¹Dell’Aglio, M., ^1,2De Giacomo, A., ¹Gaudiuso, R., ¹De Pascale, O., ^2,3Longo, S.
¹CNR-IMIP, Via Amendola 122/D, 70126 Bari, Italy
²Chemistry Department, University of Bari, Via Orabona 4, 70126 Bari, Italy
³INAF-Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, Firenze, Italy

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Reference
Dell’Aglio M, De Giamoco A, Gaudiuso R, De Pascale O, Longo S (2014) Laser Induced Breakdown Spectroscopy of meteorites as a probe of the early solar System. Spectrochimica Acta – Part B Atomic Spectroscopy 101,68-75
Link to Article [DOI: 10.1016/j.sab.2014.07.011]

^1,2Burton, A.S., ^2,3Grunsfeld, S., ²Elsila, J.E., ²Glavin, D.P., ²Dworkin, J.P.
¹NASA Johnson Space Center, KR, 2101 NASA Parkway, Houston, TX 77058, United States
²NASA Goddard Space Flight Center, Solar System Exploration Division, 8800 Greenbelt Road, Maryland 20771, United States
³River Hill High School, 12101 Clarksville Pike, Clarksville, MD 21029, United States

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Reference
Burton AS, Grunsfeld S, Elsila JE, Glavin DP, Dworkin JP (2014) The effects of parent-body hydrothermal heating on amino acid abundances in CI-like chondrites. Polar Science 8, 3 255-263
Link to Article [DOI: 10.1016/j.polar.2014.05.002]

¹George J. Flynn et al. (>10)*
¹SUNY Plattsburgh, Plattsburgh, New York, USA
*Find the extensive, full author and affiliation list on the publishers Website

The NASA Stardust spacecraft exposed an aerogel collector to the interstellar dust passing through the solar system. We performed X-ray fluorescence element mapping and abundance measurements, for elements 19 ≤ Z ≤ 30, on six “interstellar candidates,” potential interstellar impacts identified by Stardust@Home and extracted for analyses in picokeystones. One, I1044,3,33, showed no element hot-spots within the designated search area. However, we identified a nearby surface feature, consistent with the impact of a weak, high-speed particle having an approximately chondritic (CI) element abundance pattern, except for factor-of-ten enrichments in K and Zn and an S depletion. This hot-spot, containing approximately 10 fg of Fe, corresponds to an approximately 350 nm chondritic particle, small enough to be missed by Stardust@Home, indicating that other techniques may be necessary to identify all interstellar candidates. Only one interstellar candidate, I1004,1,2, showed a track. The terminal particle has large enrichments in S, Ti, Cr, Mn, Ni, Cu, and Zn relative to Fe-normalized CI values. It has high Al/Fe, but does not match the Ni/Fe range measured for samples of Al-deck material from the Stardust sample return capsule, which was within the field-of-view of the interstellar collector. A third interstellar candidate, I1075,1,25, showed an Al-rich surface feature that has a composition generally consistent with the Al-deck material, suggesting that it is a secondary particle. The other three interstellar candidates, I1001,1,16, I1001,2,17, and I1044,2,32, showed no impact features or tracks, but allowed assessment of submicron contamination in this aerogel, including Fe hot-spots having CI-like Ni/Fe ratios, complicating the search for CI-like interstellar/interplanetary dust.

Reference
Flynn GJ et al. (2014) Stardust Interstellar Preliminary Examination VII: Synchrotron X-ray fluorescence analysis of six Stardust interstellar candidates measured with the Advanced Photon Source 2-ID-D microprobe. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12144]

Published by arrangement with John Wiley & Sons

^1,2F. Postberg et al. (>10)*
¹Institut für Raumfahrtsysteme, Universität Stuttgart, Germany
²Institut für Geowissenschaften, Universität Heidelberg, Germany
*Find the extensive, full author and affiliation list on the publishers website

The NASA Stardust mission used silica aerogel slabs to slowly decelerate and capture impinging cosmic dust particles for return to Earth. During this process, impact tracks are generated along the trajectory of the particle into the aerogel. It is believed that the morphology and dimensions of these tracks, together with the state of captured grains at track termini, may be linked to the size, velocity, and density of the impacting cosmic dust grain. Here, we present the results of laboratory hypervelocity impact experiments, during which cosmic dust analog particles (diameters of between 0.2 and 0.4 μm), composed of olivine, orthopyroxene, or an organic polymer, were accelerated onto Stardust flight-spare low-density (approximately 0.01 g cm−3) silica aerogel. The impact velocities (3–21 km s−1) were chosen to simulate the range of velocities expected during Stardust’s interstellar dust (ISD) collection phases. Track lengths and widths, together with the success of particle capture, are analyzed as functions of impact velocity and particle composition, density, and size. Captured terminal particles from low-density organic projectiles become undetectable at lower velocities than those from similarly sized, denser mineral particles, which are still detectable (although substantially altered by the impact process) at 15 km s−1. The survival of these terminal particles, together with the track dimensions obtained during low impact speed capture of small grains in the laboratory, indicates that two of the three best Stardust candidate extraterrestrial grains were actually captured at speeds much lower than predicted. Track length and diameters are, in general, more sensitive to impact velocities than previously expected, which makes tracks of particles with diameters of 0.4 μm and below hard to identify at low capture speeds (<10 km s−1). Therefore, although captured intact, the majority of the interstellar dust grains returned to Earth by Stardust remain to be found.

Reference
Postberg F et al. (2014) Stardust Interstellar Preliminary Examination IX: High-speed interstellar dust analog capture in Stardust flight-spare aerogel. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12173]

Published by arrangement with John Wiley & Sons

^1,2,3K.H. Joy, ^4,5A. Nemchin, ⁴M. Grange, ^3,6T.J. Lapen, ^7,8A.H. Peslier,^7,8D.K. Ross, ^2,8M.E. Zolensky, ^1,2D.A. Kring
¹The Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, Texas, 77058, TX, 77204-5007, USA
²NASA Lunar Science Institute
³Permanent address: School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester, M13 9PL, UK
⁴Curtin University of Technology, Perth, WA 6845, Australia
⁵Swedish Museum of Natural History, S-104 05 Stockholm, Sweden
⁶University of Houston, Department of Earth and Atmospheric Sciences, TX, USA
⁷Jacobs Technology, JETS, Mail Code JE23, 2224 Bay Area Blvd, Houston, TX 77058, USA
⁸Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA

Dhofar (Dho) 925, 961 and Sayh al Uhaymir (SaU) 449 are brecciated lunar meteorites consisting of mineral fragments and clasts from a range of precursor lithologies including magnesian anorthositic gabbronorite granulites; crystalline impact melt breccias; clast-bearing glassy impact melt breccias; lithic (fragmental) breccias; mare basalts; and evolved (silica-rich) rocks. On the similarity of clast type and mineral chemistry the samples are likely grouped, and were part of the same parent meteorite. Phosphate Pb-Pb ages in impact melt breccias and matrix grains demonstrate that Dho 961 records geological events spanning ∼500 Ma between 4.35 Ga to 3.89 Ga. These Pb-Pb ages are similar to the ages of ‘ancient’ intrusive magmatic samples and impact basin melt products collected on the lunar nearside by the Apollo missions. However, the samples’ bulk rock composition is chemically distinct from these types of samples, and it has been suggested that they may have originated from the farside South Pole-Aitken impact basin (i.e., Jolliff et al., 2008). We test this hypothesis, and conclude that although it is possible that the samples may be from the South Pole-Aitken basin, there are other regions on the Moon that may have also sourced these complex breccias.

References
Joy KH, Nemchin A, Grange M, Lapen TJ, Peslier AH, Ross DK, Zolensky ME, Kring DA (2014) Petrography, geochronology and source terrain characteristics of lunar meteorites Dhofar 925, 961 and Sayh al Uhaymir 449. Geochimica et Cosmochimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.08.013]

Copyright Elsevier

^1,2Clive R. Neal, ^1,2Patrick Donohue, ^1,2,3Amy L. Fagan,^1,2Katie O’Sullivan, ¹Jocelyn Oshrin, ^1,2Sarah Roberts
¹Department of Civil & Env. Eng. & Earth Sciences, University of Notre Dame, Notre Dame, IN 46556, USA1
²NASA Lunar Science Institute
³Center for Lunar Science and Exploration, Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX, 77058, USA

Impact processes play an important role in shaping and reshaping the surfaces of airless planetary bodies. Such processes produce regoliths and generate melts that crystallize and record the homogenization of the geology at the impact site. If the volume of melt is substantial, the resultant crystallized product has an igneous texture and may be free of xenolithic clasts making it difficult to distinguish from melts produced by endogenic magmatic processes. This has been clearly demonstrated during the return of the Apollo samples from the Moon, where Apollo 14 basalt 14310 was initially described as a mare basalt and was only subsequently reclassified as an impact melt following detailed and time consuming crystallization experiments. Another way of distinguishing lunar impact melts from endogenically-derived mare basalts is through the quantification of the highly siderophile elements (Pd, Rh, Ru, Ir, Pt, Os), which have relatively low abundances in pristine lunar samples but are high in meteorites and, therefore, may be enriched in impact melts. However, these analyses consume relatively large quantities of valuable sample and because of mass constraints cannot be performed on many lunar samples. In this paper we present a quantitative petrographic method that has the potential to distinguish lunar impact melts from endogenically-derived mare basalts using plagioclase and olivine crystal size distributions (CSDs). The slopes and intercepts of these CSDs are used to show that olivine from impact melts displays a steeper CSD relative to olivine from mare basalts. For plagioclase, generally impacts melts display CSDs with shallower gradients than those from mare basalts and, as for olivines, plot in a distinct field on a CSD slope vs. CSD intercept plot. Using just a thin section to distinguish impact melts from mare basalts enables the goals of future robotic sample return missions to determine the age of the South Pole-Aitken basin in the Moon, because such missions will potentially only return small (2 to 4 mm) “rocklets” for analysis.

Reference
Neal CR, Donohue P, Fagan AL, O’Sullivan K, Oshrin J, Roberts S (2014) Distinguishing between basalts produced by endogenic volcanism and impact processes: A non-destructive method using quantitative petrography of lunar basaltic samples. Geochimica et Cosmochimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.08.020]

Copyright Elsevier

¹Matthew A. Pasek
¹School of Geosciences, University of South Florida, NES 207, 4202 E. Fowler Ave, Tampa FL 33620

Phosphorus is an important minor element on the Moon. It is moderately volatile and is found as both phosphates and phosphides in lunar material. The phosphides, such as schreibersite, are common to impact breccias at all Apollo sites. The origin of this schreibersite has been proposed to be a meteoritic contaminant, or alternatively produced in situ by reduction on the lunar surface. I propose that schreibersite and other siderophilic P phases have an origin from impact volatilization of phosphates at the lunar oxygen fugacity, followed by reaction of P gases with metal to form metal phosphides. This pathway is broadly consistent with the composition and structure of metal grains, as well as the native oxygen fugacity of the lunar surface. Additionally, this pathway suggests schreibersite is widespread across the lunar surface and likely on other planetary bodies, and hence may serve as a good P source for in situ resource utilization.

Reference
Pasek MA (2014) Phosphorus as a lunar volatile. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.07.031]

Copyright Elsevier