^aN. Mangold (>10)*
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.11.005]

a LPG-Nantes, CNRS/Université Nantes, 44322 Nantes, France
*Find the extensive, full author and affiliation list on the publishers website
Copyright Elsevier

Rocks analyzed by the Curiosity rover in Gale crater include a variety of clastic sedimentary rocks and igneous float rocks transported by fluvial and impact processes. To facilitate the discussion of the range of lithologies, we present in this article a petrological classification framework adapting terrestrial classification schemes to Mars compositions (such as Fe abundances typically higher than for comparable lithologies on Earth), to specific Curiosity observations (such as common alkali-rich rocks), and to the capabilities of the rover instruments. Mineralogy was acquired only locally for a few drilled rocks, and so it does not suffice as a systematic classification tool, in contrast to classical terrestrial rock classification. The core of this classification involves (1) the characterization of rock texture as sedimentary, igneous or undefined according to grain/crystal sizes and shapes using imaging from the ChemCam Remote Micro-Imager (RMI), Mars Hand Lens Imager (MAHLI) and Mastcam instruments, and (2) the assignment of geochemical modifiers based on the abundances of Fe, Si, alkali, and S determined by the Alpha Particle X-ray Spectrometer (APXS) and ChemCam instruments. The aims are to help understand Gale crater geology by highlighting the various categories of rocks analyzed by the rover. Several implications are proposed from the cross-comparisons of rocks of various texture and composition, for instance between in place outcrops and float rocks. All outcrops analyzed by the rover are sedimentary; no igneous outcrops have been observed. However, some igneous rocks are clasts in conglomerates, suggesting that part of them are derived from the crater rim. The compositions of in-place sedimentary rocks contrast significantly with the compositions of igneous float rocks. While some of the differences between sedimentary rocks and igneous floats may be related to physical sorting and diagenesis of the sediments, some of the sedimentary rocks (e.g., potassic rocks) cannot be paired with any igneous rocks analyzed so far. In contrast, many float rocks, which cannot be classified from their poorly defined texture, plot on chemistry diagrams close to float rocks defined as igneous from their textures, potentially constraining their nature.

¹Lucy F. Lim, ^1,2Richard D. Starr, ^1,3Larry G. Evans, ¹Ann M. Parsons, ⁴Michael E. Zolensky, and ⁵William V. Boynton
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12786]

¹NASA Goddard Space Flight Center, Code 691, Greenbelt, Maryland 20771, USA
²Catholic University of America, Washington, District of Columbia 20064, USA
³Computer Sciences Corporation, Lanham-Seabrook, Maryland 20706, USA
⁴ARES, NASA Johnson Space Center, Houston, Texas 77058, USA
⁵Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
Published by arrangement with John Wiley & Sons

To evaluate the feasibility of measuring differences in bulk composition among carbonaceous meteorite parent bodies from an asteroid or comet orbiter, we present the results of a performance simulation of an orbital gamma-ray spectroscopy (GRS) experiment in a Dawn-like orbit around spherical model asteroids with a range of carbonaceous compositions. The orbital altitude was held equal to the asteroid radius for 4.5 months. Both the asteroid gamma-ray spectrum and the spacecraft background flux were calculated using the MCNPX Monte-Carlo code. GRS is sensitive to depths below the optical surface (to ≈20–50 cm depth depending on material density). This technique can therefore measure underlying compositions beneath a sulfur-depleted (e.g., Nittler et al. 2001) or desiccated surface layer. We find that 3σ uncertainties of under 1 wt% are achievable for H, C, O, Si, S, Fe, and Cl for five carbonaceous meteorite compositions using the heritage Mars Odyssey GRS design in a spacecraft-deck-mounted configuration at the Odyssey end-of-mission energy resolution, FWHM = 5.7 keV at 1332 keV. The calculated compositional uncertainties are smaller than the compositional differences between carbonaceous chondrite subclasses.

¹Boris Reznik, ¹Agnes Kontny, ²Jörg Fritz
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12787]

¹Division of Structural Geology and Tectonophysics, Institute of Applied Geosciences, Karlsruhe Institute of Technology,Karlsruhe, Germany
²Saalbau Weltraum Projekt, Heppenheim, Germany
Published by arrangement with John Wiley & Sons

This study demonstrates a relationship between changes of magnetic susceptibility and microstructure developing in minerals of a magnetite-bearing ore, experimentally shocked to pressures of 5, 10, 20, and 30 GPa. Shock-induced effects on magnetic properties were quantified by bulk magnetic susceptibility measurements while shock-induced microstructures were studied by high-resolution scanning electron microscopy. Microstructural changes were compared between magnetite, quartz, amphibole, and biotite grains. In the 5 GPa sample, a sharp drop of magnetic susceptibility correlates with distinct fragmentation as well as with formation of shear bands and twins in magnetite. At 10 GPa, shear bands and twins in magnetite are accompanied by droplet-shaped nanograins. In this shock pressure regime, quartz and amphibole still show intensive grain fragmentation. Twins in quartz and foam-shaped, highly porous amphibole are formed at 20 and 30 GPa. The formation of porous minerals suggests that shock heating of these mineral grains resulted in localized temperature spikes. The identified shock-induced features in magnetite strongly advise that variations in the bulk magnetic susceptibility result from cooperative grain fragmentation, plastic deformation and/or localized amorphization, and probably postshock annealing. In particular, the increasing shock heating at high pressures is assumed to be responsible for a partial defect annealing which we suggest to be responsible for the almost constant values of magnetic susceptibility above 10 GPa.

¹Stefan Loehle, ^2,3Peter Jenniskens, ⁴Hannah Böhrk, ⁵Thomas Bauer, ⁴Henning Elsäβer, ³Derek W. Sears, ⁶Michael E. Zolensky, ⁷Muawia H. Shaddad
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12788]
¹High Enthalpy Flow Diagnostics Group, Institute of Space Systems, 70569 Stuttgart, Germany
²SETI Institute, Carl Sagan Center, Mountain View, California 94043, USA
³NASA Ames Research Center, Mountain View, California 94035, USA
⁴DLR, Institute of Structures and Design, 70569 Stuttgart, Germany
⁵DLR, Institute of Technical Thermodynamics, 51147 Cologne, Germany
⁶ARES, NASA Johnson Space Center, Houston, Texas 77058, USA
⁷Physics Department, University of Khartoum, Khartoum, Sudan
Published by arrangement with John Wiley & Sons

Asteroid 2008 TC3 was characterized in a unique manner prior to impacting Earth’s atmosphere, making its October 7, 2008, impact a suitable field test for or validating the application of high-fidelity re-entry modeling to asteroid entry. The accurate modeling of the behavior of 2008 TC3during its entry in Earth’s atmosphere requires detailed information about the thermophysical properties of the asteroid’s meteoritic materials at temperatures ranging from room temperature up to the point of ablation (T ~ 1400 K). Here, we present measurements of the thermophysical properties up to these temperatures (in a 1 atm. pressure of argon) for two samples of the Almahata Sitta meteorites from asteroid 2008 TC3: a thick flat-faced ureilite suitably shaped for emissivity measurements and a thin flat-faced EL6 enstatite chondrite suitable for diffusivity measurements. Heat capacity was determined from the elemental composition and density from a 3-D laser scan of the sample. We find that the thermal conductivity of the enstatite chondrite material decreases more gradually as a function of temperature than expected, while the emissivity of the ureilitic material decreases at a rate of 9.5 × 10−5 K−1 above 770 K. The entry scenario is the result of the actual flight path being the boundary to the load the meteorite will be affected with when entering. An accurate heat load prediction depends on the thermophysical properties. Finally, based on these data, the breakup can be calculated accurately leading to a risk assessment for ground damage.

^a,bRobert C.J. Steele, ^a,cVeronika S. Heber, ^aKevin D. McKeegan
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.10.046]
^aDept. of Earth, Planetary, and Space Sciences, University of California – Los Angeles, Los Angeles, CA. 90095-1567, USA
^bNow at: Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Z ürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
^cNow at: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
Copyright Elsevier

The short-lived radionuclide ⁵³Mn decays to ⁵³CrCr providing a relative chronometer for dating the formation of Mn-rich minerals in meteorites. Secondary ion mass spectrometry (SIMS) has been extensively used for in situ dating of meteoritic olivine and carbonate by the ⁵³Mn–⁵³Cr system, however a significant analytical challenge has been realising accurate measurements of the Mn/Cr ratio in individual minerals of differing chemical compositions. During Secondary ion mass spectrometry (SIMS) analysis, elements are ionised with differing efficiencies and standard materials are required to calibrate measured ion intensities in terms of relative elemental concentrations. The carbonate system presents a particular analytical difficulty since such standards are not naturally available due to low and variable Cr contents. Here, we utilise ion implantation of Cr into carbonate and other phases to accurately determine the relative sensitivity factors of Mn/Cr during Secondary ion mass spectrometry (SIMS) analysis. We find significant variations in Mn/Cr RSF values among different carbonate minerals that depend systematically on chemical composition and we propose an empirical correction scheme that quantitatively yields an accurate RSF for carbonates of diverse chemical compositions. Correction of previous Secondary ion mass spectrometry (SIMS) carbonate data for this strong matrix effect may help to reconcile some outstanding problems regarding the timescales of aqueous alteration processes in carbonaceous chondrites. Mn-Cr ages, revised based our new understanding of the matrix effect, are, in general, earlier than previously thought and the duration of carbonate formation is shorter.

¹J.N. Connelly, ¹J. Bollard, ¹M. Bizzarro
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.10.044]
¹Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
Copyright Elsevier

Of the long-lived chronometric systems, only the dual decay of 238U and 235U to 206Pb and 207Pb, respectively, have appropriate half-lives to resolve the ages of meteorites and their components formed in the first 5 Myr of the Solar System. This paper reviews the theory and methods behind this chronometer, offers criteria to critically evaluate Pb-Pb ages and presents a summary of the current state and immediate future of the chronometry of the early Solar System. We recognize that there is some debate over the age of the Solar System, but conclude that an age of 4567.30±0.16 Ma based on four CAIs dated individually by the same method in two different laboratories is presently the best constrained published value. We further conclude that nebular chondrules dated by the Pb-Pb method require that they formed contemporaneously with CAIs and continued to form for at least ∼4 Myr, a conclusion that implies heterogeneous distribution of the short-lived 26Al nuclide in the protoplanetary disk. Planetesimals were already forming by ∼1 Myr after CAI formation, consistent with their growth predominantly through the accretion of chondrules. Nebular chondrules formation was completed by ∼5 Myr after CAI formation when the impact-generated Cba chondrules formed after the disk was cleared of gas and dust. We note that the absolute age of the Solar System or any single early Solar System object is not fundamental to any significant scientific question and that it is important only to know the correct relative ages of objects being used to piece together the formation history of the Solar System. As such, we point out the risks inherent in comparing Pb-Pb ages produced by different approaches in different laboratories at the level of the internal errors of individual ages. Until a cross-calibration exercise using synthetic and natural standards establishes the reproducibility between laboratories, only ages from a single laboratory, or between laboratories having demonstrated concordance, can provide a reliable relative chronometric framework for the formation and evolution of the early Solar System.

¹A. Ciaravella, ¹C. Cecchi-Pestellini, ²Y.-J. Chen, ³G. M. Muñoz Caro, ²C.-H. Huang, ¹A. Jiménez-Escobar, ⁴A. M. Venezia
Astrophysical Journal 828, 29 Link to Article [http://dx.doi.org/10.3847/0004-637X/828/1/29]
¹INAF—Osservatorio Astronomico di Palermo, P.za Parlamento 1, I-90134 Palermo, Italy
²Department of Physics, National Central University, Jhongli City, Taoyuan County 32054, Taiwan
³Centro de Astrobiología (INTA-CSIC), Carretera de Ajalvir, km 4, Torrejón de Ardoz, E-28850 Madrid, Spain
⁴ISMN—CNR, Via Ugo La Malfa 153, I-90146 Palermo, Italy

The processing of energetic photons on bare silicate grains was simulated experimentally on silicate films submitted to soft X-rays of energies up to 1.25 keV. The silicate material was prepared by means of a microwave assisted sol–gel technique. Its chemical composition reflects the Mg2SiO4 stoichiometry with residual impurities due to the synthesis method. The experiments were performed using the spherical grating monochromator beamline at the National Synchrotron Radiation Research Center in Taiwan. We found that soft X-ray irradiation induces structural changes that can be interpreted as an amorphization of the processed silicate material. The present results may have relevant implications in the evolution of silicate materials in X-ray-irradiated protoplanetary disks.

¹Brian J. Fry, ¹Brian D. Fields, ²John R. Ellis
Astrophysical Journal 827, 48 Link to Article [http://dx.doi.org/10.3847/0004-637X/827/1/48]
¹Department of Astronomy, University of Illinois, Urbana, IL 61801, USA
²Theoretical Physics and Cosmology Group, Department of Physics, King’s College London, London WC2R 2LS, UK; Theory Department, CERN, CH-1211 Geneva 23, Switzerland

Several searches have found evidence of ${}^{60}{\rm{Fe}}$ deposition, presumably from a near-Earth supernova (SN), with concentrations that vary in different locations on Earth. This paper examines various influences on the path of interstellar dust carrying ${}^{60}{\rm{Fe}}$ from an SN through the heliosphere, with the aim of estimating the final global distribution on the ocean floor. We study the influences of magnetic fields, angle of arrival, wind, and ocean cycling of SN material on the concentrations at different locations. We find that the passage of SN material through the mesosphere/lower thermosphere has the greatest influence on the final global distribution, with ocean cycling causing lesser alteration as the SN material sinks to the ocean floor. SN distance estimates in previous works that assumed a uniform distribution are a good approximation. Including the effects on surface distributions, we estimate a distance of ${46}_{-6}^{+10}$ pc for an $8\mbox{–}10\ {M}_{\odot }$ SN progenitor. This is consistent with an SN occurring within the Tuc-Hor stellar group ~2.8 Myr ago, with SN material arriving on Earth ~2.2 Myr ago. We note that the SN dust retains directional information to within 1◦ through its arrival in the inner solar system, so that SN debris deposition on inert bodies such as the Moon will be anisotropic, and thus could in principle be used to infer directional information. In particular, we predict that existing lunar samples should show measurable ${}^{60}{\rm{Fe}}$ differences.

^1,2Rhian H. Jones, ^2,3,4Francis M. Mccubbin, ⁵Yunbin Guan
American Mineralogist 101, 2452-2467 Link to Article [DOI: 10.2138/am-2016-5728DOI: 10.2138/am-2016-5728]
¹School of Earth and Environmental Sciences, The University of Manchester, Manchester M13 9PL, U.K.
²Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.
³Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico 87131, U.S.A.
⁴NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, Texas 77058, U.S.A.
⁵Division of Geological and Planetary Sciences, Caltech, Pasadena, California 91125, U.S.A.
Copyright: The Mineralogical Society of America

Phosphate minerals in ordinary chondrites provide a record of fluids that were present during metamorphic heating of the chondrite parent asteroids. We have carried out a petrographic study of the phosphate minerals, merrillite and apatite, in metamorphosed H group ordinary chondrites of petrologic type 4–6, to understand development of phosphate minerals and associated fluid evolution during metamorphism. In unbrecciated chondrites, apatite is Cl rich and shows textural evolution from fine-grained apatite-merrillite assemblages in type 4 toward larger, uniform grains in type 6. The Cl/F ratio in apatite shows a similar degree of heterogeneity in all petrologic types, and no systematic change in compositions with metamorphic grade, which suggests that compositions in each meteorite are dictated by localized conditions, possibly because of a limited fluid/rock ratio. The development of phosphate minerals in H chondrites is similar to that of L and LL chondrites, despite the fact that feldspar equilibration resulting from albitization is complete in H4 chondrites but not in L4 or LL4 chondrites. This suggests that albitization took place during an earlier period of the metamorphic history than that recorded by preserved apatite compositions, and chemical equilibrium was not achieved throughout the H chondrite parent body or bodies during the late stages of metamorphism. A relict igneous clast in the H5 chondrite, Oro Grande has apatite rims on relict phenocrysts of (possibly) diopside that have equilibrated with the host chondrite. Apatite in the Zag H3–6 regolith breccia records a complex fluid history, which is likely related to the presence of halite in this meteorite. The porous dark H4 matrix of Zag, where halite is observed, has a high apatite/merrillite ratio, and apatite is extremely Cl rich. One light H6 clast contains similarly Cl-rich apatite. In a second light H6 clast, apatite compositions are very heterogeneous and more F-rich. Apatites in both H4 matrix and H6 clasts have very low H2O contents. Heterogeneous apatite compositions in Zag record multiple stages of regolith processing and shock at the surface of the H chondrite parent body, and apatite records either the passage of fluids of variable compositions resulting from different impact-related processes, or the passage of a single fluid whose composition evolved as it interacted with the chondrite regolith. Unraveling the history of apatite can potentially help to interpret the internal structure of chondrite parent bodies, with implications for physical and mechanical properties of chondritic asteroids. The behavior of halogens recorded by apatite is important for understanding the behavior of volatile elements in general: if impact-melt materials close to the surface of a chondritic asteroid are readily degassed, the volatile inventories of terrestrial planets could be considerably more depleted than the CI carbonaceous chondrite abundances that are commonly assumed.

¹Kazuhide Nagashima, ¹Alexander N. Krot, ²Mutsumi Komatsu
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://dx.doi.org/10.1016/j.gca.2016.10.030]
¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean, Science and Technology, University of Hawai‘i at Mānoa, Honolulu, HI 96826, USA.
²Center for the Promotion of Advanced Study, The Graduate University for Advanced Studies, Hayama, Kanagawa, Japan.
Copyright Elsevier

We report the mineralogy, petrography, and in situ measured 26Al-26Mg systematics in chondrules from the least metamorphosed CV3 (Vigarano-type) chondrites, Kaba and Yamato (Y) 980145. Two Y 980145 chondrules measured show no resolvable excesses in 26Mg (26Mg∗), a decay product of a short-lived (t1/2 ∼0.7 Ma) radionuclide 26Al. Plagioclase in one of the chondrules is replaced by nepheline, indicative of thermal metamorphism. The lack of 26Mg∗ in the Y 980145 chondrules is most likely due to disturbance of their 26Al-26Mg systematics during the metamorphism. Although Kaba experienced extensive metasomatic alteration (<300°C), it largely avoided subsequent thermal metamorphism, and the 26Al-26Mg systematics of its chondrules appear to be undisturbed. All eight Kaba chondrules measured show 26Mg∗, corresponding to the initial 26Al/27Al ratios [(26Al/27Al)0] ranging from (2.9±1.7)×10−6 to (6.3±2.7)×10−6. If CV parent asteroid accreted rapidly after chondrule formation, the inferred (26Al/27Al)0 ratios in Kaba chondrules provide an upper limit on 26Al available in this asteroid at the time of its accretion. The estimated initial abundance of 26Al in the CV asteroid is too low to melt it and contradicts the existence of a molten core in this body suggested from the paleomagnetic records of Allende [Carporzen et al. (2011) Magnetic evidence for a partially differentiated carbonaceous chondrite parent body. Proc. Natl. Acad. Sci. USA108, 6386–6389] and Kaba [Gattacceca et al. (2013) More evidence for a partially differentiated CV parent body from the meteorite Kaba. Lunar Planet. Sci.44, abstract#1721].