Quan-Zhi Ye (叶泉志)^1,2, Qicheng Zhang³, Michael S. P. Kelley⁴, and Peter G. Brown^5,6
Astrophysical Journal Letters 851, L5 Link to Article [DOI: 10.3847/2041-8213/aa9a34]
¹Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
²Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
⁴Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁵Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
⁶Centre for Planetary Science and Exploration, The University of Western Ontario, London, ON N6A 5B8, Canada

1I/2017 U1 (‘Oumuamua), a recently discovered asteroid in a hyperbolic orbit, is likely the first macroscopic object of extrasolar origin identified in the solar system. Here, we present imaging and spectroscopic observations of ‘Oumuamua using the Palomar Hale Telescope as well as a search of meteor activity potentially linked to this object using the Canadian Meteor Orbit Radar. We find that ‘Oumuamua exhibits a moderate spectral gradient of , a value significantly lower than that of outer solar system bodies, indicative of a formation and/or previous residence in a warmer environment. Imaging observation and spectral line analysis show no evidence that ‘Oumuamua is presently active. Negative meteor observation is as expected, since ejection driven by sublimation of commonly known cometary species such as CO requires an extreme ejection speed of ~40 m s⁻¹ at ~100 au in order to reach the Earth. No obvious candidate stars are proposed as the point of origin for ‘Oumuamua. Given a mean free path of ~10⁹ ly in the solar neighborhood, ‘Oumuamua has likely spent a very long time in interstellar space before encountering the solar system.

Arshad ALI^1,2, Iffat JABEEN², Neil R. BANERJEE², Gordon R. OSINSKI^2,3, Ian NICKLIN⁴, David GREGORY⁵, and Patrick HERRMANN⁶
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13072]
¹Earth Sciences Research Centre (ESRC), Sultan Qaboos University, Al-Khoudh, Muscat 123, Sultanate of Oman
²Department of Earth Sciences/Centre for Planetary Science and Exploration (CPSX), University of Western Ontario, London,Ontario, Canada
³Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada
⁴Department of Natural History, Royal Ontario Museum, Toronto, Ontario N5R 4P5, Canada
⁵230 First Ave., Suite 108, St. Thomas, Ontario, Canada
⁶Pallasite.ca, Toronto, Ontario, Canada
Published by arrangement with John Wiley & Sons

Oxygen isotope measurements of olivine in main group (MG) pallasites by traditional laser fluorination method are associated with some uncertainties including terrestrial weathering, incomplete olivine reaction, and sample state. We improved our laser fluorination approach by pretreating olivine grains with acid to remove terrestrial weathering products and by modifying the sample holder for an efficient and complete laser reaction. Our experiments on Brahin olivine demonstrate that acid‐washing successfully removes the terrestrial weathering with <0.1‰ variation in δ¹⁸O value and, at the same time, improving the ∆¹⁷O value significantly. We also achieved a complete olivine fluorination by employing a custom‐designed sample holder with “V”‐shaped profile having rounded bottom because incomplete/partial reaction of olivine gives comparatively lighter δ¹⁸O values. Using these new techniques, we present precise triple oxygen isotope data (N = 72) of 25 olivine samples separated from main group pallasites. The data are, on average, ~0.5‰ heavier in δ¹⁸O relative to the values published in the literature for the same samples. Critically, the ∆¹⁷O values of MG pallasites and to some extent their Fo‐contents suggest that there are at least two populations of olivine. Based on our improved data set, we propose that MG pallasites potentially have high‐∆¹⁷O‐ and low‐∆¹⁷O‐bearing subgroups that are statistically distinct. The subgroups present average ∆¹⁷O values of −0.166 ± 0.003 (2SE; N = 16) and −0.220 ± 0.003 (2SE; N = 9), respectively. Furthermore, the high‐∆¹⁷O‐bearing subgroup samples trend toward lower Fo‐contents compared to the other subgroup. Taken together, our data provide evidence that argues against a single parent body origin for MG pallasites.

Christian Iliadis^1,2, Lori N. Downen^1,2, Jordi José^3,4, Larry R. Nittler⁵, and Sumner Starrfield⁶
Astrophysical Journal 855, 76 Link to Article [DOI: 10.3847/1538-4357/aaabb6]
¹Department of Physics & Astronomy, University of North Carolina, Chapel Hill, NC 27599-3255, USA
²Triangle Universities Nuclear Laboratory, Durham, NC 27708-0308, USA
³Departament de Física, EEBE, Universitat Politècnica de Catalunya, c/Eduard Maristany 10, E-08930 Barcelona, Spain
⁴Institut d’Estudis Espacials de Catalunya, c/Gran Capità 2-4, Ed. Nexus-201, E-08034 Barcelona, Spain
⁵Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington, DC 20015, USA
⁶Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA

About 30%–40% of classical novae produce dust 20–100 days after the outburst, but no presolar stardust grains from classical novae have been unambiguously identified yet. Although several studies claimed a nova paternity for certain grains, the measured and simulated isotopic ratios could only be reconciled, assuming that the grains condensed after the nova ejecta mixed with a much larger amount of close-to-solar matter. However, the source and mechanism of this potential post-explosion dilution of the ejecta remains a mystery. A major problem with previous studies is the small number of simulations performed and the implied poor exploration of the large nova parameter space. We report the results of a different strategy, based on a Monte Carlo technique, that involves the random sampling over the most important nova model parameters: the white dwarf composition; the mixing of the outer white dwarf layers with the accreted material before the explosion; the peak temperature and density; the explosion timescales; and the possible dilution of the ejecta after the outburst. We discuss and take into account the systematic uncertainties for both the presolar grain measurements and the simulation results. Only those simulations that are consistent with all measured isotopic ratios of a given grain are accepted for further analysis. We also present the numerical results of the model parameters. We identify 18 presolar grains with measured isotopic signatures consistent with a CO nova origin, without assuming any dilution of the ejecta. Among these, the grains G270_2, M11-334-2, G278, M11-347-4, M11-151-4, and Ag2_6 have the highest probability of a CO nova paternity.

Yuri Aikawa¹, Kenji Furuya², Ugo Hincelin³, and Eric Herbst³
Astrophysical Journal 855, 119 Link to Article [DOI: 10.3847/1538-4357/aaad6c]
¹Department of Astronomy, The University of Tokyo, Japan
²Center for Computational Sciences, University of Tsukuba, Japan
³Department of Chemistry, The University of Virginia, Charlottesville, VA, USA

We investigate deuterium chemistry coupled with the nuclear spin-state chemistry of H₂ and in protoplanetary disks. Multiple paths of deuterium fractionation are found; exchange reactions with D atoms, such as HCO⁺ + D, are effective in addition to those with HD. In a disk model with grain sizes appropriate for dark clouds, the freeze-out of molecules is severe in the outer midplane, while the disk surface is shielded from UV radiation. Gaseous molecules, including DCO⁺, thus become abundant at the disk surface, which tends to make their column density distribution relatively flat. If the dust grains have grown to millimeter size, the freeze-out rate of neutral species is reduced and the abundances of gaseous molecules, including DCO⁺ and N₂D⁺, are enhanced in the cold midplane. Turbulent diffusion transports D atoms and radicals at the disk surface to the midplane, and stable ice species in the midplane to the disk surface. The effects of turbulence on chemistry are thus multifold; while DCO⁺ and N₂D⁺ abundances increase or decrease depending on the regions, HCN and DCN in the gas and ice are greatly reduced at the innermost radii, compared to the model without turbulence. When cosmic rays penetrate the disk, the ortho-to-para ratio (OPR) of H₂ is found to be thermal in the disk, except in the cold (10 K) midplane. We also analyze the OPR of and H₂D⁺, as well as the main reactions of H₂D⁺, DCO⁺, and N₂D⁺, in order to analytically derive their abundances in the cold midplane.

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.

Dominik C. Hezel^a,b,c, Johanna S. Wilden^a, Daniel Becker^a, Sonja Steinbach^d, Frank Wombacher^a,c, Markus Harak^a
Earth and Planetary Science Letters 490, 31-39 Link to Article [https://doi.org/10.1016/j.epsl.2018.03.013]
^aUniversity of Cologne, Department of Geology and Mineralogy, Zülpicher Str. 49b, 50674 Köln, Germany
^bNatural History Museum, Department of Mineralogy, Cromwell Road, SW7 5BD, London, UK
^cSteinmann-Institut, Poppelsdorfer Schloss, Meckenheimer Allee 169, 53115 Bonn, Germany
^dDeutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Materialphysik im Weltraum, Linder Höhe, 51147 Köln, Germany
Copyright Elsevier

Chondrules are a major constituent of primitive meteorites. The formation of chondrules is one of the most elusive problems in cosmochemistry. We use Fe isotope compositions of chondrules and bulk chondrites to constrain the conditions of chondrule formation. Iron isotope compositions of bulk chondrules are so far only known from few studies on CV and some ordinary chondrites. We studied 37 chondrules from the CM chondrite Murchison. This is particularly challenging, as CM chondrites contain the smallest chondrules of all chondrite groups, except for CH chondrites. Bulk chondrules have δ⁵⁶Fe between −0.62 and +0.24‰ relative to the IRMM-014 standard. Bulk Murchison has as all chondrites a δ⁵⁶Fe of 0.00‰ within error. The δ⁵⁶Fe distribution of the Murchison chondrule population is continuous and close to normal. The width of the δ⁵⁶Fe distribution is narrower than that of the Allende chondrule population. Opaque modal abundances in Murchison chondrules is in about 67% of the chondrules close to 0 vol.%, and in 33% typically up to 6.5 vol.%. Chondrule Al/Mg and Fe/Mg ratios are sub-chondritic, while bulk Murchison has chondritic ratios. We suggest that the variable bulk chondrule Fe isotope compositions were established during evaporation and recondensation prior to accretion in the Murchison parent body. This range in isotope composition was likely reduced during aqueous alteration on the parent body. Murchison has a chondritic Fe isotope composition and a number of chondritic element ratios. Chondrules, however, have variable Fe isotope compositions and chondrules and matrix have complementary Al/Mg and Fe/Mg ratios. In combination, this supports the idea that chondrules and matrix formed from a single reservoir and were then accreted in the parent body. The formation in a single region also explains the compositional distribution of the chondrule population in Murchison.

Keisuke Sakuma¹, Hiroshi Hidaka¹, and Shigekazu Yoneda²

Astrophysical Journal 853, 92 Link to Article [DOI: 10.3847/1538-4357/aaa1e3]
¹Department of Earth and Planetary Sciences, Nagoya University Nagoya 464-8601, Japan
²Department of Science and Engineering, National Museum of Nature and Science Tsukuba 305-0005, Japan

Aqueous alteration is one of the primitive activities that occurred on meteorite parent bodies in the early solar system. The Tagish Lake meteorite is known to show an intense parent body aqueous alteration signature. In this study, quantitative analyses of the alkaline elements and isotopic analyses of Sr and Ba from acid leachates of TL (C2-ungrouped) were performed to investigate effects of aqueous alteration. The main purpose of this study is to search for isotopic evidence of extinct ¹³⁵Cs from the Ba isotopic analyses in the chemical separates from the Tagish Lake meteorite. Barium isotopic data from the leachates show variable ¹³⁵Ba isotopic anomalies (ε = −2.6 ~ +3.6) which correlatewith ¹³⁷Ba and ¹³⁸Ba suggesting a heterogeneous distribution of s– and r-rich nucleosynthetic components in the early solar system. The ⁸⁷Rb–⁸⁷Sr and ¹³⁵Cs–¹³⁵Ba decay systems on TL in this study do not provide any chronological information. The disturbance of the TL chronometers is likely a reflection of the selective dissolution of Cs and Rb given the relatively higher mobility of Cs and Rb compared to Ba and Sr, respectively, during fluid mineral interactions.