J. ORM€O1, P. MINDE², A. T. NIELSEN³, and C. ALWMARK⁴
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13275]
¹Centro de Astrobiologıa (INTA-CSIC), ES-28850 Torrejon de Ardoz, Spain
²Bj€orkv€agen 28, SE-98336, Malmberget
³Department of Geosciences and Natural Resource Management, University of Copenhagen, DK-1350 Copenhagen, Denmark
⁴Department of Geology, Lund University, SE-22362 Lund, Sweden
Published by arrangement with John Wiley & Sons

The lower Cambrian Vakkejokk Breccia is a proximal ejecta layer from a shallow marine impact. It is exposed for ~7 km along a steep mountainside in Lapland, northernmost Sweden. In its central parts, the layer is up to ~27 m thick. Here the breccia shows a vertical differentiation into (1) a lower subunit consisting of strongly deformed target sediments mixed with up to decameter size, mainly crystalline basement clasts (i.e., lower polymict breccia [LPB]); (2) a middle subunit consisting of a polymict, blocky to gravelly breccia, commonly graded (i.e., graded polymict breccia [GPB]), that, in turn, is sporadically overlain by (3) a few dm thick, sandy bed (i.e., top sandstone [TS]). Previous work interpreted the graded beds as deposited by resurging water during early crater modification. We made three short (<1.35 m) core drillings through the graded beds. The line‐logging technique previously used on cores from other marine‐target craters was complemented by logging of equal‐sized cells in photos made along the cores. Granulometry and clast lithology determinations provide further evidence for the top beds of the breccia being resurge deposits. However, the magnitude of this resurge can only be assessed by future deep core drilling of the infill of the crater hidden below the mountain.

Tetsuya Komabayashi^a, Giacomo Pesce^a, Ryosuke Sinmyo^b, Takaaki Kawazoe^c, Helene Breton^a, Yuta Shimoyama^d, Konstantin Glazyrin^e, Zuzana Konôpková^e, Mohamed Mezouar^f
Earth and Planetary Science Letters 511, 12-24 Link to Article [https://doi.org/10.1016/j.epsl.2019.01.056]
^aSchool of Geo Sciences and Centre for Science at Extreme Conditions, University of Edinburgh,EH93FE,UK
^bBayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany
^cDepartment of Earth and Planetary Systems Science, Hiroshima University, Hiroshima, Japan
^dDepartment of Earth and Space Science, Osaka University, Osaka, Japan
^eDeutsches Elektronen-Synchrotron(DESY), Photon Science, Notekstrasse 85, 22607 Hamburg, Germany
^fEuropean SynchrotronRadiation Facility, BP220, F-38043 Grenoble Cedex, France
Copyright Elsevier

Phase relations in Fe–5 wt%Ni–4 wt%Si alloy was examined in an internally resistive heated diamond anvil cell under high pressure (P) and temperature (T) conditions to about 200 GPa and 3900 K by in-situ synchrotron X-ray diffraction. The hexagonal close-packed (hcp) structure was observed to the highest P–T condition, supporting the idea that the stable iron alloy structure in Earth’s inner core is hcp. The P–Tlocations of the phase transition between the face-centred cubic (fcc) and hcp structures were also constrained to 106 GPa. The transition occurs at 15 GPa and 1000 K similar to for pure Fe. The Clausius–Clapeyron slope is however, 0.0480 GPa/K which is larger than reported slopes for Fe (0.0394 GPa/K), Fe–9.7 wt%Ni (0.0426 GPa/K), and Fe–4 wt%Si (0.0394 GPa/K), stabilising the fcc structure towards high pressure. Thus the simultaneous addition of Ni and Si to Fe increases the dP/dT slope of the fcc–hcp transition. This is associated with a small volume change upon transition in Fe–Ni–Si. The triple point, where the fcc, hcp, and liquid phases coexist in Fe–5 wt%Ni–4 wt%Si is placed at 145 GPa and 3750 K. The resulting melting temperature of the hcp phase at the inner core-outer core boundary lies at 550 K lower than in pure Fe.

Zh. Wang (王兆鹏) and M. Cuntz
Astrophysical Journal 873, 113 Link to Article [DOI: 10.3847/1538-4357/ab0377 ]
Department of Physics University of Texas at Arlington, Arlington, TX 76019-0059, USA

In Papers I and II, a comprehensive approach was utilized for the calculation of S-type and P-type habitable regions in stellar binary systems for both circular and elliptical orbits of the binary components. This approach considered a joint constraint, including orbital stability for possible system planets and a habitable region, determined by the stellar radiative energy fluxes (“radiative habitable zone”; RHZ). Specifically, the stellar S-type and P-type RHZs are calculated based on the solution of a fourth-order polynomial. However, in concurrent developments, mostly during 2013 and 2014, important improvements have been made in the computation of stellar habitable zones for single stars based on updated climate models given by R. K. Kopparapu and collaborators. These models entail considerable changes for the inner and outer limits of the stellar habitable zones. Moreover, regarding the habitability limit given by the runaway greenhouse effect, notable disparities were identified between Earth, Mars, and super-Earth planets due to differences in their atmospheric models, thus affecting their potential for habitability. It is the aim of this study to compute S-type and P-type habitable regions of binaries in response to the updated planetary models. Moreover, our study will also consider improved relationships between effective temperatures, radii, and masses for low-luminosity stars.

N. G. RUDRASWAMI¹, Yves MARROCCHI², M. SHYAM PRASAD¹, D. FERNANDES¹,Johan VILLENEUVE², and S. TAYLOR³
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13281]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403004, India
²CRPG, CNRS, Universite de Lorraine, UMR 7358, Vandoeuvre-les-Nancy F-54501, France
³Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire 03755–1290, USA
Published by arrangement with John Wiley & Sons

We identified 66 chromite grains from 42 of ~5000 micrometeorites collected from Indian Ocean deep‐sea sediments and the South Pole water well. To determine the chromite grains precursors and their contribution to the micrometeorite flux, we combined quantitative electron microprobe analyses and oxygen isotopic analyses by high‐resolution secondary ion mass spectrometry. Micrometeorite chromite grains show variable O isotopic compositions with δ¹⁸O values ranging from −0.8 to 6.0‰, δ¹⁷O values from 0.3 to 3.6‰, and Δ¹⁷O values from −0.9 to 1.6‰, most of them being similar to those of chromites from ordinary chondrites. The oxygen isotopic compositions of olivine, considered as a proxy of chromite in chromite‐bearing micrometeorites where chromite is too small to be measured in ion microprobe have Δ¹⁷O values suggesting a principal relationship to ordinary chondrites with some having carbonaceous chondrite precursors. Furthermore, the chemical compositions of chromites in micrometeorites are close to those reported for ordinary chondrite chromites, but some contribution from carbonaceous chondrites cannot be ruled out. Consequently, carbonaceous chondrites cannot be a major contributor of chromite‐bearing micrometeorites. Based on their oxygen isotopic and elemental compositions, we thus conclude with no ambiguity that chromite‐bearing micrometeorites are largely related to fragments of ordinary chondrites with a small fraction from carbonaceous chondrites, unlike other micrometeorites deriving largely from carbonaceous chondrites.

Ozan UNSALAN1,2 et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13258]
¹University of Istanbul, 34134 Vezneciler, Fatih Istanbul, Turkey
²Ege University, 35100, Bornova, Izmir, Turkey
Published by arrangement with John Wiley & Sons

The Sariçiçek howardite meteorite shower consisting of 343 documented stones occurred on September 2, 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Sariçiçek experienced a complex cosmic‐ray exposure history, exposed during ~12–14 Ma in a regolith near the surface of a parent asteroid, and that an ~1 m sized meteoroid was launched by an impact 22 ± 2 Ma ago to Earth (as did one‐third of all HED meteorites). SIMS dating of zircon and baddeleyite yielded 4550.4 ± 2.5 Ma and 4553 ± 8.8 Ma crystallization ages for the basaltic magma clasts. The apatite U‐Pb age of 4525 ± 17 Ma, K‐Ar age of ~3.9 Ga, and the U,Th‐He ages of 1.8 ± 0.7 and 2.6 ± 0.3 Ga are interpreted to represent thermal metamorphic and impact‐related resetting ages, respectively. Petrographic; geochemical; and O‐, Cr‐, and Ti‐isotopic studies confirm that Sariçiçek belongs to the normal clan of HED meteorites. Petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the Sariçiçek regolith and organic contamination of the meteorite after a few days on soil. Video observations of the fall show an atmospheric entry at 17.3 ± 0.8 km s⁻¹ from NW; fragmentations at 37, 33, 31, and 27 km altitude; and provide a pre‐atmospheric orbit that is the first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data indicate the similarity of Sariçiçek with the Vesta asteroid family (V‐class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of meteoroid delivery to Earth shows that the complete disruption of a ~1 km sized Vesta family asteroid or a ~10 km sized impact crater on Vesta is required to provide sufficient meteoroids ≤4 m in size to account for the influx of meteorites from this HED clan. The 16.7 km diameter Antionia impact crater on Vesta was formed on terrain of the same age as given by the ⁴He retention age of Sariçiçek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was formed ~22 Ma ago.

Quanzhi Ye (叶泉志)^1,2,3 and Mikael Granvik^4,5
Astrophysical Journal 873, 104 Link to Article [DOI: 10.3847/1538-4357/ab05ba ]
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
³Department of Physics and Astronomy, The University of Western Ontario, London, Ontario N6A 3K7, Canada
⁴Division of Space Technology, Luleå University of Technology, Box 848, SE-98128 Kiruna, Sweden
⁵Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland

The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally driven disruption may be an important process in the removal of rocky bodies in the solar system. Here we report our study of how the debris streams arise from possible thermally driven disruptions in the near-Sun region. We calculate that a small body with a diameter 0.5 km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every ~2 kyr. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approachers than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al.’s near-Earth object population model, and find that they evolve 10–70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems.

Ming-Ming Kang (康明铭)^1,2, Yang Hu (胡杨)³, Hong-Bo Hu (胡红波)^4,5, and Shou-Hua Zhu (朱守华)^6,7,8
Astrophysical Journal 873, 68 Link to Article [DOI: 10.3847/1538-4357/ab0178 ]
¹College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China
²Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China
³College of Arts and Sciences, Shanghai Maritime University, Shanghai 201306, People’s Republic of China
⁴Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
⁵University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
⁶Institute of Theoretical Physics & State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, People’s Republic of China
⁷Collaborative Innovation Center of Quantum Matter, Beijing 100871, People’s Republic of China
⁸Center for High Energy Physics, Peking University, Beijing 100871, People’s Republic of China

The discrepancy between the theoretical prediction of primordial lithium abundances and astronomical observations is called the Lithium Problem. We assume that during Big Bang Nucleosynthesis (BBN), nucleons can gain energy and deviate from thermal equilibrium, namely BBN cosmic rays (BBNCRs). BBNCR primary spectra are uncertain and the Coulomb energy-loss processes are neglected; however, we suppose a steady state of BBNCR spectra referring to the Galactic cosmic ray spectra observed today, to see constraints on BBNCRs, for example, the amount and energy range, not sticking to the explicit shape of the spectra. Such extra contributions from BBNCRs can explain the discrepancy, for both Li-7 and Li-6, and will change the deuterium abundance by only a little. The allowed parameter space of such an amount of nonthermal particles and the energy range are shown. The hypothesis is stable regardless of the cross-section uncertainty of relevant reactions and the explicit shape of the energy spectrum.

Kaori JOGO¹, Motoo ITO², Shigeru WAKITA³, Sachio KOBAYASHI², and Jong Ik LEE¹
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13272]
¹Division of Earth-System Sciences, Korea Polar Research Institute, 26 Songdomirae-ro, Yeonsu-gu, Incheon 21990,South Korea
²Kochi Institute for Core Sample Research, JAMSTEC B200 Monobe, Nankoku, Kochi 783-8502, Japan
³Center for Computational Astrophysics, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka,Tokyo 181-8588, Japan
Published by arrangement with John Wiley & Sons

We observed metamorphosed clasts in the CV3 chondrite breccias Graves Nunataks 06101, Vigarano, Roberts Massif 04143, and Yamato‐86009. These clasts are coarse‐grained polymineralic rocks composed of Ca‐bearing ferroan olivine (Fa_24–40, up to 0.6 wt% CaO), diopside (Fs_7–12Wo_44–50), plagioclase (An_52–75), Cr‐spinel (Cr/[Cr + Al] = 0.4, Fe/[Fe + Mg] = 0.7), sulfide and rare grains of Fe‐Ni metal, phosphate, and Ca‐poor pyroxene (Fs₂₄Wo₄). Most clasts have triple junctions between silicate grains. The rare earth element (REE) abundances are high in diopside (REE ~3.80–13.83 × CI) and plagioclase (Eu ~12.31–14.67 × CI) but are low in olivine (REE ~0.01–1.44 × CI) and spinel (REE ~0.25–0.49 × CI). These REE abundances are different from those of metamorphosed chondrites, primitive achondrites, and achondrites, suggesting that the clasts are not fragments of these meteorites. Similar mineralogical characteristics of the clasts with those in the Mokoia and Yamato‐86009 breccias (Jogo et al. 2012) suggest that the clasts observed in this study would also form inside the CV3 chondrite parent body. Thermal modeling suggests that in order to reach the metamorphosed temperatures of the clasts of >800 °C, the clast parent body should have accreted by ~2.5–2.6 Ma after CAIs formation. The consistency of the accretion age of the clast parent body and the CV3 chondrule formation age suggests that the clasts and CV3 chondrites could be originated from the same parent body with a peak temperature of 800–1100 °C. If the body has a peak temperature of >1100 °C, the accretion age of the body becomes older than the CV3 chondrule formation age and multiple CV3 parent bodies are likely.

Christian KOEBERL^1,2 and Ludovic FERRIERE¹
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13250]
¹Natural History Museum, Burgring 7, A-1010 Vienna, Austria
²Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
Published by arrangement with John Wiley & Sons

ibyan Desert Glass (LDG) is an enigmatic natural glass, about 28.5 million years old, which occurs on the floor of corridors between sand dunes of the southwestern corner of the Great Sand Sea in western Egypt, near the Libyan border. The glass occurs as centimeter‐ to decimeter‐sized, irregularly shaped, and strongly wind‐eroded pieces. The origin of the LDG has been the subject of much debate since its discovery, and a variety of exotic processes were suggested, including a hydrothermal sol‐gel process or a lunar volcanic source. However, evidence of an impact origin of these glasses included the presence of schlieren and partly or completely digested minerals, such as lechatelierite, baddeleyite (a high‐T breakdown product of zircon), and the presence of a meteoritic component in some of the glass samples. The source material of the glass remains an open question. Geochemical data indicate that neither the local sands nor sandstones from various sources in the region are good candidates to be the sole precursors of the LDG. No detailed studies of all local rocks exist, though. There are some chemical and isotopic similarity to rocks from the BP and Oasis impact structures in Libya, but no further evidence for a link between these structures and LDG was found so far. These complications and the lack of a crater structure in the area of the LDG strewn field have rendered an origin by airburst‐induced melting of surface rocks as a much‐discussed alternative. About 20 years ago, a few shocked quartz‐bearing breccias (float samples) were found in the LDG strewn field. To study this question further, several basement rock outcrops in the LDG area were sampled during three expeditions in the area. Here we report on the discovery of shock‐produced planar microdeformation features, namely planar fractures (PFs), planar deformation features (PDFs), and feather features (FFs), in quartz grains from bedrock samples. Our observations show that the investigated samples were shocked to moderate pressure, of at least 16 GPa. We interpret these observations to indicate that there was a physical impact event, not just an airburst, and that the crater has been almost completely eroded since its formation.

Stephen M.Elardo^a,b, Anat Shahar^a, Timothy D. Mock^c, Corliss K. Sio^a,d
Earth and Planetary Science Letters 511, 12-24 Link to Article [https://doi.org/10.1016/j.epsl.2019.02.025]
^aGeophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA
^bDepartment of Geological Sciences, University of Florida, Gainesville, FL 32611, USA
^cDepartment of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA
^dNuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
Copyright Elsevier

We have conducted high-pressure, high-temperature isotope exchange experiments between molten silicate and molten Fe–Si–C-alloys to constrain the effect of Si on equilibrium Fe isotope fractionation during planetary core formation. The values of <span id="MathJax-Element-1-Frame" class="MathJax_SVG" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 16.200000762939453px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="Δ57″>Fe_{Metal-Silicate} at 1850 °C and 1 GPa determined by high-resolution MC-ICP-MS in this study range from <span id="MathJax-Element-2-Frame" class="MathJax_SVG" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 16.200000762939453px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="−0.013±0.054‰”>‰ (2SE) to 0.072 ± 0.085‰ with 1.34–8.14 atom % Si in the alloy, respectively. These results, although not definitive on their own, are consistent with previous experimental results from our group and a model in which elements that substitute for Fe atoms in the alloy structure (i.e., Ni, S, and Si) induce a fractionation of Fe isotopes between molten silicate and molten Fe-alloys during planetary differentiation. Using in situ synchrotron X-ray diffraction data for molten Fe-rich alloys from the literature, we propose a model to explain this fractionation behavior in which impurity elements in Fe-alloys cause the nearest neighbor atomic distances to shorten, thereby stiffening metallic bonds and increasing the preference of the alloy for heavy Fe isotopes relative to the silicate melt. This fractionation results in the bulk silicate mantles of the smaller terrestrial planets and asteroids becoming isotopically light relative to chondrites, with an enrichment of heavy Fe isotopes in their cores, consistent with magmatic iron meteorite compositions. Our model predicts a bulk silicate mantle <span id="MathJax-Element-3-Frame" class="MathJax_SVG" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 16.200000762939453px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="δ57″>Fe ranging from −0.01‰ to −0.12‰ for the Moon, −0.06‰ to −0.33‰ for Mars, and −0.08‰ to −0.33‰ for Vesta. Independent estimates of the <span id="MathJax-Element-4-Frame" class="MathJax_SVG" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 16.200000762939453px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="δ57″>Fe of primitive mantle source regions that account for Fe isotope fractionation during partial melting agree well with these ranges for all three planetary bodies and suggest that Mars and Vesta have cores with impurity (i.e., Ni, S, Si) abundances near the low end of published ranges. Therefore, we favor a model in which core formation results in isotopically light bulk silicate mantles for the Moon, Mars, and Vesta. The processes of magma ocean crystallization, mantle partial melting, and fractional crystallization of mantle-derived melts are all likely to result in heavy Fe isotope enrichment in the melt phase, which can explain why basaltic samples from these planetary bodies have variable <span id="MathJax-Element-5-Frame" class="MathJax_SVG" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 16.200000762939453px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0" role="presentation" data-mathml="δ57″>Fe values consistently heavier than our bulk mantle estimates. Additionally, we find no clear evidence that Fe isotopes were fractionated to a detectable level by volatile depletion processes during or after planetary accretion, although it cannot be ruled out.