¹G. W. Evatt, ¹M. J. Coughlan, ²K. H. Joy, ³A. R. D. Smedley, ³P. J. Connolly,
¹I. D. Abrahams
¹UK School of Mathematics, University of Manchester, Manchester M13 9PL, UK
²The School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK
³Centre for Atmospheric Science, The School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK

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Reference
Evatt GW, Coughlan MJ, Joy KH, Smedley ARD, Connolly PJ, Abrahams ID (2016) A potential hidden layer of meteorites below the ice surface of Antarctica. Nature Communications 7, Article number: 10679
Link to Article [doi:10.1038/ncomms10679]

¹Michael A. Velbel
¹Division of Meteorites, Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th and Constitution Avenues NW, Washington, DC 20560-0119

Several nakhlites (clinopyroxenite meteorites from Mars) contain olivine phenocrysts with corrosion features identical in size, shape and distribution to the smaller etch-pits of well-characterized weathered terrestrial olivine. Miller Range (MIL) 03346 is an Antarctic nakhlite find, recovered after long exposure to Antarctic conditions. The distribution of discrete olivine etch-pits almost exclusively within a few hundred microns of allocation MIL 03346,171’s documentably exposed surface suggests that they formed by terrestrial weathering in Antarctica. The small size of olivine etch-pits in MIL 03346,171 relative to commonly much larger etch-pits in even incipiently weathered terrestrial examples suggests that the duration of its exposure to weathering conditions was short, or the weathering conditions to which it was exposed did not favor olivine corrosion (in the form of etch-pit formation), or both. Time-scales for the formation of etch-pits, estimated from experimentally determined dissolution rates of olivine over a range of pHs, are comparable to the measured terrestrial age of the meteorite and short relative to the time available for possible similar corrosion on Mars. Etch-pits of the observed size on MIL 03346 olivine phenocrysts would be relatively easy to form supraglacially under brief episodic acidic Antarctic conditions, but the terrestrial age of MIL 03346 is long enough that its olivine might have been weathered to the observed state by englacial films of alkaline Antarctic water. The paucity of similar etch-pits in olivine from the interior of MIL 03346 suggests that olivine in this Mars meteorite was exposed to even less aqueous alteration after iddingsitization during its 1.3 billion years on Mars than its exterior was subjected to during its Pleistocene-Holocene exposure to Antarctic weathering conditions.

Reference
Velbel MA (2016) Aqueous Corrosion of Olivine in the Mars Meteorite Miller Range (MIL) 03346 During Antarctic Weathering: Implications for Water on Mars. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.01.036]
Copyright Elsevier

¹Agnese Fazio, ¹Massimo D’Orazio, ^2,3Carole Cordier, ¹Luigi Folco
¹Dipartimento di Scienze della Terra, Università di Pisa, Via S. Maria 53, I-56126 Pisa, Italy
²Université de Grenoble Alpes, ISTerre, BP 53, F-38041 Grenoble CEDEX 9, France
³CNRS, ISTerre, BP 53, F-38041 Grenoble CEDEX 9, France

In small meteorite impacts, the projectile may survive through fragmentation; in addition, it may melt, and chemically and physically interact with both shocked and melted target rocks. However, the mixing/mingling between projectile and target melts is a process still not completely understood. Kamil Crater (45 m in diameter; Egypt), generated by the hypervelocity impact of the Gebel Kamil Ni-rich ataxite on sandstone target, allows to study the target-projectile interaction in a simple and fresh geological setting. We conducted a petrographic and geochemical study of macroscopic impact melt lapilli and bombs ejected from the crater, which were collected during our geophysical campaign in February 2010. Two types of glasses constitute the impact melt lapilli and bombs: a white glass and a dark glass. The white glass is mostly made of SiO2 and it is devoid of inclusions. Its negligible Ni and Co contents suggest derivation from the target rocks without interaction with the projectile (<0.1 wt% of projectile contamination). The dark glass is a silicate melt with variable contents of Al2O3 (0.84-18.7 wt%), FeOT (1.83-61.5 wt%), and NiO (<0.01-10.2 wt%). The dark glass typically includes fragments (from few μm to several mm in size) of shocked sandstone, diaplectic glass, lechatelierite, and Ni-Fe metal blebs. The metal blebs are enriched in Ni compared to the Gebel Kamil meteorite. The dark glass is thus a mixture of target and projectile melts (11-12 wt% of projectile contamination). Based on recently proposed models for target-projectile interaction and for impact glass formation, we suggest a scenario for the glass formation at Kamil. During the transition from the contact and compression stage and the excavation stage, projectile and target liquids formed at their interface and chemically interact in a restricted zone. Projectile contamination affected only a shallow portion of the target rocks. The SiO2 melt that eventually solidified as white glass behaved as an immiscible liquid and did not interact with the projectile. During the excavation stage dark glass melt engulfed and coated the white glass melt, target fragments, and got stuck to iron meteorite shrapnel fragments. This model could also explain the common formation of white and dark glasses in small impact craters generated by iron bodies (e.g., Wabar).

Reference
Fazio A, D’Orazio M, Cordier C, Folco L (2016) Target-projectile interaction during impact melting at Kamil Crater, Egypt. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2016.02.003]
Copyright Elsevier

^1,2Ann N. Nguyen, ¹Lindsay P. Keller, ¹Scott Messenger
¹Robert M. Walker Laboratory for Space Science, EISD Directorate, Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
²JETS/Jacobs Technology, NASA JSC, Houston, TX 77058, USA

We report the chemical and structural analysis of nine presolar silicate grains and one presolar oxide grain from the ungrouped chondrite Acfer 094 and the CR chondrite Queen Alexandra Range 99177. Oxygen isotopic analyses indicate that five of these grains condensed in the outflows of asymptotic giant branch (AGB) stars, four have supernova (SN) origins, and one grain likely has a nova origin. Transmission electron microscopy studies show that most of the grains are amorphous with widely varying non-stoichiometric chemical compositions. Three crystalline AGB grains were identified: a clinoenstatite-containing grain assemblage, a Fe-rich olivine grain, and a nanocrystalline enstatite grain encased in an amorphous silicate shell. An amorphous stoichiometric enstatite (MgSiO3) SN grain likely condensed as a crystal and was later rendered amorphous. We do not observe a systematic difference in the chemistries and mineralogies of presolar silicates from different stellar sources, suggesting that the grains formed under a similar range of conditions.

Reference
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]

¹Hiroshi Hidaka, ¹Takuya Higuchi, ²Shigekazu Yoneda
¹Department of Earth and Planetary Systems Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
²Department of Science and Engineering, National Museum of Nature and Science, Tsukuba 305-0005, Japan

It is known that the Sayama meteorite (CM2) shows an extensive signature for aqueous alteration on the meteorite parent body, and that most of the primary minerals in the chondrules are replaced with phyllosilicates as the result of the aqueous alteration. In this paper, it is confirmed from the observation of two-dimensional Raman spectra that a part of olivine in a chondrule collected from the Sayama chondrite is serperntinized. Ion microprobe analysis of the chondrule showed that alkaline elements such as Rb and Cs are heterogeneously redistributed in the chondrule. The result of higher Rb and Cs contents in serpentinized phases in the chondrule rather than in other parts suggested the selective adsorption of alkaline elements into the serpentine in association with early aqueous activity on the meteorite parent body. Furthermore Ba isotopic analysis provided variations of 135Ba/138Ba and 137Ba/138Ba in the chondrule. This result was consistent with our previous isotopic data suggesting isotopic evidence for the existence of the presently extinct nuclide 135Cs in the Sayama meteorite, but the abundance of 135Cs in the solar system remains unclear because of large analytical uncertainties.

Reference
Hidaka H, Higuchi T, Yoneda S (2015) REDISTRIBUTION OF ALKALINE ELEMENTS IN ASSOCIATION WITH AQUEOUS ACTIVITY IN THE EARLY SOLAR SYSTEM. The Astrophysical Journal 815, 76
Link to Article [http://dx.doi.org/10.1088/0004-637X/815/1/76]

¹N. G. Rudraswami, ¹M. Shyam Prasad, ^1,2S. Dey, ³J. M. C. Plane, ³W. Feng, ⁴S. Taylor
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403004, India
²Indian Institute of Technology, Roorkee, Uttarakhand 247667, India
³School of Chemistry, University of Leeds, Leeds LS2 9JT, UK
⁴Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755-1290, USA

We evaluate the heating of extraterrestrial particles entering the atmosphere using the comprehensive chemical ablation model (CABMOD). This model predicts the ablation rates of individual elements in a particle with a defined size, composition, entry velocity, and entry angle with respect to the zenith (ZA). In the present study, bulk chemical analyses of 1133 Antarctica micrometeorites (collected from the south pole water well) are interpreted using CABMOD. The marked spread in Fe/Si values in unmelted, partially melted, and melted micrometeorites is explained by the loss of relatively volatile Fe during atmospheric entry. The combined theoretical modeling and elemental composition of the micrometeorites (Mg/Si ratios) suggest that ~85% of particles have a provenance of carbonaceous chondrites, the remaining ~15% are either ordinary or enstatite chondrites. About 65% of the micrometeorites have undergone <20% ablation, while a further 20% have lost between 20% and 60% of their original mass. This has implications for understanding the micrometeorite flux that reaches the Earth’s surface, as well as estimating the pre-atmospheric size of the particles. Our work shows that the unmelted particles that contribute ~50% to the total micrometeorite collection on Earth’s surface have a small entry zone: ZA = 60°–90° if the entry velocity is ~11 km s−1, and ZA = 80°–90° for >11–21 km s−1.

Reference
Rudraswami NG, Shyam Prasad M, Dey S, Plane JMC, Feng W, Taylor S (2015) EVALUATING CHANGES IN THE ELEMENTAL COMPOSITION OF MICROMETEORITES DURING ENTRY INTO THE EARTH’S ATMOSPHERE. The Astrophysicla Journal 814, 78
Link to Article [http://dx.doi.org/10.1088/0004-637X/814/1/78]

¹M. Lemelin, ¹P.G. Lucey, ²G.A. Neumann, ²E.M. Mazarico, ³M.K. Barker, ¹A. Kakazu, ¹D. Trang, ⁴D.E. Smith, ⁴M.T. Zuber
¹Hawaii Institute of Geophysics and Planetology, Dept. of Geophysics and Geology, University of Hawaii at Manoa, 1680 East-West Rd, Honolulu HI
²Goddard Space Flight Center, 8800 Greenbelt Rd., Greenbelt, MD 20771
³Sigma Space Corporation, 4600 Forbes Blvd., Lanham MD 20706
⁴Dept. of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Ave. Cambridge, MA 02139

The Lunar Orbiter Laser Altimeter (LOLA) experiment on Lunar Reconnaissance Orbiter (LRO) is a laser altimeter that also measures the strength of the return pulse from the lunar surface. These data have been used to estimate the reflectance of the lunar surface, including regions lacking direct solar illumination. A new calibration of these data are presented that features lower uncertainties overall and more consistent results in the polar regions. We use these data, along with newly available maps of the distribution of lunar maria, also derived from LRO instrument data, to investigate a newly discovered dependence of the albedo of the lunar maria on latitude (Hemingway et al. 2015). We confirm that there is an increase in albedo with latitude in the lunar maria, and confirm that this variation is not an artifact arising from the distribution of compositions within the lunar maria, using data from the Lunar Prospector neutron spectrometer. Radiative transfer modeling of the albedo dependence within the lunar maria is consistent with the very weak to absent dependence of albedo on latitude in the lunar highlands; the lower abundance of the iron source for space weathering products in the lunar highlands weakens the latitude dependence to the extent that it is only weakly detectable in current data. In addition, photometric models and normalization may take into account the fact that the lunar albedo is latitude dependent, but this dependence can cause errors in normalized reflectance of at most 2 % for the majority of near-nadir geometries. We also investigate whether the latitude dependent albedo may have obscured detection of small mare deposits at high latitudes. We find that small regions at high latitudes with low roughness similar to the lunar maria are not mare deposits that may have been misclassified owing to high albedos imposed by the latitude dependence. Finally, we suggest that the only modest correlations among space weathering indicators defined for the lunar samples may be due to mixing of soils from distinct latitudes.

Reference
Lemelin M, Lucey PG, Neumann GA, Mazarico EM, Barker MK, Kakazu A, Trang D, Smith DE, Zuber MT (2016) Improved calibration of reflectance data from the LRO Lunar Orbiter Laser Altimeter (LOLA) and implications for space weathering. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.02.006]
Coypright Elsevier

¹F.Zambon et al. (>10)*
¹INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, 00133 Rome, Italy
*Find the extensive, full author and affiliation list on the publishers website

Vesta’s surface is mostly composed of pyroxene-rich lithologies compatible with howardite, eucrite and diogenite (HED) meteorites (e.g., Feierberg, Drake, 1980 and McCord, Adams, Johnson, 1970). Data provided by the Visible and Infrared (VIR) spectrometer, onboard the NASA Dawn spacecraft, revealed that all Vesta reflectance spectra show absorption bands at ∼ 0.9 μm and ∼ 1.9 μm, which are typical of iron-bearing pyroxenes ( De Sanctis et al., 2012a). Other minerals may be present in spectrally significant concentrations; these include olivine and opaque phases like those found in carbonaceous chondrites. These additional components modify the dominant pyroxene absorptions. We apply linear spectral unmixing on bright material (BM) units of Vesta to identify HEDs and non-HED phases. We explore the limits of applicability of linear spectral unmixing, testing it on laboratory mixtures. We find that the linear method is applicable at the VIR pixel resolution and it is useful when the surface is composed of pyroxene-rich lithologies containing moderate quantities of carbonaceous chondrite, olivine, and plagioclase. We found three main groups of BM units: eucrite-rich, diogenite-rich, and olivine-rich. For the non-HED spectral endmember, we choose either olivine or a featureless component. Our work confirms that Vesta’s surface contains a high content of pyroxenes mixed with a lower concentration of other phases. In many cases, the non-HED endmember that gives the best fit is the featureless phase, which causes a reduction in the strength of both bands. The anticorrelation between albedo and featureless endmember indicates that this phase is associated with low-albedo, CC-like opaque material. Large amounts of olivine have been detected in Bellicia, Arruntia and BU14 BM units. Other sites present low olivine content ( < 30%) mostly with a high concentration of diogenite.

Reference
Zambon F et al. (2016) Lithologic variation within bright material on Vesta revealed by linear spectral unmixing. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2016.01.009]
Copyright Elsevier

^1,3Anna Neubeck, ²Marek Tulej, ³Magnus Ivarsson, ¹Curt Bromana, ²Andreas Riedo, ⁴Sean McMahon, ²Peter Wurz, ³Stefan Bengtson
¹Department of Geological Sciences, Stockholm University, Svante Arrhenius väg 8, 106 91 Stockholm, Sweden
²Space Research and Planetary Sciences, Physics Institute, University of Bern, CH-3012 Bern, Switzerland
³Department of Palaeobiology and Nordic Center for Earth Evolution (NordCEE), Swedish Museum of Natural History, Stockholm, Sweden
⁴Department of Geology & Geophysics, Yale University, Connecticut, USA

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Reference
Neubeck A, Tulej M, Ivarsson M, Broman C, Riedo A, McMahon S, Wurz P, Bengtson S (2015) Mineralogical determination in situ of a highly heterogeneous material using a miniaturized laser ablation mass spectrometer with high spatial resolution. International Journal of Astrobiology (in Press)
Link to Article [DOI: http://dx.doi.org/10.1017/S1473550415000269]

¹Alian Wang,¹Bradley L. Jolliff,²Yang Liu,¹Kathryn Connor
¹Dept. Earth and Planetary Sciences and McDonnell Center for Space Sciences, Washington University in St. Louis, USA
²Southwest Research Institute, San Antonio, Texas, USA

Monohydrated Mg sulfate (MgSO4·H2O) and polyhydrated sulfate are the most common and abundant hydrous sulfates observed thus far on Mars. They are widely distributed and coexist in many locations. On the basis of results from two new sets of experiments, in combination with past experimental studies and the subsurface salt mineralogy observed at a saline playa (Dalangtan, DLT) in a terrestrial analogue hyperarid region on the Tibet Plateau, we can now set new constraints on the nature and origin of these two major martian sulfates. Starkeyite (MgSO4·4H2O) is the best candidate for polyhydrated sulfate. MgSO4·H2O in the form of “LH-1w” [Wang et al., 2009], generated from dehydration of Mg-sulfates with high degrees of hydration, is the most likely mineral form for the majority of martian monohydrated Mg-sulfate. Two critical properties of Mg-sulfates are responsible for the coexistence of these two phases that have very different degrees of hydration: (1) the metastability of a sub-structural unit in starkeyite at relatively low temperatures; and (2) catalytic effects attributed to co-precipitated species (sulfates, chlorides, oxides, and hydroxides) from chemically complex brines that help overcome the metastability of starkeyite. The combination of these two properties controls the coexistence of the LH-1w layer and starkeyite layers at many locations on Mars, which sometimes occur in an interbedded stratigraphy. The structural H2O held by these two broadly distributed sulfates represents a large H2O reservoir at the surface and in the shallow subsurface on current Mars.

Reference
Wang A, Jolliff BL, Liu Y, Connor K (2016) Setting Constraints on the Nature and Origin of the two Major Hydrous Sulfates on Mars — Monohydrated and Polyhydrated Sulfates. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004889]
Published by arrangement with John Wiley&Sons