¹F. Tosi et al. (>10)*
¹INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, I-00133 Rome, Italy
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Quadrangle Av-10 ‘Oppia’ is one of five quadrangles that cover the equatorial region of asteroid (4) Vesta. This quadrangle is notable for the broad, spectrally distinct ejecta that extend south of the Oppia crater. These ejecta exhibit the steepest (‘reddest’) visible spectral slope observed across the asteroid and have distinct color properties as seen in multispectral composite images. Compared to previous works that focused on the composition and nature of unusual (‘orange’) ejecta found on Vesta, here we take into account a broader area that includes several features of interest, with an emphasis on mineralogy as inferred from data obtained by Dawn’s Visible InfraRed mapping spectrometer (VIR). Our analysis shows that the older northern and northeastern part of Av-10 is dominated by howardite-like material, while the younger southwestern part, including Oppia and its ejecta blanket, has a markedly eucritic mineralogy. The association of the mineralogical information with the geologic and topographic contexts allows for the establishment of relationships between the age of the main formations observed in this quadrangle and their composition. A major point of interest in the Oppia quadrangle is the spectral signature of hydrous material seen at the local scale. This material can be mapped by using high-resolution VIR data, combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Hydrated mineral phases studied previously on Vesta generally correlate with low-albedo material delivered by carbonaceous asteroids. However, our analysis shows that the strongest OH signature in Av-10 is found in a unit west of Oppia, previously mapped as ‘light mantle material’ and showing moderate reflectance and a red visible slope. With the available data we cannot yet assess the presence of water in this material. However, we offer a possible explanation for its origin.

Reference
Tosi F et al. (2015) Mineralogical analysis of the Oppia quadrangle of asteroid (4) Vesta: Evidence for occurrence of moderate-reflectance hydrated Minerals. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.018]

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¹M.C. De Sanctis et al. (>10*)
¹INAF, Istituto di Astrofisica e Planetologia Spaziali, Area di Ricerca di Tor Vergata, 00133 Roma, Italy
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The equatorial Marcia quadrangle region is characterized by the large, relatively young impact craters Marcia and Calpurnia and their surrounding dark ejecta field, a hill with a dark-rayed crater named Aricia Tholus, and an unusual diffuse material surrounding the impact crater Octavia. The spectral analysis indicates that while this region is relatively uniform in the pyroxene band centers, it instead shows large differences in pyroxene band depths and reflectance. A large variation of reflectance is seen in the quadrangle: bright and dark materials are present as diffuse material, and as concentrated spots and outcrops. Moreover, OH signature is pervasive in the quadrangle, with a few exceptions. The region, especially the Marcia ejecta field, is characterized by spectra showing the 2 μm band shifted at long wavelenghts. This is commonly associated with eucritic material, believed to have crystallized as lava on Vesta’s surface or within relatively shallow-level dikes and plutons, thus suggesting that this region is a remnant of the old Vestan basaltic crust. However, other characteristics of the spectra do not fully fit the eucritic composition, indicating an alternative explanation for the band center distribution, including the presence of carbonaceous chondritic material mixed with the native Vestan pyroxene.
The detailed mineralogical analysis of the Marcia quadrangle indicates that this quadrangle is the result of the mixture of the Vestan “endogenic” minerals with the “exogenic” carbonaceous chondrites. The stratigraphic units around Marcia clearly show the bright, uncontaminated material interlaced and mixed with the dark material that contains a strong OH signature. Only few small areas can be considered as representative of the old Vestan original material.

Reference
De Sanctis MC et al. (2015) Eucritic crust remnants and the effect of in-falling hydrous carbonaceous chondrites characterizing the composition of Vesta’s Marcia Region. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.014]

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¹Hanley, J., ²V. F. Chevrier, ³R. S. Barrows, ²C. Swaffer, ²T. S. Altheide
¹Department of Space Studies, Southwest Research Institute, Boulder, Colorado, USA
²Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, Arkansas, USA
³Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, Colorado, USA

The presence and distribution of oxychlorine salts (e.g. chlorates and perchlorates) on Mars has implications for the stability of water, most notably that they lower the freezing temperature. To date, elemental chlorine has been measured by all lander missions, with the perchlorate ion identified at both the Phoenix and Curiosity landing sites, but detection by near-infrared (NIR) and mid-infrared (MIR) remote sensing has been limited to deposits of anhydrous chlorides. Given that oxychlorine salts can form numerous hydrated phases, we have measured their NIR and MIR reflectance spectra from 1–25 µm for comparison to data collected from orbiting spectrometers. Anhydrous oxychlorine salts show almost no features in the NIR, except for small bands of residual adsorbed water. However, hydrated oxychlorine salts show numerous features due to water in the NIR, specifically at ~1.4 and ~1.9 µm. Increasing the hydration state increases the depth and width of the water bands. All oxychlorine salts exhibit an additional feature at ~2.2 µm due to a Cl-O combination or overtone feature, though it is less prominent in the hydrated perchlorate salts, likely overwhelmed by the ClO4-H2O feature at 2.14 µm. All oxychlorine salts show features in the MIR, due to the fundamental vibrations of Cl-O longward of ~8 µm. The NIR spectral features of hydrated oxychlorine salts are similar to other hydrated salts, especially hydrated sulfates, thus identification from orbit may be ambiguous; however, by utilizing the NIR and MIR laboratory data presented here for comparison, oxychlorine salts may be detectable by orbiting spectrometers.

Reference
Hanley J, Chevrier VF, Barrows RS, Swaffer C, Altheide TS (2015) Near- and mid-infrared reflectance spectra of hydrated oxychlorine salts with implications for Mars. Journal of Geophysical Research Planets, 120
Link to Article [doi:10.1002/2013JE004575]

Published by arrangement with John Wiley&Sons

¹F. Hörz,²P. D. Archer Jr., ³P. B. Niles, ⁴M. E. Zolensky, ^3,4M. Evans
¹LZ Technology Inc., Houston, Texas, USA
²Jacobs, NASA Johnson Space Center, Houston, Texas, USA
³ARES, NASA Johnson Space Center, Houston, Texas, USA
⁴Texas A&M University, College Station, Texas, USA

We have investigated the carbonates in the impact melts and in a monolithic clast of highly shocked Coconino sandstone of Meteor Crater, AZ to evaluate whether melting or devolatilization is the dominant response of carbonates during high-speed meteorite impact. Both melt- and clast-carbonates are calcites that have identical crystal habits and that contain anomalously high SiO2 and Al2O3. Also, both calcite occurrences lack any meteoritic contamination, such as Fe or Ni, which is otherwise abundantly observed in all other impact melts and their crystallization products at Meteor Crater. The carbon and oxygen isotope systematics for both calcite deposits suggest a low temperature environment (100 °C) for their precipitation from an aqueous solution, consistent with caliche. We furthermore subjected bulk melt beads to thermogravimetric analysis and monitored the evolving volatiles with a quadrupole mass spectrometer. CO₂ yields were <5 wt%, with typical values in the 2 wt% range; also total CO₂ loss is positively correlated with H₂O loss, an indication that most of these volatiles derive from the secondary calcite. Also, transparent glasses, considered the most pristine impact melts, yield 100 wt% element totals by EMPA, suggesting complete loss of CO₂. The target dolomite decomposed into MgO, CaO, and CO₂; the CO₂ escaped and the CaO and MgO combined with SiO₂ from coexisting quartz and FeO from the impactor to produce the dominant impact melt at Meteor Crater. Although confined to Meteor Crater, these findings are in stark contrast to Osinski et al. (2008) who proposed that melting of carbonates, rather than devolatilization, is the dominant process during hypervelocity impact into carbonate-bearing targets, including Meteor Crater.

Reference
Hörz F, Archer Jr. PD, Niles PB, Zolensky ME, Evans M (2015) Devolatilization or melting of carbonates at Meteor Crater, AZ? Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12453]

Published by arrangement with John Wiley&Sons

¹M. Shyam Prasad, ¹N. G. Rudraswami, ¹Agnelo De Araujo, ²E. V. S. S. K. Babu, ²T. Vijaya Kumar
¹CSIR—National Institute of Oceanography, Dona Paula, Goa, India
²LAM-ICP-MS National Facility, CSIR-National Geophysical Research Institute, Hyderabad, India

Extraterrestrial particulate materials on the Earth can originate in the form of collisional debris from the asteroid belt, cometary material, or as meteoroid ablation spherules. Signatures that link them to their parent bodies become obliterated if the frictional heating is severe during atmospheric entry. We investigated 481 micrometeorites isolated from ~300 kg of deep sea sediment, out of which 15 spherules appear to have retained signatures of their provenance, based on their textures, bulk chemical compositions, and relict grain compositions. Seven of these 15 spherules contain chromite grains whose compositions help in distinguishing subgroups within the ordinary chondrite sources. There are seven other spherules which comprise either entirely of dusty olivines or contain dusty olivines as relict grains. Two of these spherules appear to be chondrules from an unequilibrated ordinary chondrite. In addition, a porphyritic olivine pyroxene (POP) chondrule-like spherule is also recovered. The bulk chemical composition of all the spherules, in combination with trace elements, the chromite composition, and presence of dusty olivines suggest an ordinary chondritic source. These micrometeorites have undergone minimal frictional heating during their passage through the atmosphere and have retained these features. These micrometeorites therefore also imply there is a significant contribution from ordinary chondritic sources to the micrometeorite flux on the Earth.

Reference
Shyam Prasad M, Rudraswami NG, De Araujo A, Babu EVSSK, Vijaya Kumar T (2015) Ordinary chondritic micrometeorites from the Indian Ocean. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12451]
Published by arrangement with John Wiley&Sons

¹Peter Hoppe, ²Katharina Lodders, ¹Wataru Fujiya
¹Max Planck Institute for Chemistry, Mainz, Germany
²Department of Earth & Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri, 63130, USA

We studied 14 presolar SiC mainstream grains for C-, Si-, and S-isotopic compositions and S elemental abundances. Ten grains have low levels of S contamination and CI chondrite-normalized S/Si ratios between 2 × 10−5 and 2 × 10−4. All grains have S-isotopic compositions compatible within 2σ of solar values. Their mean S isotope composition deviates from solar by at most a few percent, and is consistent with values observed for the carbon star IRC+10216, believed to be a representative source star of the grains, and the interstellar medium. The isotopic data are also consistent with stellar model predictions of low-mass asymptotic giant branch (AGB) stars. In a δ33S versus δ34S plot the data fit along a line with a slope of 1.8 ± 0.7, suggesting imprints from galactic chemical evolution. The observed S abundances are lower than expected from equilibrium condensation of CaS in solid solution with SiC under pressure and temperature conditions inferred from the abundances of more refractory elements in SiC. Calcium to S abundance ratios are generally above unity, contrary to expectations for stoichiometric CaS solution in the grains, possibly due to condensation of CaC2 into SiC. We observed a correlation between Mg and S abundances suggesting solid solution of MgS in SiC. The low abundances of S in mainstream grains support the view that the significantly higher abundances of excess 32S found in some Type AB SiC grains are the result of in situ decay of radioactive 32Si from born-again AGB stars that condensed into AB grains.

Reference
Hoppe P, Lodders K, Fujiya W (2015) Sulfur in presolar silicon carbide grains from asymptotic giant branch stars. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12449]

Published by arrangement with John Wiley&Sons

¹Steven B. Simon, ^1,2Lawrence Grossman
¹Department of the Geophysical Sciences, The University of Chicago, Chicago, Illinois, USA
²The Enrico Fermi Institute, The University of Chicago, Chicago, Illinois, USA

The Antarctic carbonaceous chondrites DOM 08004 and DOM 08006 have been paired and classified as CO3.0s. There is some uncertainty as to whether they should be paired and whether they are best classified as CO chondrites, but they provide an opportunity for the study of refractory inclusions that have not been modified by parent body processes. In this work, refractory inclusions in thin sections of DOM 08004 and 08006 are studied and compared with inclusions in ALHA77307 (CO3.0) and Acfer 094 (C3.0, ungrouped). Results show that the DOM samples have refractory inclusion populations that are similar to each other but not typical of CO3 chondrites; main differences are that the DOM samples are slightly richer in inclusions in general and, more specifically, in the proportions of grossite-bearing inclusions. In DOM 08004 and DOM 08006, 12.4% and 6.6%, respectively, of the inclusions are grossite-bearing. This is higher than the proportion found in Acfer 094 (5.2%), whereas none were found in ALHA77307. Like those in Acfer 094, DOM inclusions are small (mostly

Reference
Simon SB, Grossman L (2015) Refractory inclusions in the pristine carbonaceous chondrites DOM 08004 and DOM 08006. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12452]

Published by arrangement with John Wiley&Sons

¹A. A. Shiryaev,²A. V. Fisenko,³L. F. Semjonova,⁴A. A. Khomich,⁵I. I. Vlasov
¹Institute of Physical Chemistry and Electrochemistry RAS, Moscow, Russia
²Institute of Ore Deposits, Petrography, Geochemistry and Mineralogy RAS, Moscow, Russia
³Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Moscow, Russia
⁴General Physics Institute RAS, Moscow, Russia
⁵National Research Nuclear University MEPhI, Moscow, Russia

Photoluminescence spectra show that silicon impurity is present in lattice of some nanodiamond grains (ND) of various chondrites as a silicon-vacancy (SiV) defect. The relative intensity of the SiV band in the diamond-rich separates depends on chemical composition of meteorites and on size of ND grains. The strongest signal is found for the size separates enriched in small grains; thus, confirming our earlier conclusion that the SiV defects preferentially reside in the smallest (≤2 nm) grains. The difference in relative intensities of the SiV luminescence in the diamond-rich separates of individual meteorites are due to variable conditions of thermal metamorphism of their parent bodies and/or uneven sampling of nanodiamond populations. Annealing of separates in air eliminates surface sp2-carbon; consequently, the SiV luminescence is enhanced. Strong and well-defined luminescence and absorption of the SiV defect is a promising feature to locate cold (<250 °C) nanodiamonds in space.

Reference
Shiryaev AA, Fisenko AV, Semjonova LF, Khomich AA, Vlasov II (2015) Photoluminescence of silicon-vacancy defects in nanodiamonds of different chondrites. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12450]

Published by arrangement with John Wiley&Sons

^1,2Alan E. Rubin
¹Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA
²Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1567, USA

Maskelynite is a diaplectic glass that forms from plagioclase at shock pressures of ∼20-30 GPa, depending on the Ca concentration. The proportion of maskelynite-rich samples in a basaltic meteorite group correlates with the parent-body escape velocity and serves as a shock indicator of launching conditions. For eucrites (basalts widely presumed to be from Vesta; vesc = 0.36 km s-1), ∼5% of the samples are maskelynite rich. For the Moon (vesc = 2.38 km s-1), ∼30% of basaltic meteorites are maskelynite rich. For Mars (vesc = 5.03 km s-1), ∼93% of basaltic meteorites are maskelynite rich. In contrast, literature data show that maskelynite is rare (∼1%) among mare basalts and basaltic fragments in Apollo 11, 12, 15 and 17 soils (which were never ejected from the Moon). Angrites are unbrecciated basaltic meteorites that are maskelynite free; they were ejected at low-to-moderate shock pressures from an asteroid smaller than Vesta.

Because most impacts that eject materials from a large (⩾100 km) parent body are barely energetic enough to do that, a collision that has little more than the threshold energy required to eject a sample from Vesta will not be able to eject identical samples from the Moon or Mars. There must have been relatively few impacts, if any, that launched eucrites off their parent body that also imparted shock pressures of ∼20-30 GPa in the ejected rocks. More-energetic impacts were required to launch basalts off the Moon and Mars. On average, Vesta ejecta were subjected to lower shock pressures than lunar ejecta, and lunar ejecta were subjected to lower shock pressures than martian ejecta.

H and LL ordinary chondrites have low percentages of shock-stage S5 maskelynite-bearing samples (∼1% and ∼4%, respectively), probably reflecting shock processes experienced by these rocks on their parent asteroids. In contrast, L chondrites have a relatively high proportion of samples containing maskelynite (∼11%), most likely a result of catastrophic parent-body disruption 470 Ma ago.

Reference
Rubin AE (2015) Maskelynite in asteroidal, lunar and planetary basaltic meteorites: An indicator of shock pressure during impact ejection from their parent bodies. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.05.010]
Copyright Elsevier

¹Kazushige Tomeoka,²Ichiro Ohnishi
¹Department of Earth and Planetary Sciences, Faculty of Science, Kobe University, Nada, Kobe 657-8501, Japan
²EM Business Unit, JEOL Ltd., 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan

Carbonaceous chondrites mainly consist of chondrules and inclusions embedded in a fine-grained matrix. This texture is widely believed to have formed primarily by direct accretion of solar nebular materials, although it may have been modified to various extents by subsequent parent-body processes.

Recently, we studied all chondrules and inclusions larger than 400 μm in diameter and their rims (referred to as chondrules/rims) in the Mokoia CV3 carbonaceous chondrite using a scanning electron microscope, and found that the chondrules/rims experienced various degrees of aqueous alteration and that some also exhibit evidence of thermal metamorphism. The mineralogical and petrographic characteristics of the chondrules/rims suggest that the alteration and metamorphism occurred within the meteorite parent body. In contrast, however, the surrounding matrix does not show evidence of such alteration and metamorphism. These findings indicate that the alteration and metamorphism of the chondrules/rims did not occur in situ. Based on these results, we proposed a model that the chondrules/rims are actually clasts transported from regions in the parent body different from the location where the host meteorite was finally lithified.

If it can be assumed that the chondrules and inclusions studied are representative of all chondrules and inclusions in Mokoia, the results and interpretation pose a fundamental challenge regarding the formation of the whole Mokoia lithology; that is, it cannot be explained by either direct accretion of the solar nebula or conventional parent-body brecciation. We propose a model for the development of the Mokoia lithology through formation of chondrules/rims and fine matrix grains by fragmentation in different regions in the parent body, followed by transportation, mixing, and accumulation in a fluid state, and finally lithification of those objects. These processes may have been repeated, cyclically, within the parent body.

Reference
Tomeoka K, Ohnishi I (2015) Redistribution of chondrules in a carbonaceous chondrite parent body: A model. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.05.012]

Copyright Elsevier