¹James M.T. Lewis, ¹Jonathan S. Watson, ²Jens Najorka, ¹Duy Luong, ¹Mark A. Sephton
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, United Kingdom.
²Impacts and Astromaterials Research Centre, Department of Mineralogy, Natural History Museum, London, United Kingdom.

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

Reference
Lewis JMT, Watson JS, Najorka J, Luong D, Sephton MA (2015) Sulfate Minerals: A Problem for the Detection of Organic Compounds on Mars? Astrobiology 15(3): 247-258
Link to Article [doi:10.1089/ast.2014.1160]

¹Charles A. Poteet, ¹Douglas C. B. Whittet, ²Bruce T. Draine
¹New York Center for Astrobiology, Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, NY 12180, USA
²Princeton University Observatory, Peyton Hall, Princeton, NJ 08544, USA

We investigate the composition of interstellar grains along the line of sight toward ζ Ophiuchi, a well-studied environment near the diffuse-dense cloud transition. A spectral decomposition analysis of the solid-state absorbers is performed using archival spectroscopic observations from the Spitzer Space Telescope and Infrared Space Observatory. We find strong evidence for the presence of sub-micron-sized amorphous silicate grains, principally comprised of olivine-like composition, with no convincing evidence of H2O ice mantles. However, tentative evidence for thick H2O ice mantles on large (a ≈ 2.8 μm) grains is presented. Solid-state abundances of elemental Mg, Si, Fe, and O are inferred from our analysis and compared to standard reference abundances. We find that nearly all of the Mg and Si atoms along the line of sight reside in amorphous silicate grains, while a substantial fraction of the elemental Fe resides in compounds other than silicates. Moreover, we find that the total abundance of elemental O is largely inconsistent with the adopted reference abundances, indicating that as much as ~156 ppm of interstellar O is missing along the line of sight. After taking into account additional limits on the abundance of elemental O in other O-bearing solids, we conclude that any missing reservoir of elemental O must reside on large grains that are nearly opaque to infrared radiation.

Reference
Poteet PA, Whittet DCB, Draine BT (2015) The Composition of Interstellar Grains toward ζ Ophiuchi: Constraining the Elemental Budget near the Diffuse-dense Cloud Transition. Astrophysical Journal 801, 110.
Link to Article [doi:10.1088/0004-637X/801/2/110]

¹Nicole G. Lunning,¹Harry Y. McSween Jr.,²Travis J. Tenner,³Noriko T. Kita,⁴Robert J. Bodnar
¹Department of Earth and Planetary Sciences and Planetary Geosciences Institute, University of Tennessee, Knoxville, TN 37996, USA
²Department of Geosciences, University of Wisconsin, Madison, WI 53706, USA
³Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA

A number of meteorites contain evidence that rocky bodies formed and differentiated early in our solar system’s history, and similar bodies likely contributed material to form the planets. These differentiated rocky bodies are expected to have mantles dominated by Mg-rich olivine, but direct evidence for such mantles beyond our own planet has been elusive. Here, we identify olivine fragments (Mg# = 80–92) in howardite meteorites. These Mg-rich olivine fragments do not correspond to an established lithology in the howardite–eucrite–diogenite (HED) meteorites, which are thought to be from the asteroid 4 Vesta; their occurrence in howardite breccias, combined with diagnostic oxygen three-isotope signatures and minor element chemistry, indicates they are vestan. The major element chemistry of these Mg-rich olivines suggests that they formed as mantle residues, in crustal layered intrusions, or in Mg-rich basalts. The trace element chemistry of these Mg-rich olivines supports an origin as mantle samples, but other formation scenarios could be possible. Interpreted as mantle samples, the range of Mg-rich olivine compositions indicates that Vesta’s structure differs from that predicted by conventional models: Vesta has a chemically heterogeneous mantle that feeds serial magmatism. The range of olivine major element chemistries is consistent with models of an incompletely melted mantle such as in the model proposed by Wilson and Keil (2013) rather than a whole-mantle magma ocean for Vesta. Trace element chemistries of Mg-rich pyroxenes (Mg# = 85–92) provide support that some of these pyroxenes may represent initial fractional crystallization of mantle partial melts.

Reference
Lunning NG,McSween Jr. HY,Tenner TJ, Kita NT, Bodnar RJ (2015) Olivine and pyroxene from the mantle of asteroid 4 Vesta. Earth and Planetary Science Letters 418, 126–135
Link to Article [doi:10.1016/j.epsl.2015.02.043]

Copyright Elsevier

^1,2Haolan Tang, ¹Nicolas Dauphas
¹Origins Lab, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA
²Ion Probe Group, Department of earth and Space Sciences, University of California, Los Angeles, 595 Charles E. Young Drive East, Los Angeles, CA 90095, US

Iron-60 (t1/2 = 2.62 Myr) is a short-lived nuclide that can help constrain the astrophysical context of Solar System formation and date early Solar System events. A high abundance of 60Fe(60Fe/56Fe ≈ 4 × 10−7) was reported by in situ techniques in some chondrules from the LL3.00 Semarkona meteorite, which was taken as evidence that a supernova exploded in the vicinity of the birthplace of the Sun. However, our previous multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) measurements of a wide range of meteoritic materials, including chondrules, showed that 60Fe was present in the early Solar System at a much lower level (60Fe/56Fe ≈ 10−8). The reason for the discrepancy is unknown but only two Semarkona chondrules were measured by MC-ICPMS and these had Fe/Ni ratios below ~2× chondritic. Here, we show that the initial 60Fe/56Fe ratio in Semarkona chondrules with Fe/Ni ratios up to ~24× chondritic is (5.39 ± 3.27) × 10−9. We also establish the initial 60Fe/56Fe ratio at the time of crystallization of the Sahara 99555 angrite, a chronological anchor, to be (1.97 ± 0.77) × 10−9. These results demonstrate that the initial abundance of 60Fe at Solar System birth was low, corresponding to an initial 60Fe/56Fe ratio of (1.01 ± 0.27) × 10−8.

Reference
Tang H, Dauphas N (2015) Low 60Fe Abundance in Semarkona and Sahara 99555. Astrophysical Journal 802 22.
Link to Article [doi:10.1088/0004-637X/802/1/22]