¹Yuchen Xu, ¹Yangting Lin, ¹Jianchao Zhang, ¹Jialong Hao
The Astrophysical Journal 825, 111 Link to Article [http://dx.doi.org/10.3847/0004-637X/825/2/111]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China

Presolar graphite grains have been extensively studied, but are limited in carbonaceous chondrites, particularly in Murchison (CM2) and Orgueil (CI1), which sampled materials from the oxidizing regions in the solar nebula. Here, we report the first discovery of presolar graphite grains from the Qingzhen (EH3) enstatite chondrite which formed under a highly reducing condition. Eighteen presolar graphite grains were identified by C-isotope mapping of the low-density fraction (1.75–1.85 g cm−3) from Qingzhen acid residue. Another 58 graphite spherules were found in different areas of the same sample mount using a scanning electron microscope and were classified into three morphologies, including cauliflower, onion, and cauliflower–onion. The Raman spectra of these spherules vary from ordered, disordered, and glassy to kerogen-like, suggestive of a wide range of thermal metamorphisms. NanoSIMS analysis of the C- and Si-isotopes of these graphite spherules confirmed 23 presolar grains. The other 35 graphite spherules have no significant isotopic anomalies, but they share similar morphologies and Raman spectra with the presolar ones. Another three grains were identified during NanoSIMS analysis. Of all the 44 presolar graphite grains identified, six grains show 28Si-excesses, suggestive of supernovae origins, and four grains are 12C- and 29,30Si-rich, consistent with low-metallicity asymptotic giant branch star origins. Another two graphite spherules have extremely low 12C/13C ratios with marginal solar Si-isotopes. The morphologies, Raman spectra, and C- and Si-isotopic distributions of the presolar graphite grains from the Qingzhen enstatite chondrite are similar to those of the low-density fractions from Murchison carbonaceous chondrites. This study suggests a homogeneous distribution of presolar graphite grains in the solar nebula.

¹Deborah. L. Domingue, ¹Faith Vilas, ²Teck Choo, ³Karen R. Stockstill-Cahill, ⁴Joshua T.S. Cahill, ³Amanda R. Hendrix
Icarus (in Press) Link to Article [doi:10.1016/j.icarus.2016.07.011]
¹Planetary Science Institute
²Johns Hopkins University Applied Physics Laboratory
³Planetary Science Institute, 1700 E. Fort Lowell, Suite 106, Tucson, AZ 85719-2395, USA
⁴The Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA
Copyright Elsevier

Spectrophotometric examination of the Galileo Solid State Imager (SSI) observations from the Galileo spacecraft reveal surface compositional heterogeneities in mineral compositions not related to geologic unit. These include variations in olivine and orthopyroxene content of on the order of 15% and 25%, respectively. Opaque mineral phases across the inter-ridge regions vary in quantity, but consistently modeled better with ilmenite. The macroscale fraction of metallic iron varies subtly (0-10%) in quantity and in grain size (60 – 100 μm). Color properties also vary across the inter-ridge regions, indicating variations in regolith maturity. Comparisons of near-infrared ratio-reflectance suggest changes in regolith maturity that are different from those seen on the lunar surface and asteroid 433 Eros, commensurate with Gaspra’s higher olivine content. Visible to near-infrared slopes compared to near-ultraviolet to visible slopes are indicative of a nanophase iron content of 0.01% – 0.1%. Spectral mixing modeling studies of the SSI color spectra show results consistent with the presence of both microphase (> 50 nm) and nanophase (< 50nm) size iron particulates. While the quantity of microphase and nanophase iron appears to be constant within the sample areas studied, the grain size of the microphase component varies. Agglutinates are present in some areas of the inter-ridge regions, but at low abundances (∼5%).

¹K. Righter,²M. A. Cosca,²L. E. Morgan
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12692]
¹Mailcode XI2, NASA Johnson Space Center, Houston, Texas, USA
¹U.S. Geological Survey, Denver Federal Center, Denver, Colorado, USA
Published by arrangement with John Wiley & Sons

The hornblende- and biotite-bearing R chondrite LAP 04840 is a rare kind of meteorite possibly containing outer solar system water stored during metamorphism or postshock annealing deep within an asteroid. Because little is known regarding its age and origin, we determined 40Ar/39Ar ages on hornblende-rich separates of the meteorite, and obtained plateau ages of 4340(±40) to 4380(±30) Ma. These well-defined plateau ages, coupled with evidence for postshock annealing, indicate this meteorite records an ancient shock event and subsequent annealing. The age of 4340–4380 Ma (or 4.34–4.38 Ga) for this and other previously dated R chondrites is much older than most impact events recorded by ordinary chondrites and points to an ancient event or events that predated the late heavy bombardment that is recorded in so many meteorites and lunar samples.

¹Yang Liu, ²Chi Ma, ²John R. Beckett, ¹Yang Chen, ²Yunbin Guan
Earth and Planetary Science Letters (in Press) Link to Article [doi:10.1016/j.epsl.2016.06.041]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
²Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
Copyright Elsevier

Paired martian breccia meteorites, Northwest Africa (NWA) 7034 and 7533, are the first martian rocks found to contain rare-earth-element (REE) phosphates and silicates. The most common occurrence is as clusters of anhedral monazite-(Ce) inclusions in apatite. Occasionally, zoned, irregular merrillite inclusions are also present in apatite. Monazite-bearing apatite is sometimes associated with alkali-feldspar and Fe-oxide. Apatite near merrillite and monazite generally contains more F and OH (F-rich region) than the main chlorapatite host and forms irregular boundaries with the main host. Locally, the composition of F-rich regions can reach pure fluorapatite. The chlorapatite hosts are similar in composition to isolated apatite without monazite inclusions, and to euhedral apatite in lithic clasts. The U–Th-total Pb ages of monazite in three apatite are View the MathML source1.0±0.4Ga (2σ ), View the MathML source1.1±0.5Ga (2σ ), and View the MathML source2.8±0.7Ga (2σ), confirming a martian origin. The texture and composition of monazite inclusions are mostly consistent with their formation by the dissolution of apatite and/or merrillite by fluid at elevated temperatures (>100 °C).

In NWA 7034, we observed a monazite-chevkinite-perrierite-bearing benmoreite or trachyandesite clast. Anhedral monazite and chevkinite-perrierite grains occur in a matrix of sub-micrometer REE-phases and silicates inside the clast. Monazite-(Ce) and -(Nd) and chevkinite-perrierite-(Ce) and -(Nd) display unusual La and Ce depletion relative to Sm and Nd. In addition, one xenotime-(Y)-bearing pyrite-ilmenite-zircon clast with small amounts of feldspar and augite occurs in NWA 7034. One xenotime crystal was observed at the edge of an altered zircon grain, and a cluster of xenotime crystals resides in a mixture of alteration materials. Pyrite, ilmenite, and zircon in this clast are all highly altered, zircon being the most likely source of Y and HREE now present in xenotime. The association of xenotime with zircon, low U and Th contents, and the low Yb content relative to Gd and Dy in xenotime suggest the possible formation of xenotime as a byproduct of fluid–zircon reactions.

On the basis of relatively fresh apatite grains and lithic clasts in the same samples, we propose that the fluid–rock/mineral reactions occurred in the source rocks before their inclusion in NWA 7034 and 7533. Additionally, monazite-bearing apatite and REE-mineral-bearing clasts are possibly derived from different crustal origins. Thus, our results imply the wide-occurrence of hydrothermal fluids in the martian crust at 1 Ga or older, which were probably induced by impacts or large igneous intrusions.

¹Ch. Helling, ¹G. Lee, ²I. Dobbs-Dixon, ³N. Mayne, ³D. S. Amundsen, ^1,4J. Khaimova, ¹A. A. Unger, ³J. Manners, ⁵D. Acreman,⁵C. Smith
Monthly Notices of the Royal Astronomical Society 460, 855-883 Link to Article [doi: 10.1093/mnras/stw662]
¹SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, UK
²Department of Physics, NYU Abu Dhabi, PO Box 129188, Abu Dhabi, UAE
³Physics and Astronomy, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QL, UK
⁴Brooklyn College, City University of New York, Brooklyn, NY, USA
⁵Met Office, Exeter EX1 3PB, UK

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

^1,2Marianna Mészáros et al. (>10)*
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12693]
¹Space Research and Planetary Sciences, University of Bern, Bern, Switzerland
²Natural History Museum Bern, Bern, Switzerland
*Find the extensive, full author and affiliation list on the publishers website
Published by arrangement with John Wiley & Sons

Abar al’ Uj (AaU) 012 is a clast-rich, vesicular impact-melt (IM) breccia, composed of lithic and mineral clasts set in a very fine-grained and well-crystallized matrix. It is a typical feldspathic lunar meteorite, most likely originating from the lunar farside. Bulk composition (31.0 wt% Al2O3, 3.85 wt% FeO) is close to the mean of feldspathic lunar meteorites and Apollo FAN-suite rocks. The low concentration of incompatible trace elements (0.39 ppm Th, 0.13 ppm U) reflects the absence of a significant KREEP component. Plagioclase is highly anorthitic with a mean of An96.9Ab3.0Or0.1. Bulk rock Mg# is 63 and molar FeO/MnO is 76. The terrestrial age of the meteorite is 33.4 ± 5.2 kyr. AaU 012 contains a ~1.4 × 1.5 mm2 exotic clast different from the lithic clast population which is dominated by clasts of anorthosite breccias. Bulk composition and presence of relatively large vesicles indicate that the clast was most probably formed by an impact into a precursor having nonmare igneous origin most likely related to the rare alkali-suite rocks. The IM clast is mainly composed of clinopyroxenes, contains a significant amount of cristobalite (9.0 vol%), and has a microcrystalline mesostasis. Although the clast shows similarities in texture and modal mineral abundances with some Apollo pigeonite basalts, it has lower FeO and higher SiO2 than any mare basalt. It also has higher FeO and lower Al2O3 than rocks from the FAN- or Mg-suite. Its lower Mg# (59) compared to Mg-suite rocks also excludes a relationship with these types of lunar material.

¹Andrew Steele,²Francis M. McCubbin,¹Marc D. Fries
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12670]
¹Geophysical Laboratory, Carnegie Institution of Washington, NW Washington, District of Columbia, USA
²NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

This review is intended to summarize the current observations of reduced carbon in Martian meteorites, differentiating between terrestrial contamination and carbon that is indigenous to Mars. Indeed, the identification of Martian organic matter is among the highest priority targets for robotic spacecraft missions in the next decade, including the Mars Science Laboratory and Mars 2020. Organic carbon compounds are essential building blocks of terrestrial life, so the occurrence and origin (biotic or abiotic) of organic compounds on Mars is of great significance; however, not all forms of reduced carbon are conducive to biological systems. This paper discusses the significance of reduced organic carbon (including methane) in Martian geological and astrobiological systems. Specifically, it summarizes current thinking on the nature, sources, and sinks of Martian organic carbon, a key component to Martian habitability. Based on this compilation, reduced organic carbon on Mars, including detections of methane in the Martian atmosphere, is best described through a combination of abiotic organic synthesis on Mars and infall of extraterrestrial carbonaceous material. Although conclusive signs of Martian life have yet to be revealed, we have developed a strategy for life detection on Mars that can be utilized in future life-detection studies.

¹Kai Wünnemann,^1,2Meng-Hua Zhu,¹Dieter Stöffler
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12710]
¹Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Berlin, Germany
²Space Science Institute, Macau University of Science and Technology, Taipa, Macau
Published by arrangement with John Wiley & Sons

We investigated the ejection mechanics by a complementary approach of cratering experiments, including the microscopic analysis of material sampled from these experiments, and 2-D numerical modeling of vertical impacts. The study is based on cratering experiments in quartz sand targets performed at the NASA Ames Vertical Gun Range. In these experiments, the preimpact location in the target and the final position of ejecta was determined by using color-coded sand and a catcher system for the ejecta. The results were compared with numerical simulations of the cratering and ejection process to validate the iSALE shock physics code. In turn the models provide further details on the ejection velocities and angles. We quantify the general assumption that ejecta thickness decreases with distance according to a power-law and that the relative proportion of shocked material in the ejecta increase with distance. We distinguish three types of shock metamorphic particles (1) melt particles, (2) shock lithified aggregates, and (3) shock-comminuted grains. The agreement between experiment and model was excellent, which provides confidence that the models can predict ejection angles, velocities, and the degree of shock loading of material expelled from a crater accurately if impact parameters such as impact velocity, impactor size, and gravity are varied beyond the experimental limitations. This study is relevant for a quantitative assessment of impact gardening on planetary surfaces and the evolution of regolith layers on atmosphereless bodies.

^1,2Louise Alexander,^2,3Joshua F. Snape,⁴Katherine H. Joy,^1,2Hilary Downes,^1,2Ian A. Crawford
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12689]
¹Department of Earth and Planetary Science, Birkbeck College, University of London, London, UK
²The Centre for Planetary Sciences at UCL-Birkbeck, London, UK
³Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
⁴School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
Published by arrangement with John Wiley & Sons

¹Rebecca Winkler,¹Michael H. Poelchau,²Stefan Moser,¹Thomas Kenkmann
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12694]
¹Institute of Earth and Environmental Sciences—Geology, Albert-Ludwigs-Universität Freiburg (ALU), Freiburg, Germany
²Fraunhofer Institute for High-Speed Dynamics, Ernst-Mach Institut, EMI, Efringen-Kirchen, Germany
Published by arrangement with John Wiley & Sons

Hypervelocity impact experiments on porous tuff targets were carried out to determine the effect of porosity on deformation mechanisms in the crater’s subsurface. Blocks of Weibern Tuff with about 43% porosity were impacted by 2.5 mm and 12.0 mm diameter steel spheres with velocities between 4.8 km s−1 and 5.6 km s−1. The postimpact subsurface damage was quantified with computer tomography as well as with meso- and microscale analyses of the bisected crater subsurface. The intensity and style of deformation in mineral clasts and the tuff matrix were mapped and their decay with subsurface depth was determined. Subsurface deformation styles include pore space compaction, clast rotation, as well as microfracture formation. Evaluation of the deformation indicates near-surface energy coupling at a calculated depth of burial of ~2 projectile diameters (dp), which is in conflict with the crater shape, which displays a deep, central penetration tube. Subsurface damage extends to ~2 dp beneath the crater floor in the experiments with 2.5 mm projectiles and increases to ~3 dp for 12 mm projectiles. Based on overprinting relationships and the geometrical orientation of deformation features, a sequence of subsurface deformation events was derived (1) matrix compaction, (2) intragranular crack formation in clasts, (3) deformation band formation in the compacted matrix, (4) tensile fracturing.