Johnson et al.^a et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

^aJohns Hopkins University Applied Physics Laboratory, Laurel, MD

The spectrometers on the Mars Science Laboratory (MSL) ChemCam instrument were used in passive mode to record visible/near-infrared (400-840 nm) radiance from the martian surface. Using the onboard ChemCam calibration targets’ housing as a reflectance standard, we developed methods to collect, calibrate, and reduce radiance observations to relative reflectance. Such measurements accurately reproduce the known reflectance spectra of other calibration targets on the rover, and represent the highest spatial resolution (0.65 mrad) and spectral sampling (< 1 nm) visible/near-infrared reflectance spectra from a landed platform on Mars. Relative reflectance spectra of surface rocks and soils match those from orbital observations and multispectral data from the MSL Mastcam camera. Preliminary analyses of the band depths, spectral slopes, and reflectance ratios of the more than 2,000 spectra taken during the first year of MSL operations demonstrate at least six spectral classes of materials distinguished by variations in ferrous and ferric components. Initial comparisons of ChemCam spectra to laboratory spectra of minerals and Mars analog materials demonstrate similarities with palagonitic soils and indications of orthopyroxene in some dark rocks. Magnesium-rich “raised ridges” tend to exhibit distinct near-infrared slopes. The ferric absorption downturn typically found for martian materials at < 600 nm is greatly subdued in brushed rocks and drill tailings, consistent with their more ferrous nature. Calcium-sulfate veins exhibit the highest relative reflectances observed, but are still relatively red owing to the effects of residual dust. Such dust is overall less prominent on rocks sampled within the “blast zone” immediately surrounding the landing site. These samples were likely affected by the landing thrusters, which partially removed the ubiquitous dust coatings. Increased dust coatings on the calibration targets during the first year of the mission were documented by the ChemCam passive measurements as well. Ongoing efforts to model and correct for this dust component should improve calibration of the relative reflectance spectra. This will be useful as additional measurements are acquired during the rover’s future examinations of hematite-, sulfate-, and phyllosilicate-bearing materials near the base of Mt. Sharp that are spectrally active in the 400-840 nm region.

Reference
Johnson et al. (in press) ChemCam Passive Reflectance Spectroscopy of Surface Materials at the Curiosity Landing Site, Mars. Icarus
[doi:10.1016/j.icarus.2014.02.028]
Copyright Elsevier

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Martin Beech

Campion College, The University of Regina, Regina, SK, S4S 0A2, Canada

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

Reference
Beech M (2013) Towards an Understanding of the Fall Circumstances of the Hoba Meteorite. Earth, Moon, and Planets 111:15-30.
[doi:10.1007/s11038-013-9421-7]

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G. Duchêne^1,15 et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Astronomy Department, University of California, Berkeley, CA 94720, USA
¹⁵UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique (IPAG) UMR 5274, F-38041 Grenoble, France.

We present far-infrared and submillimeter images of the η Crv debris disk system obtained with Herschel and SCUBA-2, as well asHubble Space Telescope visible and near-infrared coronagraphic images. In the 70 μm Herschel image, we clearly separate the thermal emission from the warm and cold belts in the system, find no evidence for a putative dust population located between them, and precisely determine the geometry of the outer belt. We also find marginal evidence for azimuthal asymmetries and a global offset of the outer debris ring relative to the central star. Finally, we place stringent upper limits on the scattered light surface brightness of the outer ring. Using radiative transfer modeling, we find that it is impossible to account for all observed properties of the system under the assumption that both rings contain dust populations with the same properties. While the outer belt is in reasonable agreement with the expectations of steady-state collisional cascade models, albeit with a minimum grain size that is four times larger than the blow-out size, the inner belt appears to contain copious amounts of small dust grains, possibly below the blow-out size. This suggests that the inner belt cannot result from a simple transport of grains from the outer belt and rather supports a more violent phenomenon as its origin. We also find that the emission from the inner belt has not declined over three decades, a much longer timescale than its dynamical timescale, which indicates that the belt is efficiently replenished.

Reference
Duchêne et al. (2014) Spatially Resolved Imaging of the Two-component η Crv Debris Disk with Herschel G. The Astrophysical Journal 784:148.
[doi:10.1088/0004-637X/784/2/148]

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N. Patra^1,3, P. Král^1,2 and H. R. Sadeghpour³

¹Department of Chemistry, University of Illinois at Chicago, Chicago, IL 60607, USA
²Department of Physics, University of Illinois at Chicago, Chicago, IL 60607, USA
³ITAMP, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA

We study the conditions under which carbon clusters of different sizes form and stabilize. We describe the approach to equilibrium by simulating tenuous carbon gas dynamics to long times. First, we use reactive molecular dynamics simulations to describe the nucleation of long chains, large clusters, and complex cage structures in carbon- and hydrogen-rich interstellar gas phases. We study how temperature, particle density, the presence of hydrogen, and carbon inflow affect the nucleation of molecular moieties with different characteristics, in accordance with astrophysical conditions. We extend the simulations to densities that are orders of magnitude lower than current laboratory densities, to temperatures that are relevant to circumstellar environments of planetary nebulae, and microsecond formation times. We correlate cluster size distributions from the simulations with thermodynamic equilibrium at low temperatures and gas densities, where entropy plays a significant role.

Reference
Patra N, Král P and Sadeghpour HR (2014) Nucleation and Stabilization of Carbon-rich Structures in Interstellar Media. The Astrophysical Journal 785:6.
[doi:10.1088/0004-637X/785/1/6]

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