Leonardo Krapp¹, Oliver Gressel^1,2, Pablo Benítez-Llambay¹, Turlough P. Downes³, Gopakumar Mohandas^1,2, and Martin E. Pessah¹
Astrophysical Journal 865, 105 Link to Article [DOI: 10.3847/1538-4357/aadcf0]
¹Niels Bohr International Academy, The Niels Bohr Institute, Blegdamsvej 17, DK-2100, Copenhagen Ø, Denmark
²Kavli Institute for Theoretical Physics, University of California, Santa Barbara 93106, USA
³Centre for Astrophysics & Relativity, School of Mathematical Sciences, Dublin City University (DCU), Ireland

Imaging of the dust continuum emitted from disks around nearby protostars reveals diverse substructure. In recent years, theoretical efforts have been intensified to investigate how far the intrinsic dynamics of protoplanetary disks (PPDs) can lead to such features. Turbulence in the realm of non-ideal magnetohydrodynamics (MHD) is one candidate for explaining the generation of zonal flows which can lead to local dust enhancements. Adopting a radially varying cylindrical disk model, and considering combinations of vertical and azimuthal initial net flux, we perform 3D non-ideal MHD simulations aimed at studying self-organization induced by the Hall effect in turbulent PPDs. To this end, new modules have been incorporated into the Nirvana-iii and FARGO3D MHD codes. We moreover include dust grains, treated in the fluid approximation, in order to study their evolution subject to the emerging zonal flows. In the regime of a dominant Hall effect, we robustly obtain large-scale organized concentrations in the vertical magnetic field that remain stable for hundreds of orbits. For disks with vertical initial net flux alone, we confirm the presence of zonal flows and vortices that introduce regions of super-Keplerian gas flow. Including a moderately strong net-azimuthal magnetic flux can significantly alter the dynamics, partially preventing the self-organization of zonal flows. For plasma beta-parameters smaller than 50, large-scale, near-axisymmetric structures develop in the vertical magnetic flux. In all cases, we demonstrate that the emerging features are capable of accumulating dust grains for a range of Stokes numbers.

¹Maria Rosa Scicchitano,^1,2,3Daniela Rubatto, ^1,2Jörg Hermann, ⁴Alik S.Majumdar, ⁵Andrew Putnis
Chemical Geology 499, 126-137 Link to Article [https://doi.org/10.1016/j.chemgeo.2018.09.020]
¹Research School of Earth Sciences, Australian National University, Canberra 2601, ACT, Australia
²Institute of Geological Sciences, University of Bern, 3012 Bern, Switzerland
³Institute of Earth Sciences, University of Lausanne, Geopolis, 1015 Lausanne, Switzerland
⁴Geosciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, Gujarat, India
⁵The Institute for Geoscience Research, Curtin University, Perth 6845, WA, Australia

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Sanemichi Z. Takahashi^1,2 and Takayuki Muto³
Astrophysical Journal 865, 102 Link to Article [DOI: 10.3847/1538-4357/aadda0]
¹Department of Applied Physics, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677, Japan
²National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³Division of Liberal Arts, Kogakuin University, 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677, Japan

Structure formation in young protoplanetary disks is investigated using a one-dimensional model including the formation and the evolution of disks. Recent observations with ALMA found that a ring–hole structure may be formed in young protoplanetary disks, even when the disk is embedded in the envelope. We present a one-dimensional model for the formation of a protoplanetary disk from a molecular cloud core and its subsequent long-term evolution within a single framework. Such long-term evolution has not been explored by numerical simulations due to the limitations of computational power. In our model, we calculate the time evolution of the surface density of the gas and dust with the wind mass loss and the radial drift of the dust in the disk. We find that the MHD disk wind is a viable mechanism for the formation of a ring–hole structure in young disks. We perform a parameter study of our model and derive conditions for the formation of ring–hole structures within 6 × 10⁵ yr after the start of the collapse of the molecular cloud core. The final outcome of the disk shows five types of morphology; this can be understood by comparing the timescales of the viscous diffusion, the mass loss by MHD disk wind, and the radial drift of the dust. We discuss the implication of the model for the WL 17 system, which is suspected to be an embedded, yet transitional, disk.

¹Yu.Shkuratov, ¹Ye.Surkov, ²M.Ivanov, ¹V.Korokhin, ¹V.Kaydash, ³G.Videen, ⁴C.Pieters, ¹D.Stankevich
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.11.002]
¹V.N. Karazin Kharkiv National University, 35 Sumska St, Kharkiv, 61022, Ukraine
²V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 19, Kosygin st., 119991 Moscow, Russia
³Space Science Institute, 4750 Walnut St. Suite 205, Boulder CO 80301, USA
⁴Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA
Copyright Elsevier

We provide and test a method to obtain significant improvement of available Chandrayaan-1 M³ data. The advance is achieved using the Gaussian λ-convolution of spectra and Fourier filtration of images. The main result is imagery of the reflectance across different wavelengths as well as parameters of 1 μm and 2 μm absorption bands with unprecedented quality. This approach can be particularly useful for further investigations using M³ data, since it produces improved imagery of various lunar surface characteristics. We studied a region comprising a portion of the Aristarchus Plateau, Montes Agricola, and a small part of the mare surface in Ocean Procellarum to the north of Montes Agricola. We found that the lava flows in the area between the Aristarchus Plateau and Montes Agricola have a chemical/mineral composition different in comparison with mare areas to the northwest of the ridge Montes Agricola. We also identified distinct spectral properties of morphologically young craters located on the plateau and mare surface. A correlation diagram for positions of the minima of the 1 μm and 2 μm bands allows a cluster analysis of the region, and we map areas associated with a cluster corresponding to pyroclastic glasses. Relationships between geologic and spectral parameter maps were established.

¹Speelmanns, I.M., ¹Schmidt, M.W., ¹Liebske, C.
Geophysical Research Letters 45, 7434-7443 Link to Article [DOI: 10.1029/2018GL079130]
¹ETH Zurich, Department of Earth Sciences, Zurich ZH,, Switzerland

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Daiki Yamamoto¹, Minami Kuroda¹, Shogo Tachibana^1,2, Naoya Sakamoto³, and Hisayoshi Yurimoto^1,4
Astrophysical Journal 865, 98 Link to Article [DOI: 10.3847/1538-4357/aadcee]
¹Department of Natural History Sciences, Hokkaido University, Sapporo, Hokkaido 060-0810, Japan
²UTokyo Organization for Planetary Space Science, The University of Tokyo, Hongo, Tokyo 113-0033, Japan
³Isotopic Imaging Laboratory, Hokkaido University, Sapporo, 001-0021, Japan
⁴Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Kanagawa, 252-210, Japan

Meteoritic evidence suggests that oxygen isotopic exchange between ¹⁶O-rich amorphous silicate dust and ¹⁶O-poor water vapor occurred in the early solar system. In this study, we experimentally investigated the kinetics of oxygen isotopic exchange between submicron-sized amorphous forsterite grains and water vapor at protoplanetary disk-like low pressures of water vapor. The isotopic exchange reaction rate is controlled either by diffusive isotopic exchange in the amorphous structure or by the supply of water molecules from the vapor phase. The diffusive oxygen isotopic exchange occurred with a rate constant D (m² s⁻¹) = (1.5 ± 1.0) × 10⁻¹⁹ exp[−(161.5 ± 14.1 (kJ mol⁻¹))R⁻¹(1/T−1/1200)] at temperatures below ~800–900 K, and the supply of water molecules from the vapor phase could determine the rate of oxygen isotopic exchange at higher temperatures in the protosolar disk. On the other hand, the oxygen isotopic exchange rate dramatically decreases if the crystallization of amorphous forsterite precedes the oxygen isotopic exchange reaction with amorphous forsterite. According to the kinetics for oxygen isotopic exchange in protoplanetary disks, original isotopic compositions of amorphous forsterite dust could be preserved only if the dust was kept at temperatures below 500–600 K in the early solar system. The ¹⁶O-poor signatures for the most pristine silicate dust observed in cometary materials implies that the cometary silicate dust experienced oxygen isotopic exchange with ¹⁶O-poor water vapor through thermal annealing at temperatures higher than 500–600 K prior to their accretion into comets in the solar system.

Takuya Ojima¹, Yuhri Ishimaru¹, Shinya Wanajo^2,3, Nikos Prantzos⁴, and Patrik François^5,6
Astrophysical Journal 865, 87 Link to Article [DOI: 10.3847/1538-4357/aada11]
¹Department of Material Science, International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan
²Department of Engineering and Applied Sciences, Sophia University, Chiyoda-ku, Tokyo 102-8554, Japan
³iTHEMS Research Group, RIKEN, Wako, Saitama 351-0198, Japan
⁴Institut d’Astrophysique de Paris, UMR7095 CNRS, Univ. P. & M. Curie, 98bis Bd. Arago, F-75104 Paris, France
⁵GEPI, Observatoire de Paris, PSL Research University, CNRS, 61 Avenue de l’Observatoire, F-75014 Paris, France
⁶Université de Picardie Jules Verne, 33 rue St Leu, Amiens, France

Mergers of compact binaries (of a neutron star and another neutron star or a black hole, NSMs) are suggested to be the promising astrophysical site of the r-process. While the average coalescence timescale of NSMs appears to be , most of previous chemical evolution models indicate that the observed early appearance and large dispersion of in Galactic halo stars at favors shorter coalescence times of 1–10 Myr. We argue that this is not the case for the models assuming the formation of the Galactic halo from clustering of subhalos with different star formation histories as suggested by Ishimaru et al. We present a stochastic chemical evolution model of the subhalos, in which the site of the r-process is assumed to be mainly NSMs with a coalescence timescale of . In view of the scarcity of NSMs, their occurrence in each subhalo is computed with a Monte Carlo method. Our results show that the less massive subhalos evolve at lower metallicities and generate highly r-process-enhanced stars. An assembly of these subhalos leaves behind the large star-to-star scatters of in the Galactic halo as observed. However, the observed scatters of [Sr/Ba] at low metallicities indicate the presence of an additional site that partially contributes to the enrichment of light neutron-capture elements such as Sr. The high enhancements of at low metallicities found in our low-mass subhalo models also qualitatively reproduce the abundance signatures of the stars in the recently discovered ultra-faint dwarf galaxy Reticulum II. Therefore, our results suggest NSMs as the dominant sources of r-process elements in the Galactic halo.

¹Francis Nimmo²Katherine Kretke,³Shigeru Ida,⁴Soko Matsumura,⁵Thorsten Kleine
Space Science Reviews 214, 101 Link to Article [DOI
https://doi.org/10.1007/s11214-018-0533-2]
¹Dept. Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, USA
²South-west Research Institute, Boulder, USA
³Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan
⁴Dept. Physics, Dundee University, Dundee, UK
⁵Institut fur Planetologie, Universitat Muenster Münster, Germany

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^1,2,3L. Suárez-Andrés, ^1,2G. Israelian, ^1,2J. I. González Hernández, ⁴V. Zh. Adibekyan, ⁴E. Delgado Mena, ^4,5N. C. Santos, ^4,5S. G. Sousa
Astronomy & Astrophysics 614, A84 Link to Article [https://doi.org/10.1051/0004-6361/201730743]
¹Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
²Departmento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de la Palma, Spain
⁴Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁵Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal

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¹James M.D.May
American Mineralogist 103, 11 Link to Article [https://doi.org/10.2138/am-2018-6368]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0244, U.S.A.
Copyright: The Mineralogical Society of America

Low oxygen fugacity (fO2) in the lunar interior (one log unit below the iron-wüstite buffer [IW-1]) offers the possibility that stable Fe-metal and sulfide phases exist as restites within lunar mare basalt source regions. Metal and sulfide phases have high metal-melt and sulfide-melt partition coefficients for chalcophile, siderophile (>100), and highly siderophile elements (>>100 000; HSE: Os, Ir, Ru, Rh, Pt, Pd, Re, Au). If these phases are residual after mare basalt extraction, they would be expected to retain significant quantities of these elements, likely generating non-chondritic HSE inter-element ratios, including Re/Os in the silicate magma. If such phases were present, then the estimated HSE abundances of the bulk silicate moon (BSM) would be proportionally higher than current estimates (0.00023 ± 2 × CI chondrite), and perhaps closer to the bulk silicate earth (BSE) estimate (0.009 ± 2 × CI chondrite). Here I show that relationships between elements of similar incompatibility but with siderophile (W), chalcophile (Cu), and lithophile tendencies (Th, U, Yb) do not deviate from expected trends generated by magmatic differentiation during cooling and crystallization of mare basalts. These results, combined with chondrite-relative HSE abundances and near-chondritic measured 187Os/188Os compositions of primitive high-MgO mare basalts, imply that lunar mantle melts were generated from residual metal- and sulfide-free sources, or experienced complete exhaustion of metal and sulfides during partial melt extraction. Evidence for the loss of moderately volatile elements during lunar formation and early differentiation indicates that the BSM is >4 to 10 times more depleted in S than BSE. Because of an S-depleted BSM, mare basalt melts are unlikely to have reached S saturation, even if sulfide concentration at sulfide saturation (SCSS) was lowered relative to terrestrial values due to low lunar fO2. In the absence of residual sulfide or metal, resultant partial melt models indicate that a lunar mantle source with 25 to 75 μg/g S and high sulfide-melt partition coefficients can account for the chondritic-relative abundances of the HSE in mare basalts from a BSM that experienced <0.02% by mass of late accretion.