¹A.Raponi et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.02.001]
INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, Rome I-00133, Italy
Copyright Elsevier

Occator Crater on dwarf planet Ceres hosts the so-called faculae, several areas with material 5 to 10 times the albedo of the average Ceres surface: Cerealia Facula, the brightest and largest, and several smaller faculae, Vinalia Faculae, located on the crater floor. The mineralogy of the whole crater is analyzed in this work. Spectral analysis is performed from data of the VIR instrument on board the Dawn spacecraft. We analyse spectral parameters of all main absorption bands, photometry, and continuum slope. Because most of the absorption features are located in a spectral range affected by thermal emission, we developed a procedure for thermal removal. Moreover, quantitative modeling of the measured spectra is performed with a radiative transfer model in order to retrieve abundance and grain size of the identified minerals. Unlike the average Ceres surface that contains a dark component, Mg–Ca-carbonate, Mg-phyllosilicates, and NH4-phyllosilicates, the faculae contain mainly Na-carbonate, Al-phyllosilicates, and NH4-chloride. The present work establishes unambiguously the presence of NH4-chloride thanks to the high-spatial resolution data. Vinalia and Cerealia Faculae show significant differences in the concentrations of these minerals, which have been analyzed. Moreover, heterogeneities are also found within Cerealia Facula that might reflect different deposition events of bright material. An interesting contrast in grain size is found between the center (10–60 µm) and the crater floor/peripheral part of the faculae (100–130 µm), pointing to different cooling time of the grains, respectively faster and slower, and thus to different times of emplacement. This implies the faculae formation is more recent than the crater impact event, consistent with other observations reported in this special issue. For some ejecta, we derived larger concentrations of minerals producing the absorption bands, and smaller grains with respect to the surrounding terrain. This may be related to heterogeneities in the material pre-existent to the impact event.

^1,2Quinn R. Shollenberger, ²Lars E. Borg, ¹Jan Render, ¹Samuel Ebert, ¹Addi Bischoff, ³Sara S. Russell, ¹Gregory A. Brennecka
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.02.006]
¹Institut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, Münster 48149 Germany
²Nuclear & Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue L-231, Livermore, CA 94550 USA
³Department of Earth Sciences, Natural History Museum, Cromwell Road, Kensington, London SW7 5BD, UK
Copyright Elsevier

Calcium-aluminum-rich inclusions (CAIs) are the oldest dated materials in the Solar System and numerous previous studies have revealed nucleosynthetic anomalies relative to terrestrial rock standards in many isotopic systems. However, most of the isotopic data from CAIs has been limited to the Allende meteorite and a handful of other CV3 chondrites. To better constrain the isotopic composition of the CAI-forming region, we report the first Sr, Mo, Ba, Nd, and Sm isotopic compositions of two CAIs hosted in the CK3 desert meteorites NWA 4964 and NWA 6254 along with two CAIs from the CV3 desert meteorites NWA 6619 and NWA 6991. After consideration of neutron capture processes and the effects of hot-desert weathering, the Sr, Mo, Ba, Nd, and Sm stable isotopic compositions of the samples show clearly resolvable nucleosynthetic anomalies that are in agreement with previous results from Allende and other CV meteorites. The extent of neutron capture, as manifested by shifts in the observed ¹⁴⁹Sm-¹⁵⁰Sm isotopic composition of the CAIs is used to estimate the neutron fluence experienced by some of these samples and ranges from 8.40×10¹³ to 2.11×10¹⁵ n/cm². Overall, regardless of CAI type or host meteorite, CAIs from CV and CK chondrites have similar nucleosynthetic anomalies within analytical uncertainty. We suggest the region that CV and CK CAIs formed was largely uniform with respect to Sr, Mo, Ba, Nd, and Sm isotopes when CAIs condensed and that CAIs hosted in CV and CK meteorites are derived from the same isotopic reservoir.

¹Abigail A. Fraeman
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2018JE005535]
¹Jet Propulsion Laboratory, California Institute of Technology
Published by arrangement with John Wiley & Sons

Mittlefehldt et al. [2018] synthesize APXS chemical measurements along more than 4.5 km of Endeavour crater’s rim. Their analyses clarify details of Endeavour’s geologic history, including evidence for three to four distinct episodes of aqueous alteration. Fracture driven aqueous systems and Mn mobility are particularly important both here and at Curiosity’s landing site on the opposite side of the planet. The detailed documentation of APXS data products within this paper will be a key reference for researchers who want to perform future work on questions related to Mars aqueous geochemistry, impact processes, and Martian crustal and atmospheric evolution.

¹David W. Mittlefehldt et al. (>10)
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2017JE005474]
¹Mail code XI3, Astromaterials Research Office, NASA/Johnson Space Center, Houston, TX, USA
Published by arrangement with John Wiley & Sons

We report the results of geological studies by the Opportunity Mars rover on the Endeavour Crater rim. Four major units occur in the region (oldest to youngest): the Matijevic, Shoemaker, Grasberg and Burns formations. The Matijevic formation, consisting of fine-grained clastic sediments, is the only pre-Endeavour-impact unit and might be part of the Noachian etched units of Meridiani Planum. The Shoemaker formation is a heterogeneous polymict impact breccia; its lowermost member incorporates material eroded from the underlying Matijevic formation. The Shoemaker formation is a close analog to the Bunte Breccia of the Ries Crater, although the average clast sizes are substantially larger in the latter. The Grasberg formation is a thin, fine-grained, homogeneous sediment unconformably overlying the Shoemaker formation, and likely formed as an airfall deposit of unknown areal extent. The Burns formation sandstone overlies the Grasberg, but compositions of the two units are distinct; there is no evidence that the Grasberg formation is a fine-grained subfacies of the Burns formation. The rocks along the Endeavour Crater rim were affected by at least four episodes of alteration in the Noachian and Early Hesperian: (i) vein formation and alteration of pre-impact Matijevic formation rocks; (ii) low-water/rock alteration along the disconformity between the Matijevic and Shoemaker formations; (iii) alteration of the Shoemaker formation along fracture zones; and (iv) differential mobilization of Fe and Mn, and CaSO4-vein formation in the Grasberg and Shoemaker formations. Episodes (ii) and (iii) possibly occurred together, but (i) and (iv) are distinct from either of these.

^1,2Penelope J. Wozniakiewicz,^3,4Anton T. Kearsley,¹Mark J. Burchell,¹Mark C. Price,⁵Hope A. Ishii,¹Michael J. Cole
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13052]
¹School of Physical Science, University of Kent, Canterbury, UK
²Department of Earth Sciences, Natural History Museum, London, UK
³North Yorkshire, UK
⁴Imaging and Analysis Centre, Natural History Museum, London, UK
⁵Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, Hawai’i, USA
Published by arrangement with John Wiley & Sons

Over the last decade, silica aerogel tracks and aluminum foil craters on the Stardust collector have been studied extensively to determine the nature of captured cometary dust grains. Analysis of particles captured in aerogel has been developed to a fine art, aided by sophisticated preparation techniques, and yielding revolutionary knowledge of comet dust mineralogy. The Stardust foil craters can be interpreted in terms of impacting particle size and structure, but almost all studies of composition for their contents have relied on in situ analysis techniques or relatively destructive extraction of materials. This has limited their examination and interpretation. However, numerous experimental hypervelocity impact studies under Stardust-Wild 2 encounter conditions have shown that abundant dust components are preserved in foil craters of all sizes. Using some of these analogue materials, we have previously shown that modern, nondestructive scanning electron microscope imaging and X-ray microanalysis techniques can document distribution of dust remnants both quickly and thoroughly within foil craters prior to any preparation. Here we present findings from our efforts to quantify the amount of residue and demonstrate a simple method of crater shape modification which can bring material into positions where it is much more accessible for in situ analysis, or safe removal of small subsamples. We report that approximately 50% of silicate-dominated impactors were retained as impact crater residue; however, <3% of organic impactors remained in the craters after impact.

¹L. A. Taylor,²J. V. Hogancamp,³L. A. Watts,⁴S. J. Wentworth,⁴P. D. Archer,⁵R. A. Zeigler,⁶A. Basu
Meteoritics & Planetary Science (in Press) Links to Article [DOI: 10.1111/maps.13060]

¹Department of Earth and Planetary Sciences, Planetary Geoscience Institute, University of Tennessee, Knoxville, Tennessee, USA
²Geocontrols Systems—Jacobs JETS Contract, NASA Johnson Space Center, Houston, Texas, USA
³Barrios Technology—Jacobs JETS Contract, NASA Johnson Space Center, Houston, Texas, USA
⁴Jacobs, NASA Johnson Space Center, Houston, Texas, USA
⁵Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, Texas, USA
⁶Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, Indiana, USA
Published by arrangement with John Wiley & Sons

Lunar samples provide ground-truth for all planetary exploration. Lunar soils, especially their <1 mm fraction, constitute the only primary standards for remotely sensing the composition of small airless planetary bodies. Therefore, maintaining the integrity, especially of the <1 mm fraction, takes on a much larger, big picture responsibility. A possibility has been suggested that lunar soils may disintegrate (to smaller grain sizes) if exposed to the Earth’s moist atmosphere, thus losing some of their intrinsic value to science. We have tested that possibility by multiple, independent reanalyses with three techniques (wet-sieving in water and in alcohol, and laser diffractometry) using a fresh allocation of Apollo 17 “orange soil,” 74220. Our results are very similar to each other despite repeated soaking–drying in water, and also to those originally determined in the 1970s. We have also used a laser diffractometry technique to reanalyze the grain sizes of ~50 mg splits of eight soils that were initially analyzed three to four decades ago. The results are randomly different from previous measurements, which we attribute to nonrepresentative subsampling of very small amounts from previous allocations; ~50 mg is too small for obtaining representative aliquots. The results of grain-size analyses presented and discussed in this study indicate that the integrity of the lunar soil 74220, and indeed, all lunar soils, has not been physically compromised in the last four decades.

^1,2,3Yingzhuo Jia, ¹Yongliao Zou, ¹Jinsong Ping, ²Changbin Xue, ¹Jun Yan, ⁴Yuanming Ning
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2018.02.011]
¹National Astronomical Observatories, Chinese Academy of Science, Beijing, 100012, China
²National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
³University of Chinese Academy of Sciences, Beijing, 100049, China
⁴Lunar Exploration and Aerospace Engineering Center, Beijing, 100028, China

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Christian Carli,^2,3Giovanni Pratesi,³Vanni Moggi-Cecchi,¹Francesca Zambon,¹Fabrizio Capaccioni,²Simone Santoro
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.13056]
¹IAPS-INAF, Rome, Italy
²Department of Earth Science, University of Florence, Florence, Italy
³Natural History Museum of University of Florence, Florence, Italy
Published by arrangement with John Wiley & Sons

Visible and near-infrared (VNIR) reflectance is an important spectroscopic technique to identify minerals, and their associations, on planetary body surfaces. Howardites, eucrites, and diogenites (HED) are a class of igneous-like meteorites whose genetic connection with asteroid 4 Vesta has since long been inferred and recently confirmed by Dawn mission results. Pyroxene and olivine are the two major mafic minerals present in HED which can be identified with VNIR reflectance measurements. Thus, studying the compositional variability of those phases and their mixtures by means of laboratory spectroscopic measurements on different diogenitic or eucritic samples is one of the prime methods to better understand the evolution of 4 Vesta’s crust. Here, we report the VNIR reflectance spectral analysis of a harzburgitic olivine diogenite, Northwest Africa 6232 (probably paired with Northwest Africa 5480), containing variable amounts of olivine as small grains or aggregates. We found that the olivine diogenite spectral parameters (e.g., band position) of powdered samples and polished slabs are in agreement. Moreover, the olivine diogenite band position shifts from synthetic orthopyroxene in accordance with the presence of olivine and chromite. In particular, the presence of a large olivine clast permits us to determine a linear variation of the band position from synthetic orthopyroxene and olivine, but underestimates the presence of olivine in the olivine diogenite spot.

¹D.P. Moriarty III,²C. M. Pieters
Journal of Geophysical Research, Planets (in Press) Link to Article [DOI: 10.1002/2017JE005364]
¹Planetary Geology, Geophysics, and Geochemistry Laboratory, NASA GSFC, Greenbelt, MD
²Department of Earth, Environmental, and Planetary Sciences, Brown University, Providence, RI
Published by arrangement with John Wiley & Sons

Using Moon Mineralogy Mapper data, we characterize surface diversity across the enormous South Pole – Aitken Basin (SPA) by evaluating the abundance and composition of pyroxenes, which are overwhelmingly the most abundant mafic mineral in the region. Although SPA exhibits significant complexity due to billions of years of geologic processes subsequent to formation, the basin has retained regular patterns of compositional heterogeneity across its structure. Four distinct, roughly concentric zones are defined: (1) a central SPA compositional anomaly (SPACA), which exhibits a pervasive elevated Ca,Fe-rich pyroxene abundance, (2) a Mg-Pyroxene Annulus, which is dominated by abundant Mg-rich pyroxenes, (3) a Heterogeneous Annulus, which exhibits localized pyroxene-rich areas spatially mixed with feldspathic materials, and (4) the SPA Exterior, which is primarily feldspathic. Pyroxene compositions in the Heterogeneous Annulus are similar to those in the Mg-Pyroxene Annulus, and Mg-rich pyroxenes also underlie the more Ca,Fe-rich pyroxene surface material across SPACA. The establishment of these four distinct compositional zones across SPA constrains future basin evolution models serves to guide potential sample return (and other science) targets.

¹M. Boyet, ²A. Bouvier, ¹P. Frossard, ¹T. Hammouda, ³M. Garçon, ¹A. Gannoun
Earth and Planetary Science Letters 488, 68-78 Link to Article [https://doi.org/10.1016/j.epsl.2018.02.004https://doi.org/10.1016/j.epsl.2018.02.004]
¹Laboratoire Magmas et Volcans, Université Clermont Auvergne, France
²Department of Earth Sciences, Centre for Planetary Science and Exploration, University of Western Ontario, London, Canada
³Department of Earth Sciences, ETH Zurich, Switzerland
Copyright Elsevier

The 146Sm–142Nd extinct decay scheme (146Sm half-life of 103 My) is a powerful tool to trace early Earth silicate differentiation. Differences in 142Nd abundance measured between different chondrite meteorite groups and the modern Earth challenges the interpretation of the 142Nd isotopic variations found in terrestrial samples because the origin of the Earth and the nature of its building blocks is still an ongoing debate. As bulk meteorites, the enstatite chondrites (EC) have isotope signatures that are the closest to the Earth value with an average small deficit of ∼10 ppm in 142Nd relative to modern terrestrial samples. Here we review all the Nd isotope data measured on EC so far, and present the first measurements on an observed meteorite fall Almahata Sitta containing pristine fragments of an unmetamorphosed enstatite chondrite belonging to the EL3 subgroup. Once 142Nd/144Nd ratios are normalized to a common chondritic evolution, samples from the EC group (both EL and EH) have a deficit in 142Nd but the dispersion is important (μ142Nd=−10±12 (2SD) ppm). This scatter reflects their unique mineralogy associated to their formation in reduced conditions (low fO2 or high C/O). Rare-earth elements are mainly carried by the sulfide phase oldhamite (CaS) that is more easily altered than silicates by weathering since most of the EC meteorites are desert finds. The EL6 have fractionated rare-earth element patterns with depletion in the most incompatible elements. Deviations in Nd mass independent stable isotope ratios in enstatite chondrites relative to terrestrial standard are not resolved with the level of analytical precision achieved by modern mass spectrometry techniques. Here we show that enstatite chondrites from the EL3 and EL6 subgroups may come from different parent bodies. Samples from the EL3 subgroup have Nd (μ142Nd=−0.8±7.0, 2SD) and Ru isotope ratios undistinguishable from that of the Bulk Silicate Earth. EL3 samples have never been analyzed for Mo isotopes. Because these enstatite chondrites are relatively small in size and number, they are usually not available for destructive isotopic measurements. Average values based on the measurement of EL6 samples should not be considered as representative of the whole EL group because of melting and thermal metamorphism events affecting the Sm/Nd ratios and prolonged open-system history. The EL3 chondrites are the best candidates as the Earth’s building blocks. These new results remove the need to change the composition of refractory incompatible elements early in Earth’s history.