physics.
Aims. The aim of this paper is to numerically investigate the interplay between thermodynamics and dynamics in the inner regions of protoplanetary disks by properly accounting for turbulent heating and the dependence of the resistivity on the local temperature.
Methods. Using the Godunov code RAMSES, we performed a series of 3D global numerical simulations of protoplanetary disks in the cylindrical limit, including turbulent heating and a simple prescription for radiative cooling.
Results. We find that waves excited by the turbulence significantly heat the dead zone, and we subsequently provide a simple theoretical framework for estimating the wave heating and consequent temperature profile. In addition, our simulations reveal that the dead-zone inner edge can propagate outward into the dead zone, before stalling at a critical radius that can be estimated from a mean-field model. The engine driving the propagation is in fact density wave heating close to the interface. A pressure maximum appears at the interface in all simulations, and we note the emergence of the Rossby wave instability in simulations with extended azimuth.
Conclusions. Our simulations illustrate the complex interplay between thermodynamics and turbulent dynamics in the inner regions of protoplanetary disks. They also reveal how important activity at the dead-zone interface can be for the dead-zone thermodynamic structure.

Reference
Faure J, Fromang S and Latter H (2014) Thermodynamics of the dead-zone inner edge in protoplanetary disks. Astronomy & Astrophysics 564:A22.
[doi:10.1051/0004-6361/201321911]
Reproduced with permission © ESO

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Yuri I. Fujii¹, Satoshi Okuzumi^1,2, Takayuki Tanigawa³ and Shu-ichiro Inutsuka¹

¹Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8602, Japan
²Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
³Institute of Low Temperature Science, Hokkaido University, Sapporo 066-0819, Japan

We examine whether the magnetorotational instability (MRI) can serve as a mechanism of angular momentum transport in circumplanetary disks. For the MRI to operate the ionization degree must be sufficiently high and the magnetic pressure must be sufficiently lower than the gas pressure. We calculate the spatial distribution of the ionization degree and search for the MRI-active region where the two criteria are met. We find that there can be thin active layers at the disk surface depending on the model parameters, however, we find hardly any region which can sustain well-developed MRI turbulence; when the magnetic field is enhanced by MRI turbulence at the disk surface layer, a magnetically dominated atmosphere encroaches on a lower altitude and a region of well-developed MRI turbulence becomes smaller. We conclude that if there are no angular momentum transfer mechanisms other than MRI in gravitationally stable circumplanetary disks, gas is likely to pile up until disks become gravitationally unstable, and massive disks may survive for a long time.

Reference
Fujii YI, Okuzumi S, Tanigawa T and Shu-ichiro Inutsuka S-I (2014) On the Viability of the Magnetorotational Instability in Circumplanetary Disks. The Astrophysical Journal 785:101.
[doi:10.1088/0004-637X/785/2/101]

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