Joshua F. Snape^1,2,3, Katherine H. Joy^2,4, Ian A. Crawford^2,5 and Louise Alexander^2,5

¹Department of Physical Sciences, Open University, Milton Keynes, UK
²The Centre for Planetary Sciences at UCL-Birkbeck, London, UK
³Department of Earth Sciences, University College London, London, UK
⁴School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK
⁵Department of Earth and Planetary Sciences, Birkbeck College, University of London, London, UK

A detailed petrologic survey has been made of 17 basaltic chips (sized between 1 and 10 mm) from the 12003 soil sample as part of an ongoing study of basaltic diversity at the Apollo 12 landing site. An attempt has been made to classify these samples according to the well-established grouping of olivine, pigeonite, ilmenite, and feldspathic basalts. Particular attention has been paid to variations in major, minor, and trace element mineral chemistry (determined by electron microprobe analysis and laser ablation ICP-MS), which may be indicative of particular basaltic suites and less susceptible to sampling bias than bulk sample characteristics. Examples of all three main (olivine, pigeonite, and ilmenite) basaltic suites have been identified within the 12003 soil. One sample is identified as a possible new addition to the feldspathic suite, which currently consists of only one other confirmed sample. Identification of additional feldspathic basalts strengthens the argument that they represent a poorly sampled basaltic flow local to the Apollo 12 site, rather than exotic material introduced to the site by impact mixing processes. Three samples are identified as representing members of one or two previously unrecognized basaltic suites.

Reference
Snape JF, Joy KH, Crawford IA and Alexander L (in press) Basaltic diversity at the Apollo 12 landing site: Inferences from petrologic examinations of the soil sample 12003. Meteoritics & Planetary Science
[doi:10.1111/maps.12285]
Published by arrangement with John Wiley & Sons

Link to Article

Stanley G. Love¹, Donald R. Pettit¹ and Scott R. Messenger²

¹NASA Lyndon B. Johnson Space Center, Houston, Texas, USA
²Robert M. Walker Laboratory for Space Science, Astromaterials Research and Exploration Science Directorate, NASA Lyndon B. Johnson Space Center, Houston, Texas, USA

We conducted experiments in space to investigate the aggregation of millimeter- and submillimeter-sized particles in microgravity, an important early step in planet formation. Particulate materials included salt (NaCl), sugar (sucrose), coffee, mica, ice, Bjurböle chondrules, ordinary and carbonaceous chondrite meteorite fragments, and acrylic and glass beads, all triply confined in clear plastic containers. Angular submillimeter particles rapidly and spontaneously formed clusters strong enough to survive turbulence in a protoplanetary nebula. Smaller particles generally aggregated more strongly and quickly than larger ones. We observed only a weak dependence of aggregation time on particle number density. We observed no strong dependence on composition. Round, smooth particles aggregated weakly or not at all. In a mixture of particle types, some phases aggregated more readily than others, creating selection effects that controlled the composition of the growing clumps. The physical process of aggregation appears to be electrostatic in nature.

Reference
Love SG, Pettit DR and Messenger SR (in press) Particle aggregation in microgravity: Informal experiments on the International Space Station. Meteoritics & Planetary Science
[doi:10.1111/maps.12286]
Published by arrangement with John Wiley & Sons

Link to Article

Monique C. Aller¹, Varsha P. Kulkarni¹, Donald G. York², Daniel E. Welty², Giovanni Vladilo³ and Nicholas Liger¹

¹Department of Physics and Astronomy, University of South Carolina, 712 Main Street, Columbia, SC 29208, USA
²Department of Astronomy & Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
³Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34143 Trieste, Italy

We report the detection of interstellar silicate dust in the z_abs = 0.685 absorber along the sightline toward the gravitationally lensed blazar TXS 0218+357. Using Spitzer Space Telescope Infrared Spectrograph data, we detect the 10 μm silicate absorption feature with a detection significance of 10.7σ. We fit laboratory-derived silicate dust profile templates obtained from the literature to the observed 10 μm absorption feature and find that the best single-mineral fit is obtained using an amorphous olivine template with a measured peak optical depth of τ₁₀ = 0.49 ± 0.02, which rises to τ₁₀ ~ 0.67 ± 0.04 if the covering factor is taken into account. We also detected the 18 μm silicate absorption feature in our data with a >3σ significance. Due to the proximity of the 18 μm absorption feature to the edge of our covered spectral range, and associated uncertainty about the shape of the quasar continuum normalization near 18 μm, we do not independently fit this feature. We find, however, that the shape and depth of the 18 μm silicate absorption are well matched to the amorphous olivine template prediction, given the optical depth inferred for the 10 μm feature. The measured 10 μm peak optical depth in this absorber is significantly higher than those found in previously studied quasar absorption systems. However, the reddening, 21 cm absorption, and velocity spread of Mg II are not outliers relative to other studied absorption systems. This high optical depth may be evidence for variations in dust grain properties in the interstellar medium between this and the previously studied high redshift galaxies.

Reference
Aller MC, Kulkarni VP, York DG, Welty DE, Vladilo G and Liger N (2014) Interstellar Silicate Dust in the z = 0.685 Absorber Toward TXS 0218+357. The Astrophysical Journal 785:36.
[doi:10.1088/0004-637X/785/1/36]

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