A. P. Jones^1,2, L. Fanciullo^1,2, M. Köhler^1,2, L. Verstraete^1,2, V. Guillet^1,2, M. Bocchio^1,2 and N. Ysard^1,2

¹CNRS, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France
²Université Paris Sud, Institut d’Astrophysique Spatiale, UMR 8617, 91405 Orsay, France

Context. The evolution of amorphous hydrocarbon materials, a-C(:H), principally resulting from ultraviolet (UV) photon absorption-induced processing, are likely at the heart of the variations in the observed properties of dust in the interstellar medium.
Aims. The consequences of the size-dependent and compositional variations in a-C(:H), from aliphatic-rich a-C:H to aromatic-rich a-C, are studied within the context of the interstellar dust extinction and emission.
Methods. Newly-derived optical property data for a-C(:H) materials, combined with that for an amorphous forsterite-type silicate with iron nano-particle inclusions, a-Sil_Fe, are used to explore dust evolution in the interstellar medium.
Results. We present a new dust model that consists of a power-law distribution of small a-C grains and log-normal distributions of large a-Sil_Fe and a-C(:H) grains. The model, which is firmly anchored by laboratory-data, is shown to quite naturally explain the variations in the infrared (IR) to far-ultraviolet (FUV) extinction, the 217 nm UV bump, the IR absorption and emission bands and the IR-mm dust emission.
Conclusions. The major strengths of the new model are its inherent simplicity and built-in capacity to follow dust evolution in interstellar media. We show that mantle accretion in molecular clouds and UV photo-processing in photo-dominated regions are likely the major drivers of dust evolution.

Reference
Jones AP, Fanciullo L, Köhler M, Verstraete L, Guillet V, Bocchio M and Ysard N (in press) The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point. Astronomy & Astrophysics
[doi:10.1051/0004-6361/201321686]
Reproduced with permission © ESO

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Tomas Kohout^a,b,*, Maria Gritsevich^c,d,e, Victor I. Grokhovsky^f, Grigoriy A. Yakovlev^f, Jakub Haloda^g,h, Patricie Halodova^g, Radoslaw M. Michallikⁱ, Antti Penttilä^a, Karri Muinonen^a,c

^aDepartment of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki University, Finland
^bInstitute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 269, 16500 Prague 6, Czech Republic
^cFinnish Geodetic Institute, Geodeetinrinne 2, P.O. Box 15, FI-02431 Masala, Finland
^dInstitute of Mechanics, Lomonosov Moscow State University, Michurinsky prt., 1, 119192, Moscow, Russia
^eRussian Academy of Sciences, Dorodnicyn Computing Centre, Department of Computational Physics, Vavilova ul. 40, 119333 Moscow, Russia
^fUral Federal University, Ekaterinburg, Russia
^gCzech Geological Survey, Geologická 6, 152 00 Praha 5, Czech Republic
^hOxford Instruments NanoAnalysis, Halifax Road, High Wycombe, Bucks, HP12 3SE, United Kingdom
ⁱDepartment of Geosciences and Geography, University of Helsinki, P.O. Box 64, 00014 Helsinki University, Finland

The mineralogy and physical properties of Chelyabinsk meteorites (fall, February 15, 2013) are presented. Three types of meteorite material are present, described as the light-colored, dark-colored, and impact-melt lithologies. All are of LL5 composition with the impact-melt lithology being close to whole-rock melt and the dark-colored lithology being shock-darkened due to partial melting of iron metal and sulfides. This enables us to study the effect of increasing shock on material with identical composition and origin. Based on the magnetic susceptibility, the Chelyabinsk meteorites are richer in metallic iron as compared to other LL chondrites. The measured bulk and grain densities and the porosity closely resemble other LL chondrites. Shock-darkening does not have a significant effect on the material physical properties, but causes a decrease of reflectance and decrease in silicate absorption bands in the reflectance spectra. This is similar to the space weathering effects observed on asteroids. However, compared to space weathered materials, there is a negligible to minor slope change observed in impact-melt and shock-darkened meteorite spectra. Thus, it is possible that some dark asteroids with invisible silicate absorption bands may be composed of relatively fresh shock-darkened chondritic material.

Reference
Kohout T, Gritsevich M, Grokhovsky VI, Yakovlev GA, Haloda J, Halodova P, Michallik RM, Penttilä A and Muinonen K (in press) Mineralogy, reflectance spectra, and physical properties of the Chelyabinsk LL5 chondrite – insight into shock-induced changes in asteroid regoliths. Icarus
[doi:10.1016/j.icarus.2013.09.027]
Copyright Elsevier

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P. D. Spudis^1,*, D. B. J. Bussey², S. M. Baloga³, J. T. S. Cahill², L. S. Glaze⁴, G. W. Patterson², R. K. Raney², T. W. Thompson⁵, B. J. Thomson⁶, E. A. Ustinov⁵

¹Lunar and Planetary Institute, Houston, Texas, USA
²Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
³Proxemy Research, Laytonsville, Maryland, USA
⁴NASA Goddard Spaceflight Center, Greenbelt, Maryland, USA
⁵Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
⁶Center for Remote Sensing, Boston University, Boston, Massachusetts, USA

The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth- and spacecraft-based radar mapping of the Moon’s polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively “clean” ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

Reference
Spudis PD, Bussey DBJ, Baloga SM. Cahill JTS, Glaze LS, Patterson GW, Raney RK, Thompson TW, Thomson BJ and Ustinov EA (in press) Evidence for water ice on the moon: Results for anomalous polar craters from the LRO Mini-RF imaging radar. Journal of Geophysical Research – Planets, 118
[doi:10.1002/jgre.20156]
Published by arrangement with John Wiley & Sons

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