^1,2C. Freissinet et al. (>10)*
¹Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD, USA
²NASA Postdoctoral Program, (NPP), Oak Ridge Associated Universities, Oak Ridge, Tennessee, USA
*Find the extensive, full author and affiliation list on the publishers website

The Sample Analysis at Mars (SAM) instrument [Mahaffy et al., 2012] onboard the Mars Science Laboratory (MSL) Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater [Grotzinger et al., 2012]. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration and long-term preservation. This will guide the future search for biosignatures [Summons et al., 2011]. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS), and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources (e.g. igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets or interplanetary dust particles.

Reference
Freissinet C et al. (2015) Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars. Journal of Geophysical Research, Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004737]

Published by arrangement with John Wiley&Sons

¹Abu Asaduzzaman,¹Krishna Muralidharan,²Jibamitra Ganguly
¹Materials Science and Engineering, University of Arizona, Tucson, Arizona, USA
²Department of Geoscience, University of Arizona, Tucson, 85721, USA

Using density functional theory, we have examined the hydration mechanism of olivine with the objective of understanding the reaction pathways toward the formation of crystalline serpentine and brucite. It is found that further supply of water beyond saturation of the adsorption sites on olivine surfaces leads to the formation of amorphous brucite and serpentine molecules, with the latter forming in the subsurface domain. The calculated activation energy for this process is ~25 kJ mol−1, which permits formation of the amorphous materials well within the life span of the solar nebula. In addition, molecular dynamic simulations show that the adsorbed water in olivine is stable at least up to 900 K—a finding that is in accord with independent experimental studies. Thus, adsorption plus subsurface reaction of H2O in olivine could have taken place at temperatures considerably higher than the stability limit of hydrous minerals in the nebular condition. Using the DFT derived enthalpy of adsorption data, and reasonable approximation for the entropy of adsorption, we have calculated the fractional coverage of the reactive surface sites of olivine grains of spherical geometry by adsorbed water, and the corresponding ocean equivalent water (OEW) that could have been accreted into the Earth. These results suggest that adsorption and the associated subsurface hydroxylation of olivine grains might have been responsible for a significant fraction of the Earth’s water budget. The adsorption of water into olivine crystals in the solar nebula might also have led to the delivery of water to other planetary bodies.

Reference
Asaduzzaman A, Muralidharan K, Ganguly J (2015) Incorporation of water into olivine during nebular condensation: Insights from density functional theory and thermodynamics, and implications for phyllosilicate formation and terrestrial water inventory. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12409]

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