Tre’Shunda James^1,2 and Renyu Hu^1,3
Astrophysical Journal 867, 17 Link to Article [DOI: 10.3847/1538-4357/aae2bb]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
²Occidental College, Los Angeles, CA 90041, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA

Atmospheric chemistry models have shown that molecular oxygen can build up in CO₂-dominated atmospheres on potentially habitable exoplanets without input of life. Existing models typically assume a surface pressure of 1 bar. Here we present model scenarios of CO₂-dominated atmospheres with the surface pressure ranging from 0.1 to 10 bars, while keeping the surface temperature at 288 K. We use a one-dimensional photochemistry model to calculate the abundance of O₂ and other key species, for outgassing rates ranging from a Venus-like volcanic activity up to 20 times Earth-like activity. The model maintains the redox balance of the atmosphere and the ocean, and includes the pressure dependency of outgassing on the surface pressure. Our calculations show that the surface pressure is a controlling parameter in the photochemical stability and oxygen buildup of CO₂-dominated atmospheres. The mixing ratio of O₂ monotonically decreases as the surface pressure increases at very high outgassing rates, whereas it increases as the surface pressure increases at lower-than-Earth outgassing rates. Abiotic O₂ can only build up to the detectable level, defined as 10⁻³ in volume mixing ratio, in 10-bar atmospheres with the Venus-like volcanic activity rate and the reduced outgassing rate of H₂ due to the high surface pressure. Our results support the search for biological activities and habitability via atmospheric O₂ on terrestrial planets in the habitable zone of Sun-like stars.

¹Krivovichev, V.G.,²Charykova, M.V., ^3,4Krivovichev, S.V.
European Journal of Mineralogy 30, 219-230 Link to Article [DOI: 10.1127/ejm/2018/0030-2699]
¹Department of Mineralogy, Institute of Earth Sciences, St. Petersburg State University, University Emb. 7/9, St. Petersburg, 199034, Russian Federation
²Department of Geochemistry, Institute of Earth Sciences, St. Petersburg State University, University Emb. 7/9, St. Petersburg, 199034, Russian Federation
³Department of Crystallography, Institute of Earth Sciences, St. Petersburg State University, St. Petersburg, 199034, Russian Federation

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Åke V.Rosén^a, Jonas Pape^b, Beda A. Hofmann^a,b Edwin Gnos^c Marcel Guillong^d
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.11.016]
^aInstitute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, 3012 Bern, Switzerland
^bNatural History Museum Bern, Bernastrasse 15, 3005 Bern, Switzerland
^cNatural History Museum of Geneva, 1, Route de Malagnou, 1208 Geneva, Switzerland
^dInstitute of Geochemistry and Petrology, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland
Copyright Elsevier

Ureilites are the second largest group of achondrite meteorites but consensus is still lacking on the nature of their precursors, melting processes, and the genetic relationship between monomict ureilites and brecciated ureilites. The recently found ureilite Ramlat as Sahmah 517 is of special interest in this context. This meteorite lacks shock features in its primary silicates and belongs to a rare augite- and chromite-bearing subset of the monomict ferroan ureilites. It hosts abundant intergranular glass veinlets speckled with pyroxene and metal globules. Detailed petrographic investigations show that the Si-Al rich glass represents quenched anatectic melt that was present prior to formation of the reduced olivine rims by incomplete low-pressure equilibration (smelting) of carbon and silicates. The melt facilitated smelting which, along with rapid crystallization of secondary pyroxene, modified the originally trachyandesitic melt. Melt-silicate equilibrium preceding these events is constrained by modelling using MELTS and the first reported in-situ measurements of LREE-enriched glass that is largely complementary to the depleted mafic silicates in monomict ureilites. The inferred major element composition of the partial melt that formed in RaS 517 is similar to that of trachyandesite in Almahata Sitta but RaS 517 lacks phosphates which are abundant in the Almahata Sitta trachyandesite and in alkali-rich feldspathic clasts in polymict ureilites. The LREE-depletion in the dominant monomict ferroan ureilite population can be explained by the formation of melt fractions similar to the glass in RaS 517 after initial rapid melting of phosphates. These finds provide evidence for a genetic relationship between ferroan ureilites and lithologies similar to the Almahata Sitta trachyandesite and further suggest that these ureilites formed by partial melting of P- and alkali-rich precursors with trace element concentrations similar to equilibrated ordinary chondrites. Quenched Si-Al rich glass also occurs in magnesian ureilites but has lower concentrations of alkalis and LREE-depleted trace element signatures which can reflect more depleted compositions at the onset of partial melting. The evidence presented here favors a scenario in which the primary ureilite differentiation was driven by gradual heating from radioactive decay with resulting temperatures (>1100 °C) being maintained until disruption of the ureilite parent asteroid.

R. L. PALMA^1,2, R. O. PEPIN², A. J. WESTPHAL³, E.F€URI⁴, D. J. SCHLUTTER², Z.S.GAINSFORTH³, and D. R. FRANK⁵
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13189]
¹Department of Physics and Astronomy, Minnesota State University, Mankato, Minnesota 56001, USA
²School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA
³Space Sciences Laboratory, University of California, Berkeley, California 94720–7450, USA
⁴Centre de Recherches Petrographiques et Geochimiques, CNRS-UL, 54501 Vandoeuvre-les-Nancy Cedex, France
⁵Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, Hawai’i 96822, USA
Published by arrangement with John Wiley & Sons

Helium and neon distributions are reported for a variety of Stardust comet 81P/Wild 2 samples, including particle tracks and terminal particles, cell surface and subsurface slices from the comet coma and interstellar particle collection trays, and numerous small aerogel blocks extracted from comet cells C2044 and C2086. Discussions and conclusions in several abstracts published during the course of the investigation are included, along with the relevant data. Measured isotope ratios span a broad range, implying a similar range for noble gas carriers in the Wild 2 coma. The meteoritic phase Q‐²⁰Ne/²²Ne ratio was observed in several samples. Some of these, and others, exhibit ²¹Ne excesses too large for attribution to spallation by galactic cosmic ray irradiation, suggesting exposure to a solar proton flux greatly enhanced above current levels in an early near‐Sun environment. Still others display evidence for a solar wind component, particularly one C2086 block with large abundances of isotopically solar‐like helium and neon. Eighty‐nine small aerogel samples were cut from depths up to several millimeters below the cell C2044 surface and several millimeters away from the axis of major track T41. A fraction of these yielded measurable and variable helium and neon abundances and isotope ratios, although none contained visible tracks or carrier particle fragments and their locations were beyond estimated penetration ranges for small particles or ions incident on the cell surface, or for lateral ejecta from T41. Finding plausible emplacement mechanisms and sources for these gases is a significant challenge raised by this study.

Pinghui Huang^1,2,3, Andrea Isella⁴, Hui Li³, Shengtai Li³, and Jianghui Ji¹
Astrophysical Journal 867, 3 Link to Article [DOI: 10.3847/1538-4357/aae317]
¹CAS Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, People’s Republic of China
²University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
³Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
⁴Department of Physics & Astronomy, Rice University, 6100 Main Street, Houston, TX 77005, USA

Several nearby protoplanetary disks have been observed to display large-scale crescents in the (sub)millimeter dust continuum emission. One interpretation is that these structures correspond to anticyclonic vortices generated by the Rossby wave instability within the gaseous disk. Such vortices have local gas overdensities and are expected to concentrate dust particles with a Stokes number around unity. This process might catalyze the formation of planetesimals. Whereas recent observations showed that dust crescents are indeed regions where millimeter-size particles have abnormally high concentration relative to the gas and smaller grains, no observations have yet shown that the gas within the crescent region counterrotates with respect to the protoplanetary disk. Here we investigate the detectability of anticyclonic features through measurement of the line-of-sight component of the gas velocity obtained with ALMA. We carry out 2D hydrodynamic simulations and 3D radiative transfer calculations of a protoplanetary disk characterized by a vortex created by the tidal interaction with a massive planet. As a case study, the disk parameters are chosen to mimic the IRS 48 system, which has the most prominent crescent observed to date. We generate synthetic ALMA observations of both the dust continuum and ¹²CO emission around the frequency of 345 GHz. We find that the anticyclonic features of the vortex are weak but can be detected if both the source and the observational setup are properly chosen. We provide a recipe for maximizing the probability of detecting such vortex features and present an analysis procedure to infer their kinematic properties.

^1,2Britvin, S.N.,¹Murashko, M.N., ³Vapnik, Y., ¹Polekhovsky, Y.S., ^1,2Krivovichev, S.V., ¹Vereshchagin, O.S., ⁴Vlasenko, N.S., ⁴Shilovskikh, V.V., ¹Zaitsev, A.N.
Physics and Chemistry of Minerals (in Press) Link to Article [DOI: 10.1007/s00269-018-1008-4]
¹Institute of Earth Sciences, Saint-Petersburg State University, Universitetskaya Nab. 7/9, St. Petersburg, 199034, Russian Federation
²Nanomaterials Research Center, Kola Science Center of Russian Academy of Sciences, Fersman Str. 14, Apatity, Murmansk Region 184209, Russian Federation
³Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, POB 653, Beersheba, 84105, Israel
⁴Geomodel Resource Center, Saint Petersburg State University, Ulyanovskaya Str. 1, St. Petersburg, 198504, Russian Federation

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Ebert¹ et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13212]
¹Institut f€ur Planetologie, Westf€alische Wilhelms-Universit€at M€unster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany
Published by arrangement with John Wiley & Sons

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.

C. SÆTRE^1,2*, H. HELLEVANG^1,3, L. RIU⁴, H. DYPVIK^1,2, C. PILORGET⁴, F. POULET⁴, and S. C. WERNER^1,2
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13214]
¹Department of Geosciences, University of Oslo, P.O Box 1047 Blindern, N-0316 Oslo, Norway
²Centre for Earth Evolution and Dynamics, University of Oslo, P.O Box 1028 Blindern, N-0315 Oslo, Norway
³The University Centre in Svalbard (UNIS), Pb. 156, N-9171 Longyearbyen, Norway
⁴Institut d’Astrophysique Spatiale, B^atiment 121, CNRS/Universite Paris-Sud, 91405 Orsay Cedex, France
*Corresponding author. E-mail: christian.satre@geo.uio.no
Published by arrangement with John Wiley & Sons

Phyllosilicates, carbonates, zeolites, and sulfates on Mars give clues about the planet’s past environmental conditions, but little is known about the specific conditions in which these minerals formed within the crust and at the surface. The aim of the present study was to gain increased understanding on the formation of secondary phases by hydrothermal alteration of basaltic glass. The reaction processes were studied under varying conditions (temperature, pCO2, water:rock ratio, and fluid composition) with relevance to aqueous hydrothermal alteration in fully and partly saturated Martian basalt deposits. Analyses made on reaction products using X‐ray diffraction (XRD) and scanning electron microscope (SEM) were compared with near infrared spectroscopy (NIR) to establish relative detectability and spectral signatures. This study demonstrates that comparable alteration minerals (phyllosilicates, carbonates, zeolites) form from vapor condensing on mineral surfaces in unsaturated sediments and not only in fully water‐saturated sediments. In certain environments where water vapor might be present, it can alter the basaltic bedrock to a suite of authigenic phases similar to those observed on the Martian surface. For the detection of the secondary phases, XRD and SEM‐EDS were found to be superior to NIR for detecting and characterizing zeolites. The discrepancy in detectability of zeolites between NIR and XRD/SEM‐EDS might indicate that zeolites on Mars are more abundant than previously thought.

Amaya Moro-Martín
Astrophysical Journal 866, 131 Link to Article [DOI: 10.3847/1538-4357/aadf34]
Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA

1I/’Oumuamua is the first interstellar interloper to have been detected. Because planetesimal formation and ejection of predominantly icy objects are common by-products of the star and planet formation processes, in this study we address whether 1I/’Oumuamua could be representative of this background population of ejected objects. The purpose of the study of its origin is that it could provide information about the building blocks of planets in a size range that remains elusive to observations, helping to constrain planet formation models. We compare the mass density of interstellar objects inferred from its detection to that expected from planetesimal disks under two scenarios: circumstellar disks around single stars and wide binaries, and circumbinary disks around tight binaries. Our study makes use of a detailed study of the PanSTARRS survey volume; takes into account that the contribution from each star to the population of interstellar planetesimals depends on stellar mass, binarity, and planet presence; and explores a wide range of possible size distributions for the ejected planetesimals, based on solar system models and observations of its small-body population. We find that 1I/’Oumuamua is unlikely to be representative of a population of isotropically distributed objects, favoring the scenario that it originated from the planetesimal disk of a young nearby star whose remnants are highly anisotropic. Finally, we compare the fluxes of meteorites and micrometeorites observed on Earth to those inferred from this population of interstellar objects, concluding that it is unlikely that one of these objects is already part of the collected meteorite samples.

¹Potin, S.,¹Brissaud, O., ^1,2Beck, P., Schmitt, B., ¹Magnard, Y., ¹Correia, J.-J., ¹Rabou, P., ¹Jocou, L.
Applied Optics 57, 8279-8296 Link to Article [https://doi.org/10.1364/AO.57.008279]
¹University Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble, Grenoble, 38000, France
²Institut Universitaire de France, Paris, France

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