¹Ben Rozitis,¹Eric MacLennan,¹Joshua P. Emery
¹Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, USA

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Reference
Rozitis B, MacLennan E, Emery JP (2014) Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA. Nature 512, 174–176
Link to Article [doi:10.1038/nature13632]

¹Joachim Audouard, ¹François Poulet, ¹Mathieu Vincendon, ¹Jean‐Pierre Bibring, ¹Brigitte Gondet, ¹Yves Langevin, ²Ralph E. Milliken, ³Denis Jouglet

¹Institut d’Astrophysique Spatiale (UPSUD/CNRS), Orsay, France
²Dept. Geological Sciences, Brown University, Providence, RI, U.S.A.
³CNES, Toulouse, France

Here we discuss one of the current reservoirs of water on Mars, the regolith and rocks exposed at the surface. This reservoir is characterized by the presence of H2O- and OH-bearing phases that produce a broad absorption at a wavelength of ~3 µm in near-infrared (NIR) reflectance spectra. This absorption is present in every ice-free spectrum of the Martian surface obtained thus far by orbital NIR spectrometers. We present a quantitative analysis of the global distribution of the 3 µm absorption using the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) imaging spectrometer that has been mapping the surface of Mars at kilometer scale for more than ten years. Based on laboratory reflectance spectra of a wide range of hydrous minerals and phases, we estimate a model-dependent water content of 4 ± 1 wt. % in the equatorial and mid-latitudes. Surface hydration increases with latitude, with an asymmetry in water content between the northern and southern hemispheres. The surface hydration is compared to various parameters (albedo, dust, geological units, time, relative humidity, atmospheric water pressure, and in situ measurements performed by Phoenix and Curiosity) to constrain the nature of the reservoir. We conclude that the nature of the surface hydration of the Martian low latitudes is not adsorbed water but rather more tightly-bound water molecules and hydroxyl groups in the structure of the materials of the near-top surface. A frost-related process best explains the implementation of water into and onto the first microns of the high latitudes Martian regolith.

Reference
Audouard J, Poulet F, Vincendon M, Bibring J-P, Gondet B, Langevin Y, Milliken RE, Jouglet D (2014) Water in the Martian regolith from OMEGA/Mars Express. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004649]

Published by arrangement with John Wiley & Sons

¹D.L.Blaney et al. (>10)*
¹Jet Propulsion Laboratory, Pasadena, California Institute of Technology, CA, USA
*Find the extensive, full author and affiliation list on the publishers Website

A suite of eight rocks analyzed by the Curiosity Rover while it was stopped at the Rocknest sand ripple show the greatest chemical divergence of any potentially sedimentary rocks analyzed in the early part of the mission. Relative to average martian soil and to the stratigraphically lower units encountered as part of the Yellowknife Bay formation, these rocks are significantly depleted in MgO, with a mean of 1.3 wt %, and high in Fe, averaging over 20 wt % FeOT. with values between 15 – 26 wt% FeOT. The variable iron and low magnesium, and rock texture make it unlikely that these are igneous rocks. Rock surface textures range from rough to smooth, can be pitted or grooved, and show various degrees of wind erosion. Some rocks display poorly defined layering while others seem to show possible fractures. Narrow vertical voids are present in Rocknest-3, one of the rocks showing the strongest layering. Rocks in the vicinity of Rocknest may have undergone some diagenesis similar to other rocks in the Yellowknife Bay Formation as indicated by the presence of soluble calcium phases. The most reasonable scenario is that fine-grained sediments, potentially a mixture of feldspar-rich rocks from Bradbury Rise and normal martian soil, was lithified together by an iron-rich cement.

Reference
Blaney DL et al. (2014) Chemistry and texture of the rocks at Rocknest, Gale Crater: Evidence for sedimentary origin and diagenetic Alteration. Journal of Geophysical Research Planets (in Press)
Link to Article [doi: 10.1002/2013JE004590]

Published by arrangement with John Wiley & Sons

^1,2Ian A. Crawford, ³Katherine H. Joy
¹Department of Earth and Planetary Sciences, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK
²Centre for Planetary Sciences at UCL/Birkbeck, Gower Street, London WC1E 6BT, UK
³School of Earth, Atmospheric and Environmental Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK

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Reference
Crawford IA, Joy KH (2014) Lunar exploration: opening a window into the history and evolution of the inner Solar System. Philosophical Transactions of the Royal Society A13, 372, 2024
Link to Article [doi:10.1098/rsta.2013.0315]

¹Linda T. Elkins-Tanton ²David Bercovici
¹Department of Terrestrial Magnetism, Carnegie Institution for Science, Washington DC, USA
²Department of Geology and Geophysics, Yale University, New Haven, CT, USA

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Reference
Elkins-Tanton LT, Bercovici D (2014) Contraction or expansion of the Moon’s crust during magma ocean freezing? Philosophical Transactions of the Royal Society A 13, 372, 2024
Link to Article [doi: 10.1098/rsta.2013.0240]