¹Estelle Déau, ¹Linda J. Spilker, ²Alberto Flandes
¹NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91109 CA United States
²Ciencias Espaciales, Instituto de Geofísica, Universidad Nacional Autónoma de México, México, D.F., C.P. 04510, México

We investigate connections between the opposition phase curves and the spectra from ultraviolet to near infrared wavelengths of stony meteorites. We use two datasets: the reflectance dataset of Capaccioni et al., 1990 (Icarus, 83, 325), which consists of optical phase curves (from 2 to 45°) of 17 stony meteorites (3 carbonaceous chondrites, 11 ordinary chondrites, and 3 achondrites), and the spectral dataset from the RELAB database consisting of near-ultraviolet to near-infrared spectra of the same meteorites. We re-analyzed the first dataset and fit it with two morphological models to derive the amplitude A, the angular width HWHM of the surge and the slope S of the linear part. Our re-analysis confirms that stony meteorites have a non-monotonic behavior of the surge amplitude with albedo, which is also observed in planetary surfaces (Déau et al. 2013, Icarus, 226, 1465), laboratory samples (Nelson et al., 2004, Proc. Lunar Sci. Conf. 35, p. 1089) and asteroids (Belskaya and Shevchenko, 2000, Icarus, 147, 94). We find a very strong correlation between the opposition effect morphological parameters and the slope of the spectra between 0.75 μm and 0.95 μm. In particular, we found that meteorites with a positive amplitude-albedo correlation have a positive spectral slope between 0.75 μm and 0.95 μm, while meteorites with a negative amplitude-albedo correlation have a negative spectral slope between 0.75 μm and 0.95 μm. We have ruled out the role of the meteorite samples’ macro-properties (grain size, porosity and macroscopic roughness) in the correlations found because these properties were constant during the preparation of the samples. If this hypothesis is correct, this implies that other properties like the composition or the micro-properties (grain inclusions, grain shape or microscopic roughness) could have a preponderant role in the non-monotonic behavior of the surge morphology with albedo at small and moderate phase angles. Further accurate characterization of carbonaceous chrondrites samples are necessary to draw conclusions about the role of the micro-properties.

Reference
Déau E, Spilker LJ, Flandes A (2016) Re-analysis of previous laboratory phase curves: 2. Connections between opposition effect morphology and spectral features of stony meteorites. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.035]
Copyright Elsevier

¹Jaesub Hong, ²Suzanne Romaine and The MiXO team
¹Harvard University, 60 Garden Street, Cambridge 02138, MA, USA
²Smithsonian Astrophysics Observatory, 60 Garden Street, Cambridge 02138, MA, USA

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Reference
HongJ, Romaine S and The MiXO team (2016) Miniature lightweight X-ray optics (MiXO) for surface elemental composition mapping of asteroids and comets. Earth, Planets and Space 68:35
Link to Article [doi:10.1186/s40623-016-0409-1]

¹Serventi Giovanna, ²Carli Cristian, ¹Sgavetti Mariaamaria
¹Department of Physics and Earth Sciences, University of Parma, Italy
²IAPS-Inaf, Tor Vergata, Roma, Italy

Anorthositic rocks are widespread on the lunar surface and have probably been formed by flotation of PL over a magma ocean. A large portion of pristine rocks are characterized by a low Mg/(Mg+Fe) ratio, and have been classified as ferroan anorthosite, and recently, after observation from SELENE Spectral Profiler,pure anorthosites regions with more than 98% PL have been recognized.
In this paper we analyze a set of mixtures with PL content similar to the ferroan anorthosites and to the pure anorthosite regions, using the Origin Software and the Modified Gaussian Model.We consider three plagioclases with varying FeOwt% contents (PL1, PL2 and PL3)andthree mafic end-members (1)100% orthopyroxene, (2) 56% orthopyroxene and 44% clinopyroxene, and (3) 100% olivine (OL). The spectral parameters considered here are: band depth, band center, band width, c0 (the continuum intercept) and c1 (the continuum offset).
Here we have shown that in pyroxene (PX)-bearing mixtures, the PX is distinguishable even in mixtures with only 1% PX and that PX band at ca. 900 nm is always deeper than PL1 band while PL2 and PL3are deeperthan OPX 900 nm band from95, 96% PL. In OL-bearing mixtures, OL detection limit is 2% when mixed with PL1, and 3% and 4% if mixed with PL2 and PL3.
We also demonstrated how spectral parameters vary with PL%, and, generally, increasing the PL content: (1) 1250 nm band depth decreases when mixed with OL, while it deepens in mixtures with PX; (2) 1250 nm band centers generally move towards longer wavelength for PL1-bearing mixtures, while do not show significant variationsconsidering PL2/PL3-mixtures; (3)1250 nm band width of PL1 in E1 and E5-mixtures substantially widens while in other mixtures itonly slightly varies.
Here we also proposed an application to a real case, from Proclus crater, revealing how studying terrestrial analogues is fundamental to infer hypothesis on the mineralogical composition of a planetary surface, but also how the spectral convergence of spectra characterized by different compositions can led to misleading interpretations.

Reference
Giovanna S, Cristian C, Mariaamaria S (2016) Deconvolution of mixtures with high plagioclase content for the remote interpretation of lunar plagioclase-rich regions. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.020]
Copyright Elsevier

¹Jérôme Aléon
¹Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), UMR 7590, Sorbonne Universités, Museum National d’Histoire Naturelle, CNRS, UPMC, IRD, 61 rue Buffon, 75005 Paris, France

A major unanswered question in solar system formation is the origin of the oxygen isotopic dichotomy between the Sun and the planets. Individual Calcium–Aluminum-rich inclusions (CAIs) from CV chondrites exhibit almost the full isotopic range, but how their composition evolved is still unclear, which prevents robust astrochemical conclusions. A key issue is notably the yet unsolved origin of the 16O-rich isotopic composition of pyroxene in type B CAIs. Here, I report an in-situ oxygen isotope study of the archetypal type B CAI USNM-3529-Z from Allende with emphasis on the isotopic composition of pyroxene and its isotopic and petrographic relationships with other major minerals. The O isotopic composition of pyroxene is correlated with indicators of magmatic growth, indicating that the pyroxene evolved from a 16O-poor composition and became progressively enriched in 16O during its crystallization, contrary to the long held assumption that pyroxene was initially 16O-rich. This variation is well explained by isotopic exchange between a 16O-poor partial melt having the isotopic composition of melilite and a 16O-rich gas having the isotopic composition of spinel, during pyroxene crystallization.

The isotopic evolution of 3529-Z is consistent with formation in an initially 16O-rich environment where spinel and gehlenitic melilite crystallized, followed by a 16O-depletion associated with melilite partial melting and recrystallization and finally a return to the initial 16O-rich environment before pyroxene crystallization. This strongly suggests that the environment of CAI formation was globally 16O-rich, with local 16O-depletions systematically associated with high temperature events. The Al/Mg isotopic systematics of 3529-Z further indicates that this suite of isotopic changes occurred in the first 150 000 yr of the solar system, during the main CAI formation period. A new astrophysical setting is proposed, where the 16O-depletion occurs in an optically thin surface layer of the disk and may have originated by evaporation of 16O-poor interstellar dust or non-mass-dependant isotopic fractionation.

Reference
Aléon J (2016) Oxygen isotopes in the early protoplanetary disk inferred from pyroxene in a classical type B CAI. Earth and Planetary Science Letters 440, 62–70.
Link to Article [doi:10.1016/j.epsl.2016.02.007]
Copyright Elsevier

¹Frank Richter, ²Marc Chaussidon, ¹Ruslan Mendybaev, ¹Edwin Kite
¹The University of Chicago, 5734 South Ellis Avenue, Chicago, IL, 60637, U.S.A.
²Institute de Physique du Globe Paris, Sorbonne Paris Cite, UMR CNRS 7154, 1 rue Jussieu, 75005 Paris, France

Lithium concentration and isotopic fractionation profiles across augite grains from two Martian meteorites – MIL 03346 and NWA 817 – were used to determine their thermal history and implications for their geologic setting. The iron-magnesium zoning and associated magnesium isotopic fractionation of olivine grains from NWA 817 were also measured and provide a separate estimate of the cooling rate. The observed correlation of concentration with isotopic fractionation provides the essential evidence that the zoning of these grains was in fact due to diffusion and thus can be used as a measure of their cooling rate. The diffusion rate of lithium in augite depends on the oxygen fugacity, which has to be taken into account when determining a cooling rate based on the lithium zoning. The Fe-Mg exchange in olivine is much less sensitive to oxygen fugacity, but it is significantly anisotropic and for this reason we determined the direction relative to crystallographic axes of the line along which the Fe-Mg zoning was measured. We found that the cooling rate of NWA 817 determined from the lithium zoning in augite grains and that based on the Fe-Mg zoning of olivines are in good agreement at an oxygen fugacity close to that of quartz-fayalite-magnetite oxygen buffer. The cooling rate of MIL 03346 was found to be resolvably faster than that of NWA 817 – of the order of 1°C/hr for the former and of the order of 0.2°C/hr for the latter. An important observation regarding the history of MIL 03346 and NWA 817 is that the lithium and Fe-Mg zoning are only observed where the augite or olivine is in contact with the mesostasis, which implies that they were already about 80% crystallized at the time diffusion began. The augite and olivine core compositions while very homogeneous are not in equilibrium with each other, which we interpret to imply that prior to the rapid cooling there must have been a protracted period of the order of years above the solidus, during which the much faster Fe-Mg exchange in olivine compared to that in augite allowed the olivine to maintain equilibrium with a changing melt composition while the augite was not significantly affected. We suggest two possible geological settings for the origin and evolution of MIL 03346 and NWA 817: (1) A slow cooling stage in a crystallization front in a crustal magma chamber, followed by eruption of melt plus portions of the crystallization front onto the surface where the final fast cooling took place at the bottom of a lava flow or melt pond, and (2) Eruption of a crystal laden melt as a thick long-lived lava flow where the crystals continued to grow as a cumulate and were rapidly cooled when the overlying lava layer was suddenly drained.

Reference
Richter F, Chaussidon M, Mendybaev R, Kite E (2016) Reassessing the Cooling Rate and Geologic Setting of Martian Meteorites MIL 03346 and NWA 817. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.02.020]
Copyright Elsevier

^1,2David Morate, ^1,2Julia de León, ³Mário De Prá, ^1,2Javier Licandro, ^1,4Antonio Cabrera-Lavers, ⁵Humberto Campins, ⁶Noemí Pinilla-Alonso, ⁷Víctor Alí-Lagoa

¹Instituto de Astrofísica de Canarias (IAC), C/vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
²Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
³Observatório Nacional, Coordenação de Astronomia e Astrofísica, 20921-400 Rio de Janeiro, Brazil
⁴GTC Project Office, 38205 La Laguna, Tenerife, Spain
⁵Physics Department, University of Central Florida, PO Box 162385, Orlando, FL 32816-2385, USA
⁶Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, 37996 TN, USA
⁷Laboratoire Lagrange, OCA, Boulevard de l’Observatoire, BP 4229 06304 Nice Cedex 04, France

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Reference
Morate D, de León J, De Prá M, Licandro J, Cabrera-Lavers A, Campins H, Pinilla-Alonso N, Alí-Lagoa V (2016) Compositional study of asteroids in the Erigone collisional family using visible spectroscopy at the 10.4 m GTC. Astronomy & Astrophysics 586, A129
Link to Article [http://dx.doi.org/10.1051/0004-6361/201527453]

The most popular papers on Cosmochemistry Papers in February were:

1-Schwarz WH, Trieloff M, Bollinger K, Gantert N, Fernandes VA, Meyer H-P, Povenmire H, Jessberger EK, Guglielmino M, Koeberl (2016) Coeval ages of Australasian, Central American and Western Canadian tektites reveal multiple impacts 790 ka ago. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.12.037]

2-Ebert S, Bischoff A (2016) Genetic relationship between Na-rich chondrules and Ca,Al-rich inclusions? – Formation of Na-rich chondrules by melting of refractory and volatile precursors in the Solar Nebula. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.014]

3-Nguyen AN, Keller LP, Messenger S (2016) MINERALOGY OF PRESOLAR SILICATE AND OXIDE GRAINS OF DIVERSE STELLAR ORIGINS. The Astrophysical Journal 818, 51
Link to Article [http://dx.doi.org/10.3847/0004-637X/818/1/51]

4-Hutzler A et al. (2016) Description of a very dense meteorite collection area in western Atacama: Insight into the long-term composition of the meteorite flux to Earth. Meteoritics & Planetary Sciences (in Press)
Link to Article [DOI: 10.1111/maps.12607]

5-Kawasaki N,Itoh S,Sakamoto N, Yurimoto H (2016) Chronological study of oxygen isotope composition for the solar protoplanetary disk recorded in a fluffy Type A CAI from Vigarano. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.12.031]

^1,2M. Marsset, ²P. Vernazza, ^3,4M. Birlan, ⁵F. DeMeo, ⁵R. P. Binzel, ¹C. Dumas, ¹J. Milli, ^3,4M. Popescu4,3
¹European Southern Observatory (ESO), Alonso de Córdova 3107, 1900 Casilla Vitacura, Santiago, Chile
²Aix Marseille University, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
³IMCCE, Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris Cedex, France
⁴Astronomical Institute of the Romanian Academy, 5 Cuţitul de Argint, 040557 Bucharest, Romania
⁵Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA

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Reference
Marsset M, Vernazza P, Birlan M, DeMeo F, Binzel RP, Dumas C, Milli J, Popescu M (2016) Compositional characterisation of the Themis family. Astronomy & Astrophysics 586 A15
Link to Article [http://dx.doi.org/10.1051/0004-6361/201526962]

¹C. Tubiana, ^1,2C. Snodgrass, ³R. Michelsen, ³H. Haack, ¹H. Böhnhardt, ⁴A. Fitzsimmons, ⁵I. P. Williams
¹Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 33077 Göttingen, Germany
²Planetary and Space Sciences, Department of Physical Sciences, The Open University, Milton Keynes, MK7 6AA, UK
³Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, 1350 Copenhagen, Denmark
⁴Astrophysics Research Centre, Department of Physics and Astronomy, Queen’s University Belfast, Belfast BT7 1NN, UK
⁵School of Physics and Astronomy, Queen Mary, University of London, London E1 4NS, UK

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Reference
Tubiana C, Snodgrass C, Michelsen R, Haack H, Böhnhardt H, Fitzsimmons A, Williams IP (2016) 2P/Encke, the Taurid complex NEOs and the Maribo and Sutter’s Mill meteorites. Astronomy & Astrophysics 584, A97
Link to Article [http://dx.doi.org/10.1051/0004-6361/201425512]

¹M. Hilchenbach (>10)*
¹Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
*Find the extensive, full author and affiliation list on the publishers website

The COmetary Secondary Ion Mass Analyser instrument on board ESA’s Rosetta mission has collected dust particles in the coma of comet 67P/Churyumov–Gerasimenko. During the early-orbit phase of the Rosetta mission, particles and particle agglomerates have been imaged and analyzed in the inner coma at distances between 100 km and 10 km off the cometary nucleus and at more than 3 AU from the Sun. We identified 585 particles of more than 14 μm in size. The particles are collected at low impact speeds and constitute a sample of the dust particles in the inner coma impacting and fragmenting on the targets. The sizes of the particles range from 14 μm up to sub-millimeter sizes and the differential dust flux size distribution is fitted with a power law exponent of −3.1. After impact, the larger particles tend to stick together, spread out or consist of single or a group of clumps, and the flocculent morphology of the fragmented particles is revealed. The elemental composition of the dust particles is heterogeneous and the particles could contain typical silicates like olivine and pyroxenes, as well as iron sulfides. The sodium to iron elemental ratio is enriched with regard to abundances in CI carbonaceous chondrites by a factor from ~1.5 to ~15. No clear evidence for organic matter has been identified. The composition and morphology of the collected dust particles appear to be similar to that of interplanetary dust particles.

Reference
Hilchenbach M et al. (2016) COMET 67P/CHURYUMOV–GERASIMENKO: CLOSE-UP ON DUST PARTICLE FRAGMENTS. The Astrophysical Journal (Letters) 816, L32
Link to Article [http://dx.doi.org/10.3847/2041-8205/816/2/L32http://dx.doi.org/10.3847/2041-8205/816/2/L32]