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

^aApplied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA

During Martian solar days 57–100, the Mars Science Laboratory Curiosity rover acquired and processed a solid (sediment) sample and analyzed its mineralogy and geochemistry with the Chemistry and Mineralogy and Sample Analysis at Mars instruments. An aeolian deposit—herein referred to as the Rocknest sand shadow—was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions. During first-time activities, the Mars Hand Lens Imager (MAHLI) was used to support both science and engineering activities related to sample assessment, collection, and delivery. Here we report on MAHLI activities that directly supported sample analysis and provide MAHLI observations regarding the grain-scale characteristics of the Rocknest sand shadow. MAHLI imaging confirms that the Rocknest sand shadow is one of a family of bimodal aeolian accumulations on Mars—similar to the coarse-grained ripples interrogated by the Mars Exploration Rovers Spirit and Opportunity—in which a surface veneer of coarse-grained sediment stabilizes predominantly fine-grained sediment of the deposit interior. The similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on Mars. We suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation, where winnowing of the fine-sediment fraction results in a relatively low sediment load and a preferential increase in the coarse-grained fraction of the sediment load. The compositional similarity of Martian aeolian deposits supports the potential for global redistribution of fine-grained components, combined with potential local contributions.

Reference
Minitti ME et al. (in press) MAHLI at the Rocknest sand shadow: Science and science-enabling activities. Journal of Geophysical Research – Planets
[doi:10.1002/2013JE004426]
Published by arrangement with John Wiley & Sons

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Howard^a et al. (>10)*
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^aInstitute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA

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

Reference
Howard AW et al. (2013) A rocky composition for an Earth-sized exoplanet. Nature 503:381–384.
[doi:10.1038/nature12767]

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Pepe^a et al. (>>10)*
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^aObservatoire Astronomique de l’Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland

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

Reference
Pepe F et al. (2013) An Earth-sized planet with an Earth-like density. Nature 503:377–380.
[doi:10.1038/nature12768]

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D. Bodewits^a, J.-B. Vincent^b and M.S.P. Kelley^a

^aDepartment of Astronomy, University of Maryland, College Park MD 20742-2421, USA
^bMax-Planck-Institut für Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany

Asteroid (596) Scheila was the first object for which the immediate aftermath of an inter-asteroidal collision was observed. In Dec. 2010, the 113 km-sized asteroid was impacted by a smaller asteroid of less than 100 m in diameter. The scale of the impactor was established by observations of fading ejecta plumes. Comparison of the light curves obtained before and after the impact allowed us to assess how much of Scheila’s surface was altered. Cratering physics based on the impactor size suggests that the size of the affected area is larger than expected, (effective radii of 3.5 – 10 km depending on the change in the albedo of the surface). Similar but more localized albedo changes have been observed on Vesta and the Martian moons, but are not understood. Empirical laws describing ejecta blankets however indicate that at distances between 3.5 – 10 km from the crater, Scheila’s surface would be covered by a thin layer 2 mm to 2 cm thick. This dusting, possibly mixed with bright impactor material may be enough to explain to observed brightness increase. Our results show that sub-critical impacts may play a significant role in processing the surfaces of asteroids. The large effect of small impacts on asteroidal light curves complicate shape modeling.

Reference
Bodewits D, Vincent J-B and Kelley MSP (in press) Scheila’s Scar: Direct Evidence of Impact Surface Alteration on a Primitive Asteroid. Icarus
[doi:10.1016/j.icarus.2013.11.003]
Copyright Elsevier

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