David V. BEKAERT¹, Guillaume AVICE^1,2, and Bernard MARTY¹
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13069]
¹Centre de Recherches Petrographiques et Geochimiques, UMR 7358 CNRS—Universite de Lorraine, 15 rue Notre Dame desPauvres, BP 20, 54501 Vandoeuvre-les-Nancy, France
²Present address: Division of Geology and Planetary Sciences, California Institute of Technology, 1200 E. California Blvd,Pasadena, California 91125, USA
Published by arrangement with John Wiley & Sons

Lunar basalt 15016 (~3.3 Ga) is among the most vesicular (50% by volume) basalts recovered by the Apollo missions. We investigated the possible occurrence of indigenous lunar nitrogen and noble gases trapped in vesicles within basalt 15016, by crushing several cm‐sized chips. Matrix/mineral gases were also extracted from crush residues by fusion with a CO₂ laser. No magmatic/primordial component could be identified; all isotope compositions, including those of vesicles, pointed to a cosmogenic origin. We found that vesicles contained ~0.2%, ~0.02%, ~0.002%, and ~0.02% of the total amount of cosmogenic ²¹Ne, ³⁸Ar, ⁸³Kr, and ¹²⁶Xe, respectively, produced over the basalt’s 300 Myr of exposure. Diffusion/recoil of cosmogenic isotopes from the basaltic matrix/minerals to intergrain joints and vesicles is discussed. The enhanced proportion of cosmogenic Xe isotopes relative to Kr detected in vesicles could be the result of kinetic fractionation, through which preferential retention of Xe isotopes over Kr within vesicles might have occurred during diffusion from the vesicle volume to the outer space through microleaks. This study suggests that cosmogenic loss, known to be significant for ³He and ²¹Ne, and to a lesser extent for ³⁶Ar (Signer et al. 1977), also occurs to a negligible extent for the heaviest noble gases Kr and Xe.

Scott D. KING¹, Julie C. CASTILLO-ROGEZ², M. J. TOPLIS³, Michael T. BLAND⁴, Carol A. RAYMOND², and Christopher T. RUSSELL⁵
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13063]
¹Department of Geosciences, Virginia Tech, Blacksburg, Virginia 24061, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109, USA
³Institut de Recherche d’Astrophysique et Planetologie, University of Toulouse, Toulouse, France
⁴US Geological Survey, Astrogeology Science Center, Flagstaff, Arizona 86001, USA
⁵Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095, USA
Published by arrangement with John Wiley & Sons

Thermal evolution modeling has yielded a variety of interior structures for Ceres, ranging from a modestly differentiated interior to more advanced evolution with a dry silicate core, a hydrated silicate mantle, and a volatile‐rich crust. Here we compute the mass and hydrostatic flattening from more than one hundred billion three‐layer density models for Ceres and describe the characteristics of the population of density structures that are consistent with the Dawn observations. We show that the mass and hydrostatic flattening constraints from Ceres indicate the presence of a high‐density core with greater than a 1σ probability, but provide little constraint on the density, allowing for core compositions that range from hydrous and/or anhydrous silicates to a mixture of metal and silicates. The crustal densities are consistent with surface observations of salts, water ice, carbonates, and ammoniated clays, which indicate hydrothermal alteration, partial fractionation, and the possible settling of heavy sulfide and metallic particles, which provide a potential process for increasing mass with depth.

Benoit Côté^1,2,8, Chris L. Fryer^2,3,8, Krzysztof Belczynski⁴, Oleg Korobkin^2,3, Martyna Chruślińska⁵, Nicole Vassh⁶, Matthew R. Mumpower^2,3,7, Jonas Lippuner^2,3, Trevor M. Sprouse⁶, Rebecca Surman^2,6
Astrophysical Journal 855, 99 Link to Article [DOI: 10.3847/1538-4357/aaad67]
¹Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary
²Joint Institute for Nuclear Astrophysics—Center for the Evolution of the Elements, USA
³Center for Theoretical Astrophysics, LANL, Los Alamos, NM 87545, USA
⁴Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716 Warsaw, Poland
⁵Institute of Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen, P.O. box 9010, 6500 GL Nijmegen, the Netherlands
⁶University of Notre Dame, Notre Dame, IN 46556, USA
⁷Theoretical Division, Los Alamos National Lab, Los Alamos, NM 87545, USA
⁸NuGrid Collaboration, http://nugridstars.org.

Some of the heavy elements, such as gold and europium (Eu), are almost exclusively formed by the rapid neutron capture process (r-process). However, it is still unclear which astrophysical site between core-collapse supernovae and neutron star–neutron star (NS–NS) mergers produced most of the r-process elements in the universe. Galactic chemical evolution (GCE) models can test these scenarios by quantifying the frequency and yields required to reproduce the amount of europium (Eu) observed in galaxies. Although NS–NS mergers have become popular candidates, their required frequency (or rate) needs to be consistent with that obtained from gravitational wave measurements. Here, we address the first NS–NS merger detected by LIGO/Virgo (GW170817) and its associated gamma-ray burst and analyze their implication for the origin of r-process elements. The range of NS–NS merger rate densities of 320–4740 Gpc⁻³ yr⁻¹ provided by LIGO/Virgo is remarkably consistent with the range required by GCE to explain the Eu abundances in the Milky Way with NS–NS mergers, assuming the solar r-process abundance pattern for the ejecta. Under the same assumption, this event has produced about 1–5 Earth masses of Eu, and 3–13 Earth masses of gold. When using theoretical calculations to derive Eu yields, constraining the role of NS–NS mergers becomes more challenging because of nuclear astrophysics uncertainties. This is the first study that directly combines nuclear physics uncertainties with GCE calculations. If GW170817 is a representative event, NS–NS mergers can produce Eu in sufficient amounts and are likely to be the main r-process site.

Yutaka Hirai^1,2,7, Takayuki R. Saitoh³, Yuhri Ishimaru^4,8, and Shinya Wanajo^5,6
Astrophysical Journal 855, 63 Link to Article [DOI: 10.3847/1538-4357/aaaabc]
¹Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
⁴Department of Natural Sciences, College of Liberal Arts, International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan
⁵Department of Engineering and Applied Sciences, Faculty of Science and Technology, Sophia University, 7-1 Kioicho, Chiyoda-ku, Tokyo 102-8554, Japan
⁶RIKEN, iTHES Research Group, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
⁷JSPS Research Fellow.
⁸Deceased 2017 November 18.

The heaviest iron-peak element Zinc (Zn) has been used as an important tracer of cosmic chemical evolution. Spectroscopic observations of the metal-poor stars in Local Group galaxies show an increasing trend of [Zn/Fe] ratios toward lower metallicity. However, the enrichment of Zn in galaxies is not well understood due to poor knowledge of astrophysical sites of Zn, as well as metal mixing in galaxies. Here we show possible explanations for the observed trend by taking into account electron-capture supernovae (ECSNe) as one of the sources of Zn in our chemodynamical simulations of dwarf galaxies. We find that the ejecta from ECSNe contribute to stars with [Zn/Fe]  0.5. We also find that scatters of [Zn/Fe] in higher metallicities originate from the ejecta of type Ia supernovae. On the other hand, it appears difficult to explain the observed trends if we do not consider ECSNe as a source of Zn. These results come from an inhomogeneous spatial metallicity distribution due to the inefficiency of the metal mixing. We find that the optimal value of the scaling factor for the metal diffusion coefficient is ~0.01 in the shear-based metal mixing model in smoothed particle hydrodynamics simulations. These results suggest that ECSNe could be one of the contributors of the enrichment of Zn in galaxies.