Maximilien J. VERDIER-PAOLETTI^1,2, Yves MARROCCHI³, Lionel G. VACHER^3,4,Jerome GATTACCECA⁵, Andrey GURENKO³, Corinne SONZOGNI⁵, andMatthieu GOUNELLE^1,6
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13306]
¹IMPMC, MNHN, UPMC, UMR CNRS 7590, 61 rue Buffon, 75005 Paris, France
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, District of Columbia 20015, USA
³CRPG, CNRS, Universite de Lorraine, UMR 7358, Vandoeuvre les Nancy F-54501, France
⁴Department of Physics, Washington University, St. Louis, St. Louis, Missouri 63130, USA
⁵CNRS, Aix-Marseille Univ, IRD, Coll France, CEREGE, Aix-en-Provence, France
⁶Institut Universitaire de France, Maison des Universites, 103 bd. Saint-Michel, 75005 Paris, France
Published by arrangement with John Wiley & Sons

Boriskino is a poorly studied CM chondrite with numerous millimeter‐ to centimeter‐scale clasts exhibiting sharp boundaries. Clast textures and mineralogies attest to diverse geological histories with various degrees of aqueous alteration. We conducted a petrographic, chemical, and isotopic study on each clast type of the breccia to investigate if there exists a genetic link between brecciation and aqueous alteration, and to determine the controlling parameter of the extent of alteration. Boriskino is dominated by CM2 clasts for which no specific petrographic type could be assigned based on the chemical compositions and modal abundances of constituents. One clast stands out and is identified as a CM1 lithology, owing to its lack of anhydrous silicates and its overall abundance of dolomite‐like carbonates and acicular iron sulfides. We observe that alteration phases near clast boundaries exhibit foliation features, suggesting that brecciation postdated aqueous alteration. We measured the O‐isotopic composition of Ca‐carbonates and dolomite‐like carbonates to determine their precipitation temperatures following the methodology of Verdier‐Paoletti et al. (2017). Both types of carbonates yield similar ranges of precipitation temperatures independent of clast lithology, ranging from −13.9 ± 22.4 (2σ) to 166.5 ± 47.3 °C, precluding that temperature alone accounts for the differences between the CM1 and CM2 lithologies. Instead, we suggest that initial water/rock ratios of 0.75 and 0.61 for the CM1 and CM2 clasts, respectively, might control the extent of aqueous alteration. Based on these estimates, we suggest that Boriskino clasts originated from a single parent body with heterogeneous distribution of water either due to local differences in the material permeability or in the initial content of ice available. These conditions would have produced microenvironments with differing geochemical conditions thus leading to a range of degrees of aqueous alteration.

Birger Schmitz
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13308]
Astrogeobiology Laboratory, Department of Physics, Lund University, Lund, Sweden
Published by arrangement with John Wiley & Sons

One of the major frontiers in science today is the search for exoplanets, …

S. Holm-Alwmark et al. (>10)^1,2,3
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13309]
¹Department of Geology, Lund University, Solvegatan 12, SE-22362 Lund, Sweden
²Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
³Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

The Puchezh‐Katunki impact structure, 40–80 km in diameter, located ~400 km northeast of Moscow (Russia), has a poorly constrained age between ~164 and 203 Ma (most commonly quoted as 167 ± 3 Ma). Due to its relatively large size, the Puchezh‐Katunki structure has been a prime candidate for discussions on the link between hypervelocity impacts and extinction events. Here, we present new ⁴⁰Ar/³⁹Ar data from step‐heating analysis of five impact melt rock samples that allow us to significantly improve the age range for the formation of the Puchezh‐Katunki impact structure to 192–196 Ma. Our results also show that there is not necessarily a simple relationship between the observed petrographic features of an impact melt rock sample and the obtained ⁴⁰Ar/³⁹Ar age spectra and inverse isochrons. Furthermore, a new palynological investigation of the postimpact crater lake sediments supports an age significantly older than quoted in the literature, i.e., in the interval late Sinemurian to early Pliensbachian, in accordance with the new radioisotopic age estimate presented here. The new age range of the structure is currently the most reliable age estimate of the Puchezh‐Katunki impact event.

I. J. M. Crossfield¹, J. D. Lothringer², B. Flores^1,3, E. A. C. Mills⁴, R. Freedman^5,6, J. Valverde^1,7,8, B. Miles⁹, X. Guo¹, and A. Skemer⁹
Astrophysical Journal Letters 871, L3 Link to Article [DOI: 10.3847/2041-8213/aaf9b6]
¹Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA, USA
²Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
³Department of Physics and Astronomy, California State University Northridge, Northridge, CA, USA
⁴Department of Physics, Brandeis University, Waltham, MA, USA
⁵NASA Ames Research Center, Moffett Field, CA, USA
⁶SETI Institute, Mountain View, CA, USA
⁷Department of Physics, University of California, Santa Cruz, Santa Cruz, CA, USA
⁸Chabot-Las Positas Community College, Dublin, CA, USA
⁹Department of Astronomy, University of California, Santa Cruz, Santa Cruz, CA, USA

Low-mass M dwarfs represent the most common outcome of star formation, but their complex emergent spectra hinder detailed studies of their composition and initial formation. The measurement of isotopic ratios is a key tool that has been used to unlock the formation of our solar system, the Sun, and the nuclear processes within more massive stars. We observed GJ 745AB, two M dwarfs orbiting in a wide binary, with the NASA Infrared Telescope Facility/iSHELL spectrograph. Our spectroscopy of CO in these stars at the 4.7 μm fundamental and 2.3 μm first-overtone rovibrational bandheads reveals , , and in their photospheres. Because the stars are fully convective, the atomic constituents of these isotopologues should be uniformly mixed throughout the stars’ interiors. We find that in these M dwarfs, both / and / greatly exceed the Solar values. These measurements cannot be explained solely by models of Galactic chemical evolution, but require that the stars formed from an interstellar medium significantly enriched by material ejected from an exploding core-collapse supernova. These isotopic measurements complement the elemental abundances provided by large-scale spectroscopic surveys, and open a new window onto studies of Galactic evolution, stellar populations, and individual systems.

¹Hamed Pourkhorsandi et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13311]
¹Aix Marseille Universite, CNRS, IRD, Coll France, INRA, CEREGE, Aix-en-Provence, France
Published by arrangement with John Wiley & Sons

We present for the first time a detailed report on the discovery of a new meteorite collection region in the Lut Desert, eastern–southeastern Iran, describing its geological, morphological, and climatic setting. Our search campaigns, alongside with the activity of meteorite hunters, yielded >200 meteorite finds. Here, we report on their classification, spatial distribution, and terrestrial weathering. All the collected meteorites are ordinary chondrites (OCs). The most abundant by far are the highly weathered paired H5 distributed in the northwest of Kalut area (central Lut, Kerman dense collection area). The second are well‐preserved paired L5 also found in Kalut region. A detailed study of the geochemistry and mineralogy of selected meteorites reveals significant effects of terrestrial weathering. Fe,Ni metal (hereafter simply metal) and troilite are transformed into Fe oxyhydroxides. A rather unusual type of troilite weathering to pyrite/marcasite is observed in most of the Lut Desert meteorites. Magnetic measurements and X‐ray diffractometry confirm the occurrence of terrestrial weathering products, with the dominance of maghemite, goethite, and hematite. Mobile elements, such as Li, Sr, Mo, Ba, Tl, Th, and U, are enriched with respect to fresh falls. Meanwhile, a decrease in the V, Cr, Co, Rb (and possibly Fe) due to terrestrial weathering is detectable. The total carbon and CaCO₃ is higher than in samples from other hot deserts. The weathering effects observed in the Lut Desert OCs can be used as distinctive indicators to distinguish them from meteorites from other regions of the Earth. Measurements of terrestrial age (¹⁴C) show a range of 10–30 ka, which is in the range of ages reported for meteorites from other hot deserts except the Atacama Desert (Chile). Considering the high potential of the Lut Desert in meteorite preservation, systematic works should lead to the discovery of more samples giving access to interesting material for future studies.

Kent C. Condie^a, Charles K. Shearer^a,b
Geochimica et Cosmochimcia Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.05.027]
^aDepartment of Earth and Environmental Science, New Mexico Tech, Socorro, NM 87801, USA
^bInstitute of Meteoritics, University of New Mexico, Albuquerque, NM 87131, USA
Copyright Elsevier

Major processes affecting high field strength (HFSE) and rare earth (REE) element ratios in planetary basalts are degree of melting, separation of metal-sulfide melt fractions, addition and loss of silicate melt, ilmenite fractionation, and subduction. Fractional crystallization of planetary magma oceans has left a surviving imprint on only three bodies for which we have data: the Moon, Vesta, and the angrite parent body. Thorium mobilization in aqueous fluids may account for decoupling of Th and Nb in planetary systems, and this is especially notable on Earth but also possible on Mars, the Moon and some asteroids. On Earth, HFSE and REE ratios in young basalts characterize hydrated (HM), enriched (EM) and depleted (DM) mantle sources, associated with, respectively, subduction, mantle plumes and ocean ridges. Terrestrial hydrated and depleted mantle were in existence by at least 4 Ga and possibly they may have been produced in a stagnant lid tectonic regime before 3 Ga. Also, removal of Nb in metal-sulfide melts can force the composition of silicate restitic material into the hydrated mantle field on HFSE-REE graphs, thus not requiring hydration. Such an origin is probable for “hydrated” mantle in primitive achondrites and plutonic angrites. The record of all three types of mantle in basalts from other bodies in the Solar System indicates the three mantle reservoirs are not diagnostic of plate tectonics, but can be produced in stagnant lid settings.

Enriched mantle is thus far recognized only in Earth and possibly Mars. There are at least two enriched mantle reservoirs in Earth: a primordial (> 4 Ga) reservoir, perhaps hidden in the D” layer above the core and rarely sampled by basalts, and a recycled plate reservoir (< 3 Ga), perhaps located in the two LLSVPs commonly sampled by oceanic island basalts. Between 3 and 2 Ga, the recycled enriched mantle reservoir became established in Earth, possibly in response to the widespread propagation of subduction. On Mars enriched mantle shows depleted radiogenic isotopic signatures and requires a multistage process to decouple trace element and isotopic systems.

Although there are several processes by which Nb can be fractionated from Ta in planetary bodies, the low Nb/Ta (<15) characteristic of some planetary and asteroid basalts may reflect separation of a metal-sulfide melt enriched in Nb, which may or may not produce a core. This fractionation must occur early during a relatively reduced stage of planetary evolution (IW-3 to IW-5) such that Nb behaves as a chalcophile or siderophile element. If the average Nb/Ta ratio of both primitive and depleted mantle is equal to 15, production of basaltic magma in the terrestrial mantle through time has not fractionated Nb from Ta. On the other hand, if the Nb/Ta in primitive mantle equals 17, Nb must be fractionated from Ta before 4 Ga, perhaps by partitioning into the core during or soon after planetary accretion when reducing conditions may have existed.

Darryl Seligman¹, Gregory Laughlin¹, and Konstantin Batygin²
Astrophysical Journal Letters 876, L26 Link to Article [DOI: 10.3847/2041-8213/ab0bb5]
¹Dept. of Astronomy, Yale University, New Haven, CT 06517, USA
²Division of Geological and Planetary Sciences, Caltech, Pasadena, CA 91125, USA

We show that the P ~ 8 hr photometric period and the astrometrically measured A _ng ~ 2.5 × 10⁻⁴cm s⁻² non-gravitational acceleration (at r ~ 1.4 au) of the interstellar object 1I/2017 (‘Oumuamua) can be explained by a nozzle-like venting of volatiles whose activity migrated to track the subsolar location on the object’s surface. Adopting the assumption that ‘Oumuamua was an elongated a × b × c ellipsoid, this model produces a pendulum-like rotation of the body and implies a long semi-axis . This scale agrees with the independent estimates of ‘Oumuamua’s size that stem from its measured brightness, assuming an albedo of p ~ 0.1, which is appropriate for ices that have undergone long-duration exposure to the interstellar cosmic-ray flux. Using ray tracing, we generate light curves for ellipsoidal bodies that are subject to both physically consistent subsolar torques and to the time-varying geometry of the Sun–Earth–’Oumuamua configuration. Our synthetic light curves display variations from chaotic tumbling and changing cross-sectional illumination that are consistent with the observations, while avoiding significant secular changes in the photometric periodicity. If our model is correct, ‘Oumuamua experienced mass loss that wasted ~10% of its total mass during the ~100 days span of its encounter with the inner solar system and had an icy composition with a very low [C/O]  0.003. Our interpretation of ‘Oumuamua’s behavior is consistent with the hypothesis that it was ejected from either the outer regions of a planetesimal disk after an encounter with an embedded M _p ~ M _Nep planet, or from an exo-Oort cloud.

M. A. Cordiner^1,2 et al. (>10)
Astrophysical Journal Letters 8709, L26 Link to Article [DOI: 10.3847/2041-8213/aafb05]
¹NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
²Department of Physics, Catholic University of America, Washington, DC 20064, USA

The Atacama Large Millimeter/submillimeter Array (ALMA) is a powerful tool for high-resolution mapping of comets, but the main interferometer (comprised of 50 × 12 m antennas) is insensitive to the largest coma scales due to a lack of very short baselines. In this Letter, we present a new technique employing ALMA autocorrelation data (obtained simultaneously with the interferometric observations), effectively treating the entire 12 m array as a collection of single-dish telescopes. Using combined autocorrelation spectra from 28 active antennas, we recovered extended HCN coma emission from comet C/2012 S1 (ISON), resulting in a fourteen-fold increase in detected line brightness compared with the interferometer. This resulted in the first detection of rotational emission from H¹³CN in this comet. Using a detailed coma radiative transfer model accounting for optical depth and non-local thermodynamic equilibrium excitation effects, we obtained an H¹²CN/H¹³CN ratio of 88 ± 18, which matches the terrestrial value of 89. This is consistent with a lack of isotopic fractionation in HCN during comet formation in the protosolar accretion disk. The possibility of future discoveries in extended sources using autocorrelation spectroscopy from the main ALMA array is thus demonstrated.

Christopher Spalding
Astrophysical Journal Letters 869, L17 Link to Article [DOI: 10.3847/2041-8213/aaf478]
Department of Astronomy, Yale University, New Haven, CT 06511, USA

Our solar system is almost entirely devoid of material interior to Mercury’s orbit, in sharp contrast to the multiple Earth masses of material commonly residing within the analogous region of extrasolar planetary systems. Recent work has suggested that Jupiter’s orbital migration early in the solar system’s history fragmented primordial planetary material within the inner solar system. However, the reason for the absence of subsequent planet formation within 0.4 au remains unsolved. Here, we show that leftover debris interior to Mercury’s current orbit was susceptible to outward migration driven by the early Solar wind, enhanced by the Sun’s primordial rapid rotation and strong magnetic field. The ram pressure arising from azimuthal motion of the Solar wind plasma transported ~100 m-sized objects and smaller from 0.1 au out to the terrestrial planet-forming zone within the suspected ~30–50 Myr timespan of the Earth’s formation. The mass of material within this size class typically exceeds Mercury, and can rival that of Earth. Consequently, the present-day region of terrestrial planets and the asteroid belt has been supplied by a large mass of material from the innermost, hot solar system, providing a potential explanation for the evidence of high-temperature alteration within some asteroids and the high iron content of Mercury.

Gerrit Budde, Christoph Burkhardt & Thorsten Kleine
Nature Astronomy Link to Article [https://www.nature.com/articles/s41550-019-0779-y]
Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany

Earth grew through collisions with Moon-sized to Mars-sized planetary embryos from the inner Solar System, but it also accreted material from greater heliocentric distances^1,2, including carbonaceous chondrite-like bodies, the likely source of Earth’s water and highly volatile species^3,4. Understanding when and how this material was added to Earth is critical for constraining the dynamics of terrestrial planet formation and the fundamental processes by which Earth became habitable. However, earlier studies inferred very different timescales for the delivery of carbonaceous chondrite-like bodies, depending on assumptions about the nature of Earth’s building materials^{5,6,7,8,9,10,11}. Here we show that the Mo isotopic composition of Earth’s primitive mantle falls between those of the non-carbonaceous and carbonaceous reservoirs^12,13,14,15, and that this observation allows us to quantify the accretion of carbonaceous chondrite-like material to Earth independently of assumptions about its building blocks. As most of the Mo in the primitive mantle was delivered by late-stage impactors¹⁰, our data demonstrate that Earth accreted carbonaceous bodies late in its growth history, probably through the Moon-forming impact. This late delivery of carbonaceous material probably resulted from an orbital instability of the gas giant planets, and it demonstrates that Earth’s habitability is strongly tied to the very late stages of its growth.