Roman R. Rafikov^1,2
The Astrophysical Journal 861, 35 Link to Article [https://doi.org/10.3847/1538-4357/aac5ef]
¹Centre for Mathematical Sciences, Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
²Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540, USA

Discovery of the first interstellar asteroid (ISA)—1I/2017 ‘Oumuamua—raised natural questions regarding its origin, some related to its lack of cometary activity, suggesting refractory composition. Here we explore the possibility that ‘Oumuamua-like ISAs are produced in tidal disruption events (TDEs) of refractory planetoids (asteroids, terrestrial planets, etc.) by white dwarfs (WDs). This idea is supported by spectroscopic observations of metal-polluted WDs, indicating the predominantly volatile-poor composition of the accreted material. We show that such TDEs sourced by realistic planetary systems (including a population of 10³ km planetoids and massive perturbers—Neptune-to-Saturn mass planets) can eject up to 30% of planetary mass involved in TDEs to interstellar space. Collisional fragmentation, caused by vertical collapse of the disrupted planetoid’s debris inside the WD Roche sphere, channels most of its mass into 0.1–1 km fragments, similar to ‘Oumuamua. Such a size spectrum of ISAs (very different from the top-heavy distributions expected in other scenarios) implies that planetary TDEs can account for a significant fraction (up to ~30%) of ISAs. This figure is based on existing observations of WD metal pollution, which are de-biased using realistic models of circum-WD planetary systems. Such ISAs should exhibit kinematic characteristics of old, dynamically hot Galactic populations. ISA ejection in individual planetary TDEs is highly anisotropic, resulting in large fluctuations of their space density. We also show that other ISA production channels involving stellar remnants—direct ejection by massive planets around the WDs and supernova explosions—have difficulty explaining ‘Oumuamua-like ISAs.

Oliver Philcox^1,2, Jan Rybizki², and Thales A. Gutcke²
The Astrophysical Journal 861, 40 Link to Article [https://doi.org/10.3847/1538-4357/aac6e4]
¹Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
²Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany

To fully harvest the rich library of stellar elemental abundance data available, we require reliable models that facilitate our interpretation of them. Galactic chemical evolution (GCE) models are one such set, a key part of which are the selection of chemical yields from different nucleosynthetic enrichment channels, predominantly asymptotic giant branch stars, Type Ia supernovae (SNe Ia), and core-collapse supernovae (CC-SNe). Here we present a scoring system for yield tables based on their ability to reproduce protosolar abundances within a simple parameterization of the GCE modeling software Chempy, which marginalizes over galactic parameters describing simple stellar populations (SSPs) and interstellar medium physics. Two statistical scoring methods are presented, based on Bayesian evidence and leave-one-out cross-validation, and are applied to five CC-SN tables, for (a) all mutually available elements and (b) a subset of the nine most abundant elements. We find that the yields of Prantzos et al. (P18, including stellar rotation) and Chieffi & Limongi (C04) best reproduce protosolar abundances for the two cases, respectively. The inferred best-fit SSP parameters for case (b) are for the initial mass function high-mass slope and for the SN Ia normalization, which are broadly consistent across tested yield tables. Additionally, we demonstrate how Chempy can be used to dramatically improve elemental abundance predictions of hydrodynamical simulations by plugging tailored best-fit SSP parameters into a Milky Way analog from Gutcke & Springel. Our code, including a comprehensive tutorial, is freely available and can additionally provide SSP enrichment tables for any combination of parameters and yield tables.

Andreas Schreiber¹ and Hubert Klahr
The Astrophysical Journal 861, 47 Link to Article [https://doi.org/10.3847/1538-4357/aac3d4]
¹Fellow of the International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg (IMPRS-HD).

The collapse of dust particle clouds directly to kilometer-sized planetesimals is a promising way to explain the formation of planetesimals, asteroids, and comets. In the past, this collapse has been studied in stratified shearing box simulations with super-solar dust-to-gas ratio , allowing for streaming instability (SI) and gravitational collapse. This paper studies the non-stratified SI under dust-to-gas ratios from up to without self-gravity. The study covers domain sizes of , , and in terms of the gas-disk scale height using the PencilCode. They are performed in radial-azimuthal (2D) and radial-vertical (2.5D) extents. The used particles of and 0.1 mark the upper end of the expected dust growth. SI activity is found up to very high dust-to-gas ratios, providing fluctuations in the local dust-to-gas ratios and turbulent particle diffusion δ. We find an SI-like instability that operates in r–, even when vertical modes are suppressed. This new azimuthal streaming instability (aSI) shows similar properties and appearance as the SI. Both, SI and aSI show diffusivity at only to be two orders of magnitude lower than at , suggesting a relation that is shallow around . The (a)SI ability to concentrate particles is found to be uncorrelated with its strength in particle turbulence. Finally, we performed a resolution study to test our findings of the aSI. This paper stresses the importance of properly resolving the (a)SI at high dust-to-gas ratios and planetesimal collapse simulations, leading otherwise to potentially incomplete results.

Christopher N. Shingledecker¹, Jessica Tennis¹, Romane Le Gal^1,2, and Eric Herbst^1,3
The Astrophysical Journal 861, 20 Link to Article [https://doi.org/10.3847/1538-4357/aac5ee]
¹Department of Chemistry, University of Virginia Charlottesville, VA 22904, USA
²Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
³Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA

In this paper, we present preliminary results illustrating the effect of cosmic rays on solid-phase chemistry in models of both TMC-1 and several sources with physical conditions identical to TMC-1 except for hypothetically enhanced ionization rates. Using a recent theory for the addition of cosmic-ray-induced reactions to astrochemical models, we calculated the radiochemical yields, called G values, for the primary dust grain ice-mantle constituents. We show that the inclusion of this nonthermal chemistry can lead to the formation of complex organic molecules from simpler ice-mantle constituents, even under cold core conditions. In addition to enriching ice mantles, we find that these new radiation-chemical processes can lead to increased gas-phase abundances as well, particularly for HOCO, NO₂, HC₂O, methyl formate (HCOOCH₃), and ethanol (CH₃CH₂OH). These model results imply that HOCO—and perhaps NO₂—might be observable in TMC-1. Future detections of either of these two species in cold interstellar environments could provide strong support for the importance of cosmic-ray-driven radiation chemistry. The increased gas-phase abundance of methyl formate can be compared with abundances achieved through other formation mechanisms such as pure gas-phase chemistry and surface reactions.

^1,2Joshua F.Snape, ^3,4Natalie M.Curran,¹Martin J.Whitehouse, ^1,5Alexander A.Nemchin, ³Katherine H.Joy, ⁶Tom Hopkinson, ^6,7Mahesh Anand, ¹Jeremy J.Bellucci, ¹Gavin G.Kenny
Earth and Planetary Science Letters 502, 84-95 Link to Article [https://doi.org/10.1016/j.epsl.2018.08.035]
¹Department of Geosciences, Swedish Museum of Natural History, SE-104 05 Stockholm, Sweden
²Department of Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
³School of Earth and Environmental Sciences (SEES), University of Manchester, Oxford Road, Manchester M13 9PL, UK
⁴NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
⁵Department of Applied Geology, Curtin University, Perth, WA 6845, Australia
⁶School of Physical Science, The Open University, Milton Keynes, MK7 6AA, UK
⁷Department of Earth Sciences, The Natural History Museum, London, SW7 5BD, UK
Copyright Elsevier

Lunar meteorites provide a potential opportunity to expand the study of ancient (>4000 Ma) basaltic volcanism on the Moon, of which there are only a few examples in the Apollo sample collection. Secondary Ion Mass Spectrometry (SIMS) was used to determine the Pb isotopic compositions of multiple mineral phases (Ca-phosphates, baddeleyite K-feldspar, K-rich glass and plagioclase) in two lunar meteorites, Miller Range (MIL) 13317 and Kalahari (Kal) 009. These data were used to calculate crystallisation ages of 4332±2Ma (95% confidence level) for basaltic clasts in MIL 13317, and 4369±7Ma (95% confidence level) for the monomict basaltic breccia Kal 009. From the analyses of the MIL 13317 basaltic clasts, it was possible to determine an initial Pb isotopic composition of the protolith from which the clasts originated, and infer a 238U/204Pb ratio (μ-value) of 850±130(2σ uncertainty) for the magmatic source of this basalt. This is lower than μ-values determined previously for KREEP-rich (an acronym for K, Rare Earth Elements and P) basalts, although analyses of other lithological components in the meteorite suggest the presence of a KREEP component in the regolith from which the breccia was formed and, therefore, a more probable origin for the meteorite on the lunar nearside. It was not possible to determine a similar initial Pb isotopic composition from the Kal 009 data, but previous studies of the meteorite have highlighted the very low concentrations of incompatible trace elements and proposed an origin on the farside of the Moon. Taken together, the data from these two meteorites provide more compelling evidence for widespread ancient volcanism on the Moon. Furthermore, the compositional differences between the basaltic materials in the meteorites provide evidence that this volcanism was not an isolated or localised occurrence, but happened in multiple locations on the Moon and at distinct times. In light of previous studies into early lunar magmatic evolution, these data also imply that basaltic volcanism commenced almost immediately after Lunar Magma Ocean (LMO) crystallisation, as defined by Nd, Hf and Pb model ages at about 4370 Ma.

^1,2Agata M. Krzesińska, ¹Natasha V. Almeida
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13190]
¹Department of Earth Sciences, Natural History Museum, London, UK
²Institute of Geological Sciences, Polish Academy of Sciences, Wrocław, Poland
Published by arrangement with John Wiley & Sons

Baszkówka is an equilibrated, apparently low‐shock, unusually porous chondrite. Some earlier studies were undertaken to understand whether the porosity in Baszkówka, and similar porous chondrites, is a relic of a primordial feature or rather the effect of atypical reprocessing on the parent body. Neither of the studies reconstructed the accurate thermal and deformational evolution of chondrites, however, while it is known that shock‐induced compaction is the main means to affect chondritic porosity. Here we use a combination of 3‐D and 2‐D petrographic examination to understand how the evolution of pores correlates with thermal and shock history recorded in the Baszkówka chondrite. The grain framework silicates in Baszkówka contain healed shock fractures—a clear recorder of significant shock process and postshock annealing. Simultaneously, metal grains do not exhibit any preferred orientation or fabric, which would be expected to develop in response to the deformation as recorded by silicates. We interpret this as evidence for re‐agglomeration and annealing of shocked material. Pore spaces in Baszkówka are connected and decorated by fine‐grained plagioclase‐dominated mass and bulky euhedral olivine crystals, which exhibit growth steps on crystal surfaces. The euhedral olivine must have formed owing to the condensation of a vapor, while plagioclase most likely crystallized from melted chondritic matrix. During the shock event, fine‐grained matrix in Baszkówka was melted and vaporized. Vapor expansion added to ballistic velocity led to ejection and opening of the pore spaces. After re‐agglomeration in a hot ejecta blanket the rock was annealed, melted material circulated in created pore spaces and vapor condensed.

¹Edwin Gnos, ¹Beda A. Hofmann, ²Khalid Al‐Wagdani,²Ayman Mahjub, ²Abdulaziz Abdullah Al‐Solami, ²Siddiq N. Habibullah, ³Albert Matter, ²Mohammed A. Halawani
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13187]
¹Natural History Museum Geneva, CP 6434, Geneva 6, Switzerland
²Saudi Geological Survey, Jiddah, Saudi Arabia
³Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

The ~5.5 km sized Jabal Rayah ring structure located at 28°39′N/37°12′E in Saudi Arabia has been classified as a possible complex impact structure located in flat‐lying Paleozoic clastic sediments. Previous, detailed mapping showed that erosional processes led to a relief inversion, with displaced, folded, and faulted blocks of Silurian to Early Devonian strata, interpreted to form a ring syncline, now forming a topographically outstanding, 150 m high ring crest. The drainage toward the center of the structure seems controlled by a set of radial faults. This central part is eroded to the level of the surrounding plateau and partially covered with gravel. Analysis of 28 Qusaiba Formation sandstones showed that at the present outcrop level, the sediments seem devoid of shock features. Measurement of fold axes in the central part of the structure shows radially outward plunging fold axes, becoming steeper toward the center, and also fold axes of other orientation, and folded folds. This fold axis pattern is interpreted as an upward‐pointing, kilometer‐sized sheath fold. Assuming an impact scenario and using the present size of the structure, the minimum central structural uplift is estimated at ~500 m, which is consistent with Qusaiba Formation occupying the center of the ring structure.

¹Zhong-Yi Lin, ¹Wing-Huen Ip, ¹Chow-Choong Ngeow
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.07.012]
¹No. 300, Zhongda Rd., Zhongli Dist, Taoyuan City, 32001, Taiwan

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹William Abbey et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.09.004]
¹Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109
Copyright Elsevier

The Mars Science Laboratory (MSL) rover, Curiosity, completed its first Martian year, 669 sols (687 Earth days), of operation on June 24, 2014. During that time the rover successfully drilled three full depth drill holes into the Martian surface and analyzed the recovered material using onboard instruments, giving us new insights into the potential habitability of ancient Mars. These drill targets are known as ‘John Klein’ (Sol 182) and ‘Cumberland’ (Sol 279), which lie in the mudstones of the Yellowknife Bay formation, and ‘Windjana’ (Sol 621), which lies in the sandstones of the Kimberley formation. In this paper we will discuss what was necessary to procure these samples, including: 1) an overview of the sampling hardware; 2) the steps taken to ensure sampling hardware is safe when drilling into a target (i.e., evaluation of rock type, rover stability, prior testbed experience, etc.); and 3) the drilling parameters used to acquire these samples. We will also describe each target individually and discuss why each sample was desired, the triage steps taken to ensure it could be safely acquired, and the telemetry obtained for each. Finally, we will present scientific highlights obtained from each site utilizing MSL’s onboard instrumentation (SAM & CheMin), results enabled by the drills ability to excavate sample at depth and transfer it to these instruments.

¹Pieter Vermeesch
Earth and Planetary Science Letters 501, 112-118 Link to Article [https://doi.org/10.1016/j.epsl.2018.08.019]
¹Department of Earth Sciences, University College London, United Kingdom
Copyright Elsevier

Point-counting data are a mainstay of petrography, micropalaeontology and palynology. Conventional statistical analysis of such data is fraught with problems. Commonly used statistics such as the arithmetic mean and standard deviation may produce nonsensical results when applied to point-counting data. This paper makes the case that point-counts represent a distinct class of data that requires different treatment. Point-counts are affected by a combination of (1) true compositional variability and (2) multinomial counting uncertainties. The relative magnitude of these two sources of dispersion can be assessed by a chi-square statistic and test. For datasets that pass the chi-square test for homogeneity, the ‘pooled’ composition is shown to represent the optimal estimate for the underlying population. It is obtained by simply adding together the counts of all samples and normalising the resulting values to unity. However, more often than not, point-counting datasets fail the chi-square test. The overdispersion of such datasets can be captured by a random effects model that combines a logistic normal population with the usual multinomial counting uncertainties. This gives rise to the concept of a ‘central’ composition as a more appropriate way to average overdispersed data. Two- or three-component datasets can be displayed on radial plots and ternary diagrams, respectively. Higher dimensional datasets may be visualised and interpreted by Correspondence Analysis (CA). This is a multivariate ordination technique that is similar in purpose to Principal Component Analysis (PCA). CA and PCA are both shown to be special cases of Multidimensional Scaling (MDS). Generalising this insight to multiple datasets allows point-counting data to be combined with other data types such as chemical compositions by means of 3-way MDS. All the techniques introduced in this paper have been implemented in the provenance R-package, which is available from http://provenance.london-geochron.com.