C. T. Adcock¹, E. M. Hausrath¹ and P. M. Forster²

¹Department of Geoscience, University of Nevada Las Vegas, 4505 S. Maryland Pkwy., Las Vegas, Nevada 89154, USA
²Department of Chemistry, University of Nevada Las Vegas, 4505 S. Maryland Pkwy., Las Vegas, Nevada 89154, USA

We currently seek a copyright agreement with Nature Geoscience to display abstracts of their cosmochemistry related publications.

Reference
Adcock CT, Hausrath EM and Forster PM  (2013) Readily available phosphate from minerals in early aqueous environments on Mars. Nature Geoscience 6:824–827.
[doi:10.1038/ngeo1923]

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Arkaprabha Sarangi and Isabelle Cherchneff

We study the formation of molecules and dust clusters in the ejecta of solar metallicity, Type II-P supernovae (SNe) using a chemical kinetic approach. We follow the evolution of molecules and small dust cluster masses from day 100 to day 1500 after explosion. We consider stellar progenitors with initial masses of 12, 15, 19, and 25 M_☉ that explode as SNe with stratified ejecta. The molecular precursors to dust grains comprise molecular chains, rings and small clusters of silica, silicates, metal oxides, sulfides and carbides, pure metals, and carbon, where the nucleation of silicate clusters is described by a two-step process of metal and oxygen addition. We study the impact of the ⁵⁶Ni mass on the type and amount of synthesized dust. We predict that large masses of molecules including CO, SiO, SiS, O₂, and SO form in the ejecta. We show that the discrepancy between the small dust masses detected at infrared wavelengths some 500 days post-explosion and the larger amounts of dust recently detected with Herschel in SN remnants can be explained by the non-equilibrium chemistry linked to the formation of molecules and dust clusters in the ejected material. Dust gradually builds up from small (~10−5 M_☉) to large masses (~5 × 10−2 M_☉) over a 5 yr period after explosion. Subsequent dust formation and/or growth is hampered by the shortage of chemical agents participating in the dust nucleation and the long timescale for accretion. The results highlight the dependence of the dust chemical composition and mass on the amount of ⁵⁶Ni synthesized during the explosion. This dependence may partly explain the diversity of epochs at which dust forms in SNe. More generally, our results indicate that Type II-P SNe are efficient but moderate dust producers with an upper limit on the mass of synthesized dust ranging from ~0.03 to 0.09 M_☉. Other dust sources must then operate at high redshift to explain the large quantities of dust present in young galaxies in the early universe.

Reference
Sarangi A and Cherchneff I (in press) The Chemically Controlled Synthesis of Dust in Type II-P Supernovae. The Astrophysical Journal
[doi:10.1088/0004-637X/776/2/107]

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A. Pommerol^1,*, N. Thomas¹, B. Jost¹, P. Beck², C. Okubo³, A. S. McEwen⁴

¹Physikalisches Institut, Universität Bern, Bern, Switzerland
²Institut de Planétologie et d’Astrophysique de Grenoble, UMR 5274, CNRS/Université Grenoble I, Grenoble, France
³U.S. Geological Survey, Astrogeology Research Center Survey, Flagstaff, Arizona, USA
⁴Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA

We have measured the bidirectional reflectance of analogs of dry, wet, and frozen Martian soils over a wide range of phase angles in the visible spectral range. All samples were produced from two geologic samples: the standard JSC Mars-1 soil simulant and Hawaiian basaltic sand. In a first step, experiments were conducted with the dry samples to investigate the effects of surface texture. Comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures. In a second step, water was introduced to produce wet and frozen samples and their photometry investigated. Optical microscope images of the samples provided information about their microtexture. Liquid water, even in relatively low amount, resulted in the disappearance of the backscattering peak and the appearance of a forward-scattering peak whose intensity increases with the amount of water. Specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample. Icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice. We discuss the implications of these measurements in terms of the expected photometric behavior of the Martian surface, from equatorial to circum-polar regions. In particular, we propose some simple photometric criteria to improve the identification of wet and/or icy soils from multiple observations under different geometries.

Reference
Pommerol A, Thomas N, Jost B, Beck P, Okubo C and McEwen AS (in press) Photometric properties of Mars soils analogs. Journal of Geophysical Research – Planets, 118
[doi:10.1002/jgre.20158]
Published by arrangement with John Wiley & Sons

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