K.R. Bermingham^a,b, K. Mezger^a,c, S.J. Desch^d, E.E. Scherer^a, M. Horstmann^e

^aInstitut für Mineralogie, Westfälische Wilhelms-Universität, Corrensstraße 24, Münster, 48149, Germany
^bIsotope Geochemistry Laboratory, Department of Geology, University of Maryland, College Park, MD-20742 USA
^cInstitut für Geologie, Universität Bern, Baltzerstrasse 1 + 3, 3012 Bern, Switzerland
^dSchool of Earth and Space Exploration, Arizona State University, P.O. Box 871404, Tempe, AZ-85287-1404 USA
^eInstitut für Planetologie, Westfälische Wilhelms-Universität, Wilhelm-Klemm-Straße 10, Münster, 48149, Germany

The abundance and distribution of isotopes throughout the Solar System can be used to constrain the number and type of nucleosynthetic events that contributed material to the early nebula. Barium is particularly well suited to quantifying the degree of isotope heterogeneity in the Solar System because it comprises seven stable isotopes that were synthesized by three different nucleosynthetic processes (s-, r-, and p-processes), all of which contributed material to the Solar System. There is also potential contribution to ¹³⁵Ba from short-lived radioisotope ¹³⁵Cs, conclusive evidence for which is yet to be reported. Four Allende (CV3) Ca,Al-rich inclusions (CAI 1, CAI 2, CAI 4, CAI 5) and one Allende dark inclusion (DI) were analyzed for Ba isotope variability. Two CAIs (CAI 2 and CAI 5) display ¹³⁵Ba excesses that are not accompanied by ¹³⁷Ba anomalies. Calcium-aluminium-rich inclusion 1 displays a ¹³⁵Ba excess that is possibly coupled with a ¹³⁷Ba excess, and the remaining refractory inclusions (CAI 2 and DI) have terrestrial Ba isotope compositions. These Ba isotope data are presented in conjunction with published whole rock Ba isotope data from individual Allende CAIs. The enrichment in ¹³⁵Ba and absence of coupled ¹³⁷Ba excesses in CAI 2 and CAI 5 is interpreted to indicate that the anomalies are not purely nucleosynthetic in origin but also contain contributions (16 – 48 ppm) from the decay of short-lived ¹³⁵Cs. The majority of Allende CAIs studied to date may also have similar contributions from ¹³⁵Cs on the basis of higher than expected ¹³⁵Ba excesses if the Ba isotope anomalies were purely nucleosynthetic in origin. The ¹³⁵Ba anomalies appear not to be coupled with superchondritic Cs/Ba, which may imply that the contribution to ¹³⁵Ba did not occur via in situ decay of live ¹³⁵Cs. However, it is feasible that the CAIs had a superchondritic Cs/Ba during decay of ¹³⁵Cs, but Cs was subsequently removed from the system during aqueous alteration on the parent body. An alternative scenario is the potential existence of a transient high-temperature reservoir having superchondritic Cs/Ba in the early Solar System while ¹³⁵Cs was extant, which enabled a radiogenic ¹³⁵Ba signature to develop in some early condensates. The nucleosynthetic source of ¹³⁵Cs can be determined by reconciling the predicted astrophysical ¹³⁵Cs abundance with its measured abundance in meteorites. The currently accepted initial¹³⁵Cs/¹³³Cs of the Solar System, [¹³⁵Cs/¹³³Cs]₀, may be underestimated because the spread of Cs/Ba among samples is small and the range of excess ¹³⁵Ba is limited thus leading to inaccuracies when estimating [¹³⁵Cs/¹³³Cs]₀. If the initial meteoritic abundance of ¹³⁵Cs was indeed higher than is currently thought, the most probable stellar source of short-lived radioisotopes was a nearby core-collapse supernova and/or the Wolf-Rayet wind driven by its progenitor.

Reference
Bermingham KR, Mezger K, Desch SJ, Scherer EE and Horstmann M (in press) Evidence for extinct 135Cs from Ba isotopes in Allende CAIs? Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2013.12.016]
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A. Morlok^a,b, C. Lisse^c, A.B. Mason^d, E. Bullock^e, M.M. Grady^a,f

^aDepartment of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
^bCurrent address: Institut für Planetologie, WWU Münster, Wilhelm-Klemm-Straße 10, 48149, Münster, Germany
^cThe Johns Hopkins University Applied Physics Laboratory,11100 Johns Hopkins Road, Laurel, MD 20723, USA
^dFinnish Centre for Astronomy with ESO (FINCA), University of Turku, Tuorla Observatory, Väisäläntie 20, FI-21500 PIIKKIÖ, Finland
^eSmithsonian Institution PO Box 37012, MRC 119 Washington, DC 20013-7012, USA
^fDepartment of Physical Sciences, The Open University, Walton Hall, MK7 6AA Milton Keynes, UK

We obtained mid-infrared spectra of chondrules, matrix, CAIs and bulk material from primitive type 1-4 chondrites in order to compare them with the dust material in young, forming solar systems and around comets. Our aim is to investigate whether there are similarities between the first processed materials in our early Solar System and protoplanetary disks currently forming around other stars. Chondrule spectra can be divided into two groups. 1) Chondrules dominated by olivine features at ∼11.3 μm and ∼10.0 μm. 2) mesostasis rich chondrules that show main features at ∼10 μm. Bulk ordinary chondrites show similar features to both groups.
Fine-grained matrix is divided into three groups. 1) phyllosilicate-rich with a main band at ∼10μm, 2) olivine-rich with bands at 11.3 μm and ∼10 μm, 3) pyroxene–rich with several peaks between 9.3 μm and 11.2 μm. Impact shock processed matrix from Murchison (CM2) shows features from phyllosilicate-rich, amorphous and olivine–rich material. CAIs show melilite/spinel –rich features between 10.2 μm and 12.5 μm.
Astronomical spectra are divided into four groups based on their spectral characteristics – amorphous (group 1), pyroxene-rich (group 2), olivine–rich (group 3) and ‘complex’ (group 4). Group 2 is similar to enstatite-rich fine grained material like e.g. Kakangari (K3) matrix. Group 3 and 4 can be explained by a combination of varying concentrations of olivine and mesostasis-rich chondrules and fine-grained matrix, but also show very good agreement with shock processed material. Comparison of band ratios confirms the similarity with chondritic material e.g. for HD100546, while the inner disk of HD142527 show no sign of chondrule material.
Comparison between the laboratory infrared-red IR data and astronomical spectra indicate a general similarity between primitive solar system materials and circumstellar dust and comets, especially in the inner disks of young solar systems. However, other amorphous materials like IDP/GEMS have to be taken into account.

Reference
Morlok A, Liss C, Mason AB, Bullock E and Grady MM (in press) Mid-Infrared Spectroscopy of Components in Chondrites: Search for Processed Materials in Young Solar Systems and Comets. Icarus
[doi:10.1016/j.gca.2013.12.020]
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Edward R. D. Scott

Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI, USA

This is an announcement without abstract.

Reference
Scott ERD (in press) Handbook of Iron Meteorites by Vagn F. Buchwald, 1975: Electronic edition. Meteoritics & Planetary Science 48:2608.
[doi:10.1111/maps.12232]
Published by arrangement with John Wiley & Sons

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Heng Chen¹, Bach Mai Nguyen¹ and Frédéric Moynier^1,2,*

¹Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, Missouri, USA
²Institut de Physique du Globe de Paris, Université Paris Diderot, Paris, France

High-precision Zn isotopic compositions measured by MC-ICP-MS are documented for 32 iron meteorites from various fractionally crystallized and silicate-bearing groups. The δ⁶⁶Zn values range from −0.59‰ up to +5.61‰ with most samples being slightly enriched in the heavier isotopes compared with carbonaceous chondrites (0 < δ⁶⁶Zn < 0.5). The δ⁶⁶Zn versus δ⁶⁸Zn plot of all samples defines a common linear fractionation line, which supports the hypothesis that Zn was derived from a single reservoir or from multiple reservoirs linked by mass-dependent fractionation processes. Our data for Redfields fall on a mass fractionation line and therefore refute a previous claim of it having an anomalous isotopic composition due to nonmixing of nucleosynthetic products. The negative correlation between δ⁶⁶Zn and the Zn concentration of IAB and IIE is consistent with mass-dependent isotopic fractionation due to evaporation with preferential loss of lighter isotopes in the vapor phase. Data for the Zn concentrations and isotopic compositions of two IVA samples demonstrate that volatile depletion in the IVA parent body is not likely the result of evaporation. This is important evidence that favors the incomplete condensation origin for the volatile depletion of the IVA parent body.

Reference
Chen H, Nguyen BM and Moynier F (2013) Zinc isotopic composition of iron meteorites: Absence of isotopic anomalies and origin of the volatile element depletion. Meteoritics & Planetary Science 48:2441–2450.
[doi:10.1111/maps.12229]
Published by arrangement with John Wiley & Sons

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Michail I. Petaev^a,b, Shichun Huang^a, Stein B. Jacobsen^a and Alan Zindler^a

^aDepartment of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138; and
^bSolar, Stellar, and Planetary Sciences, Harvard–Smithsonian Center for Astrophysics, Cambridge, MA 02138

Besides providing additional arguments against the Pt depositing event (1) as a cause of the Younger Dryas cooling, Boslough’s letter (2) raises an important question about the scale of this event. Indeed, a localized deposition of Pt by the Cape York meteorite shower is an attractive hypothesis considered by us initially (3), but abandoned because of (i) a large difference in the …

Reference
Petaev MI, Huang S, Jacobsen SB and Zindler A (2013) Reply to Boslough: Is Greenland Pt anomaly global or local?. PNAS 110:E5036.
[doi:10.1073/pnas.1320772111]

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Mark Boslough

Sandia National Laboratories, Albuquerque, NM 87185

Petaev et al. (1) tested the suite of hypotheses (collectively known as the “impact hypothesis”) that a swarm of impacts or airbursts from comets, chondritic, or stony asteroids caused an abrupt climate change, continental-scale wildfires, mass extinctions, and collapse of the Clovis culture at or near the Younger Dryas Boundary (YDB). The authors identify a large Pt anomaly in the Greenland Ice Sheet Project 2 (GISP2) core and suggest that it hints at an extraterrestrial source. Because there is no corresponding Ir spike, Petaev et al. challenge the impact hypothesis by proposing a highly fractionated iron meteorite. The Pt anomaly predates ammonimum and nitrate peaks in the GISP2 core by decades, eliminating …

Reference
Boslough M (2013) Greenland Pt anomaly may point to noncataclysmic Cape York meteorite entry. PNAS 110:E5035.
[doi:10.1073/pnas.1320328111]

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T. Sabri¹, L. Gavilan², C. Jäger¹, J. L. Lemaire², G. Vidali^2,5, H. Mutschke³ and T. Henning⁴

¹Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany
²Observatoire de Paris/Université de Cergy-Pontoise, 5 mail Gay Lussac, F-95000 Cergy-Pontoise, France
³Laboratory Astrophysics Group of the Astrophysical Institute and University Observatory, Friedrich Schiller University Jena Schillergässchen 3, D-07743 Jena, Germany
⁴Max Planck Institute for Astronomy Königstuhl 17, D-69117 Heidelberg, Germany
⁵Physics Department, Syracuse University, Syracuse, NY 13244-1320, USA.

Amorphous, astrophysically relevant silicates were prepared by laser ablation of siliceous targets and subsequent quenching of the evaporated atoms and clusters in a helium/oxygen gas atmosphere. The described gas-phase condensation method can be used to synthesize homogeneous and astrophysically relevant silicates with different compositions ranging from nonstoichiometric magnesium iron silicates to pyroxene- and olivine-type stoichiometry. Analytical tools have been used to characterize the morphology, composition, and spectral properties of the condensates. The nanometer-sized silicate condensates represent a new family of cosmic dust analogs that can generally be used for laboratory studies of cosmic processes related to condensation, processing, and destruction of cosmic dust in different astrophysical environments. The well-characterized silicates comprising amorphous Mg₂SiO₄ and Fe₂SiO₄, as well as the corresponding crystalline silicates forsterite and fayalite, produced by thermal annealing of the amorphous condensates, have been used as real grain surfaces for H₂ formation experiments. A specifically developed ultra-high vacuum apparatus has been used for the investigation of molecule formation experiments. The results of these molecular formation experiments on differently structured Mg₂SiO₄ and Fe₂SiO₄ described in this paper will be the topic of the next paper of this series.

Reference
Sabri T, Gavilan L, Jäger C, Lemaire JL, Vidali G, Mutschke H and Henning T (2014) Interstellar Silicate Analogs for Grain-surface Reaction Experiments: Gas-phase Condensation and Characterization of the Silicate Dust Grains. The Astrophysical Journal Volume 780:180.
[doi:10.1088/0004-637X/780/2/180]

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Myriam Lemelin^1,2,*, Caroline-Emmanuelle Morisset³, Mickaël Germain¹, Victoria Hipkin³, Kalifa Goïta¹ and Paul G. Lucey⁴

¹Département de Géomatique Appliquée, Université de Sherbrooke, Sherbrooke, Québec, Canada
²Now at Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawai‘i at Manoa, Honolulu, Hawaii, USA
³Department of Space Exploration, Canadian Space Agency, Saint-Hubert, Québec, Canada
⁴Hawai‘i Institute of Geophysics and Planetology, Honolulu, Hawaii, USA

We model lunar ilmenite abundances over Mare Australe and Mare Ingenii regions using a new approach; we integrate Lunar Reconnaissance Orbiter Wide Angle Camera (WAC) and Clementine UV-visible/near-infrared (UVVIS/NIR) data to obtain a 14-band mosaic (320-2000 nm). We use Hapke’s radiative transfer equations to compute spectra for various mixtures of orthopyroxene, clinopyroxene, plagioclase, olivine, and ilmenite, with varying grain size, chemistry, and degree of maturity, and find the closest match between the modeled spectra and the spectra of the less mature pixels (optical maturity ≥ 0.2) in the 14-band mosaic. We calculate a “maximum stoichiometrically possible ilmenite content”, using Clementine-derived TiO₂ abundances and the amount of TiO₂ in stoichiometric ilmenite, and use it as a constraint in our model. We validate our methodology with lunar soil spectra of known composition. Our results show that the integrated WAC-UVVIS/NIR data and the UVVIS/NIR data overestimate ilmenite abundances by 8.80 wt % and 7.97 wt %, respectively, when a fixed maximum of 20 wt % ilmenite is used. When the maximum stoichiometrically possible ilmenite content is used as a constraint, the integrated WAC-UVVIS/NIR data give slightly more accurate ilmenite abundance estimation (±2.87 wt %) than when using only UVVIS/NIR data (± 3.04 wt %). We find ilmenite concentrations of 0−11 wt % in Mare Australe and 0−6 wt % in Mare Ingenii region. Ilmenite abundances between 4 and 7 wt % are exposed in Mare Australe, whereas ilmenite abundances between 7 and 11 wt % are found on the walls of 0.6-11.8 km diameter craters within Mare Australe.

Reference
Lemelin M, Morisset C-E, Germain M, Hipkin V, Goïta K and Lucey PG (in press) Ilmenite mapping of the lunar regolith over Mare Australe and Mare Ingenii regions: An optimized multisource approach based on Hapke radiative transfer theory. Journal of Geophysical Research: Planets
[doi:10.1002/2013JE004392]
Published by arrangement with John Wiley & Sons

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Adam J. McKay^a, Nancy J. Chanover^a, Michael A. DiSanti^b, Jeffrey P. Morgenthaler^c, Anita L. Cochran^d, Walter M. Harris^e and Neil Dello Russo^f

^aAstronomy Department, New Mexico State University, 1320 Frenger Mall, Las Cruces, NM 88001 (U.S.A.)
^bGoddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771 (U.S.A.)
^cPlanetary Science Institute, 1700 E. Fort Lowell, Ste 106, Tucson, AZ, 85719 (U.S.A)
^dUniverisity of Texas Austin/McDonald Observatory, 1 University Station, Austin, TX 78712, (U.S.A)
^eDepartment of Applied Science, University of California Davis, 1 Shields Ave., Davis, CA, 95616 (U.S.A)
^fJohns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD, 20723 (U.S.A.)

We present analysis of high spectral resolution optical spectra of comet 103P/Hartley taken during its Fall 2010 apparition. These spectra include transitions belonging to CN, C₂, CH, NH₂, and OI. We measure production rates and mixing ratios from these spectra. We find evidence for large changes in production rates (factors of a few) over the course of a nucleus rotation, in agreement with other measurements. We also measure variability with rotational phase in the CN/H₂O and C₂/CN ratios, which has not been previously reported for any comet. There may also be variability in the NH₂/H₂O ratio with rotational phase, but this trend is not as clear as for CN/H₂O. We interpret the changing mixing ratios as due to H₂O and C₂ being released primarily from the icy grain halo, while the CN parent molecule comes directly from the nucleus. There is evidence that the CH/CN ratio is higher pre-perihelion than post-perihelion. We conclude that the observed CN and NH₂ abundances are consistent with HCN and NH₃ being the dominant parent molecules for these species. The C₂ and CH abundances are higher than those of candidate parent molecules (C₂H₂ and CH₄respectively), so there must be another source for these molecules in 103P’s coma. Carbonaceous dust grains could serve as this source.

Reference
McKay AJ, Chanover NJ, DiSanti MA, Morgenthaler JP, Cochran AL, Harris WM and Russo ND (2013) Rotational Variation of Daughter Species Production Rates in Comet 103P/Hartley: Implications for the Progeny of Daughter Species and the Degree of Chemical Heterogeneity. Icarus 48:2441–2450.
[doi:10.1111/maps.12229]
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And will be back on the 27.12.2013