John P. Bradley^a,b, Hope A. Ishii^a,b, Jeffrey J. Gillis-Davis^b, James Ciston^c, Michael H. Nielsen^d,e, Hans A. Bechtel^f, and Michael C. Martin^f

^aInstitute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550;
^bHawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822;
^cNational Center for Electron Microscopy,
^dMaterials Science Division, and
^eAdvanced Light Source Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720; and
^fDepartment of Materials Science and Engineering, University of California, Berkeley, CA 94720

The solar wind (SW), composed of predominantly ~1-keV H⁺ ions, produces amorphous rims up to ∼150 nm thick on the surfaces of minerals exposed in space. Silicates with amorphous rims are observed on interplanetary dust particles and on lunar and asteroid soil regolith grains. Implanted H⁺ may react with oxygen in the minerals to form trace amounts of hydroxyl (−OH) and/or water (H₂O). Previous studies have detected hydroxyl in lunar soils, but its chemical state, physical location in the soils, and source(s) are debated. If −OH or H₂O is generated in rims on silicate grains, there are important implications for the origins of water in the solar system and other astrophysical environments. By exploiting the high spatial resolution of transmission electron microscopy and valence electron energy-loss spectroscopy, we detect water sealed in vesicles within amorphous rims produced by SW irradiation of silicate mineral grains on the exterior surfaces of interplanetary dust particles. Our findings establish that water is a byproduct of SW space weathering. We conclude, on the basis of the pervasiveness of the SW and silicate materials, that the production of radiolytic SW water on airless bodies is a ubiquitous process throughout the solar system.

Reference
Bradley JP, Ishii HA, Gillis-Davis JJ, Ciston J, Nielsen MH, Bechtel HA and Martin MC (in press) Detection of solar wind-produced water in irradiated rims on silicate minerals. PNAS 111:1732–1735.
[doi:10.1073/pnas.1320115111]

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Anna Losiak^1,2, Eva Maria Wild³, Leonard Michlmayr³, Christian Koeberl^1,4

¹Department of Lithospheric Research, University of Vienna, Vienna, Austria
²Institute of Geological Sciences, Polish Academy of Sciences, Wrocław, Poland
³VERA Laboratory, Faculty of Physics, Isotope Research and Nuclear Physics, University of Vienna, Vienna, Austria
⁴Natural History Museum, Vienna, Austria

Rocks from drill cores LB-07A (crater fill) and LB-08A (central uplift) into the Bosumtwi impact crater, Ghana, were analyzed for the presence of the cosmogenic radionuclide ¹⁰Be. The aim of the study was to determine the extent to which target rocks of various depths were mixed during the formation of the crater-filling breccia, and also to detect meteoric water infiltration within the impactite layer. ¹⁰Be abundances above background were found in two (out of 24) samples from the LB-07A core, and in none of five samples from the LB-08A core. After excluding other possible explanations for an elevated ¹⁰Be signal, we conclude that it is most probably due to a preimpact origin of those clasts from target rocks close to the surface. Our results suggest that in-crater breccias were well mixed during the impact cratering process. In addition, the lack of a ¹⁰Be signal within the rocks located very close to the lake sediment–impactite boundary suggests that infiltration of meteoric water below the postimpact crater floor was limited. This may suggest that the infiltration of the meteoric water within the crater takes place not through the aerial pore-space, but rather through a localized system of fractures.

Reference
Losiak A, Wild EM, Michlmayr L and Koeberl C (in press) 10Be content in clasts from fallout suevitic breccia in drill cores from the Bosumtwi impact crater, Ghana: Clues to preimpact target distribution Meteoritics & Planetary Science
[doi:10.1111/maps.12256]
Published by arrangement with John Wiley & Sons

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Roger R. Fu, Bradford H. Hager, Anton I. Ermakov, Maria T. Zuber

Department of Earth, Atmospheric, and Planetary Sciences. Massachusetts Institute of Technology. Cambridge, MA

The asteroid Vesta is a differentiated planetesimal from the accretion phase of solar system formation. Although its present-day shape is dominated by a non-hydrostatic fossil equatorial bulge and two large, mostly unrelaxed impact basins, Vesta may have been able to approach hydrostatic equilibrium during a brief early period of intense interior heating. We use a finite element viscoplastic flow model coupled to a 1D conductive cooling model to calculate the expected rate of relaxation throughout Vesta’s early history. We find that, given sufficient non-hydrostaticity, the early elastic lithosphere of Vesta experienced extensive brittle failure due to self-gravity, thereby allowing relaxation to a more hydrostatic figure. Soon after its accretion, Vesta reached a closely hydrostatic figure with <2 km non-hydrostatic topography at degree-2, which, once scaled, is similar to the maximum disequilibrium of the hydrostatic asteroid Ceres. Vesta was able to support the modern observed amplitude of non-hydrostatic topography only >40-200 My after formation, depending on the assumed depth of megaregolith. The Veneneia and Rheasilvia giant impacts, which generated most non-hydrostatic topography, must have therefore occurred >40-200 My after formation. Based on crater retention ages, topography, and relation to known impact generated features, we identify a large region in the northern hemisphere that likely represents relic hydrostatic terrain from early Vesta. The long-wavelength figure of this terrain suggests that, before the two late giant impacts, Vesta had a rotation period of 5.02 hr (6.3% faster than present) while its spin axis was offset by 3.0 from that of the present. The evolution of Vesta’s figure shows that the hydrostaticity of small bodies depends strongly on its age and specific impact history and that a single body may embody both hydrostatic and non-hydrostatic terrains and epochs.

Reference
Fu RR, Hager BH, Ermakov AI and Zuber MT (2014) Efficient early global relaxation of asteroid Vesta. Icarus
[doi:10.1016/j.icarus.2014.01.023]
Copyright Elsevier

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Yuki Shiromoto¹, Hajime Susa¹, and Takashi Hosokawa²

¹Department of Physics, Konan University, Kobe 658-8501, Japan
²Department of Physics and Research Center for the Early Universe, The University of Tokyo, Tokyo 113-0033, Japan

The generation process of a magnetic field around a proto-first-star is studied. Utilizing the recent numerical results of proto-first-star formation based on radiation hydrodynamics simulations, we assess the magnetic field strength generated by the radiative force and the Biermann battery effect. We find that a magnetic field of ~10^-9 G is generated on the surface of the accretion disk around the proto-first-star. The field strength on the accretion disk is smaller by two orders of magnitude than the critical value, above which the gravitational fragmentation of the disk is suppressed. Thus, the generated seed magnetic field hardly affect the dynamics of on-site first star formation directly, unless an efficient amplification process is taken into consideration. We also find that the generated magnetic field is continuously blown out from the disk on the outflows to the poles, that are driven by the thermal pressure of photoheated gas. The strength of the diffused magnetic field in low-density regions is ~10^-14-10^-13 G at n_H = 10³ cm^-3, which could play an important role in the next generation star formation, as well as the seeds of the magnetic field in the present-day universe.

Reference
Shiromoto Y, Susa H and Takashi Hosokawa T (in press) Generation of Magnetic Field on the Accretion Disk around a Proto-first-star. The Astrophysical Journal 782:108.
[doi:10.1088/0004-637X/782/2/108]

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John T. Wasson^1,2 and Alan E. Rubin²

¹Institute of Geophysics and Planetary Physics, University of California Los Angeles, Los Angeles, California, USA
²Departments of Earth and Space Sciences and Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, California, USA

In numerous past papers, it was concluded that the fine (<1 μm) matrix immediately adjacent to, and radially symmetric around, chondrules in primitive chondrites consists of compact (low-porosity) rims that were attached in the solar nebula. We present here textural and compositional evidence that no matrix-like (or accretionary) rims around chondrules are present in the well-preserved CR2 chondrite LAP 02342. Fine-grained matrix-rich regions (i.e., candidate “rims”) at the edges of chondrules were studied with an electron-microprobe-based matrix-grid technique; comparison of the “rims” data for matrix regions near these chondrules showed the candidate “rims” to be compositionally heterogeneous, inconsistent with origins as radially symmetric, matrix-like rims formed by gradual accretion. This evidence (together with simulations and laboratory studies indicating that accretionary processes produced highly porous aggregates) strongly suggests that nebular processes did not produce compact matrix-like rims around chondrules in any chondrite group.

Reference
Wasson JT and Rubin AE (in press) Absence of matrix-like chondrule rims in CR2 LAP 02342. Meteoritics & Planetary Science
[doi:10.1111/maps.12237]
Published by arrangement with John Wiley & Sons

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Michael S. Kelley^a,1,2, Michael J. Gaffey^b,1, Vishnu Reddy^c,1, Juan A. Sanchez^d,1

^aDepartment of Geology and Geography, Georgia Southern University, Statesboro, Georgia 30460
^bDepartment of Space Studies, University of North Dakota, Grand Forks, North Dakota 58202
^cPlanetary Science Institute, Tucson, Arizona 85719
^dMax Planck Institute for Solar System Research, Katlenburg-Lindau, Germany
¹Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement No. NNX08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program.
²Currently at Science Mission Directorate, NASA Headquarters, Washington DC

Near-Earth asteroids (NEAs) are interesting as both a threat to the Earth and as the immediate sources for most meteorites. We observed NEA (4953) 1990 MU using the NASA Infrared Telescope Facility (IRTF) and University of Hawaii (UH) telescopes on Mauna Kea to constrain its surface composition and origin. The surface composition of 1990 MU is similar to ordinary chondrites (H chondrites). The calculated olivine and pyroxene chemistry of 1990 MU (Fa_13.5±1.3 and Fs_12.7±1.4) are consistent with the olivine and pyroxene chemistry ranges for H chondrites (Fa_15-21 and Fs_13-19) (Dunn et al. 2010), although the estimated Fa value is at the lower end of H chondrite range. The olivine abundance ratio of 1990 MU (0.57±0.03) is slightly higher but not inconsistent with H chondrites (0.47-0.55±0.03). The radar circular polarization ratio (same circular polarization state or SC/opposite circular polarization state or OC) (Benner et al. 2008) of 1990 MU is 0.36±0.03, which is higher than the mean SC/OC ratio for S-type NEAs (0.270±0.079). 1990 MU SC/OC value is also higher than those of (25143) Itokawa (0.27±0.04), (4179) Toutatis (0.29±0.01) and (433) Eros (0.28±0.06) suggesting a rougher surface at decimeter scale (Benner et al. 2008). We constrained the diameter of 1990 MU (4.4 km) using the average albedo at 0.55 μm of H chondrites (0.21) and absolute magnitude (H) of 14.1 (Flower and Chillemi, 1992). This diameter is higher than the 2.8 km value from Harris et al. (2011) using an albedo of 0.52 for 1990 MU. This albedo value is unusually high for H chondrites, which have an albedo range of 0.12-0.30. We compared olivine and pyroxene chemistries of 1990 MU with main belt asteroid (6) Hebe, probable parent body of H chondrite meteorites and IIE irons (Gaffey and Gilbert, 1998), and found that 1990 MU has more high-calcium pyroxene than Hebe. Fayalite and ferrosilite values of the two asteroids are consistent with H chondrites but don’t overlap each other. The differences could be due to compositional variations observed on Hebe by Gaffey and Gilbert (1998), although the observed rotational variation in spectral parameters does not match well with those of 1998 MU.

Reference
Kelley MS, Gaffey MJ, Reddy V and Sanchez JA (2014) Surface Composition of Near-Earth Asteroid (4953) 1990 MU: Possible Fragment of (6) Hebe. Icarus
[doi:10.1016/j.icarus.2014.01.015]
Copyright Elsevier

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Richard C. Greenwood^a, Jean-Alix Barrat^b, Akira Yamaguchi^c, Ian A. Franchi^a, Edward R.D. Scott^d, William F. Bottke^e, Jenny M. Gibson^a

^aPlanetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
^bCNRS UMR 6538 (Domaines Océaniques), U.B.O.-I.U.E.M., Place Nicolar Copernic, 29280 Plouzané Cedex, France
^cNational Institute of Polar Research, Tokyo 190-8518, Japan
^dHawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, HI 96822, USA
^eSouthwest Research Institute and NASA Lunar Science Institute, 1050 Walnut Street, Suite 400, Boulder, CO 80302, USA

Oxygen isotope measurements of a suite of 22 diogenites demonstrate that they have a restricted range of Δ¹⁷O values: . These results indicate that the diogenites form a single population consistent with a single parent body source, rather than multiple sources as has recently been suggested. Our previously published analysis of eucrites and cumulate eucrites (n=34) give very similar results to the diogenites, with  and confirm that diogenites and eucrites are from the same parent asteroid. The isotopic homogeneity displayed by diogenites, eucrites and cumulate eucrites, provides strong evidence for an early large-scale melting event on the HED parent body, possibly resulting in the formation of a magma ocean. The paradox, whereby diogenites show isotopic evidence in favor of global melting, but also geochemical features indicative of late stage interaction with eucritic crust, may reflect a rapid transition from global to serial magmatism on their parent body. The fact that all the lithologically varied HED units have an isotopically homogeneous composition supports the proposal that they are derived from a single, large, diverse asteroid, most likely 4 Vesta. The recent suggestion that the HEDs are not from Vesta, but instead represent material from the same asteroidal source as the main-group pallasites and IIIAB irons can be excluded by our oxygen isotope data.

Reference
Greenwood RC, Barrat J-A, Yamaguchi A, Franchi IA, Scott ERD, Bottke WF and Gibson JM (2014) The oxygen isotope composition of diogenites: Evidence for early global melting on a single, compositionally diverse, HED parent body. Earth and Planetary Science Letters 390:165–174.
[doi:10.1016/j.epsl.2013.12.011]
Copyright Elsevier

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Pasquale Tricarico

Planetary Science Institute, Tucson, AZ 85719, USA

The hydrostatic equilibrium of multi-layer bodies lacks a satisfactory theoretical treatment despite its wide range of applicability. Here we show that by using the exact analytical potential of homogeneous ellipsoids we can obtain recursive analytical solutions and an exact numerical method for the hydrostatic equilibrium shape problem of multi-layer planets and synchronous moons. The recursive solutions rely on the series expansion of the potential in terms of the polar and equatorial shape eccentricities, while the numerical method uses the exact potential expression. These solutions can be used to infer the interior structure of planets and synchronous moons from their observed shape, rotation, and gravity. When applied to the dwarf planet Ceres, we show that it is most likely a differentiated body with an icy crust of equatorial thickness 30-90 km and a rocky core of density 2.4-3.1 g cm^-3. For synchronous moons, we show that the J₂/C₂₂  10/3 and the (b – c)/(a – c)  1/4 ratios have significant corrections of order Ω²/(πGρ), with important implications for how their gravitational coefficients are determined from fly-by radio science data and for how we assess their hydrostatic equilibrium state.

Reference
Tricarico P (2014) Multi-layer Hydrostatic Equilibrium of Planets and Synchronous Moons: Theory and Application to Ceres and to Solar System Moons. The Astrophysical Journal 782:99.
[doi:10.1088/0004-637X/782/2/99]

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Stephen M. Elardo^1,*, Charles K. Shearer Jr.¹, Amy L. Fagan^2,3, Lars E. Borg⁴, Amy M. Gaffney⁴, Paul V. Burger¹, Clive R. Neal², Vera A. Fernandes⁵, Francis M. McCubbin¹

¹Department of Earth & Planetary Sciences, Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, USA
²Department of Civil & Environmental Engineering & Earth Sciences, University of Notre Dame, Notre Dame, Indiana, USA
³Lunar & Planetary Institute, USRA, Houston, Texas, USA
⁴Chemical Sciences Division, Lawrence Livermore National Laboratory, Livermore, California, USA
⁵Museum für Naturkunde- Berlin, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany

Northwest Africa (NWA) 4734 is an unbrecciated basaltic lunar meteorite that is nearly identical in chemical composition to basaltic lunar meteorites NWA 032 and LaPaz Icefield (LAP) 02205. We have conducted a geochemical, petrologic, mineralogic, and Sm-Nd, Rb-Sr, and Ar-Ar isotopic study of these meteorites to constrain their petrologic relationships and the origin of young mare basalts. NWA 4734 is a low-Ti mare basalt with a low Mg* (36.5) and elevated abundances of incompatible trace elements (e.g., 2.00 ppm Th). The Sm-Nd isotope system dates NWA 4734 with an isochron age of 3024 ± 27 Ma, an initial ε_Nd of +0.88 ± 0.20, and a source region ¹⁴⁷Sm/¹⁴⁴Nd of 0.201 ± 0.001. The crystallization age of NWA 4734 is concordant with those of LAP 02205 and NWA 032. NWA 4734 and LAP 02205 have very similar bulk compositions, mineral compositions, textures, and ages. Their source region ¹⁴⁷Sm/¹⁴⁴Nd values indicate that they are derived from similar, but distinct, source materials. They probably do not sample the same lava flow, but rather are similarly sourced, but isotopically distinct, lavas that probably originate from the same volcanic complex. They may have experienced slightly different assimilation histories in route to eruption, but can be source-crater paired. NWA 032 remains enigmatic, as its source region ¹⁴⁷Sm/¹⁴⁴Nd definitively precludes a simple relationship with NWA 4734 and LAP 02205, despite a similar bulk composition. Their high Ti/Sm, low (La/Yb)_N, and Cl-poor apatite compositions rule out the direct involvement of KREEP. Rather, they are consistent with low-degree partial melting of late-formed LMO cumulates, and indicate that the geochemical characteristics attributed to urKREEP are not unique to that reservoir. These and other basaltic meteorites indicate that the youngest mare basalts originate from multiple sources, and suggest that KREEP is not a prerequisite for the most recent known melting in the Moon.

Reference
Elardo SM, Shearer CK, Fagan AL, Borg LE, Gaffney AM, Burger PV, Neal CR, Fernandes VA and McCubbin FM (in press) The origin of young mare basalts inferred from lunar meteorites Northwest Africa 4734, 032, and LaPaz Icefield 02205. Meteoritics & Planetary Science
[doi:10.1111/maps.12239]
Published by arrangement with John Wiley & Sons

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Ann M. Ollila¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Princeton University, Princeton, NJ 08540, USA

The ChemCam instrument package on the Mars rover, Curiosity, provides new capabilities to probe the abundances of certain trace elements in the rocks and soils on Mars using the laser-induced breakdown spectroscopy technique. We focus on detecting and quantifying Li, Ba, Rb, and Sr in targets analyzed during the first 100 sols, from Bradbury Landing Site to Rocknest. Univariate peak area models and multivariate partial least squares models are presented. Li, detected for the first time directly on Mars, is generally low (<15 ppm). The lack of soil enrichment in Li, which is highly fluid mobile, is consistent with limited influx of subsurface waters contributing to the upper soils. Localized enrichments of up to ~60 ppm Li have been observed in several rocks but the host mineral for Li is unclear. Bathurst_Inlet is a fine-grained bedrock unit in which several analysis locations show a decrease in Li and other alkalis with depth, which may imply that the unit has undergone low-level aqueous alteration that has preferentially drawn the alkalis to the surface. Ba (~1000 ppm) was detected in a buried pebble in the Akaitcho sand ripple and it appears to correlate with Si, Al, Na, and K, indicating a possible feldspathic composition. Rb and Sr are in the conglomerate Link at abundances >100 ppm and >1000 ppm, respectively. These analysis locations tend to have high Si and alkali abundances, consistent with a feldspar composition. Together, these trace element observations provide possible evidence of magma differentiation and aqueous alteration.

Reference
Ann M. Ollila et al. (in press) Trace element geochemistry (Li, Ba, Sr, and Rb) using Curiosity’s ChemCam: Early results for Gale crater from Bradbury Landing Site to Rocknest. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004517]
Published by arrangement with John Wiley & Sons

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