Karen E. Smith^A, Michael P. Callahan^b, Perry A. Gerakines^b, Jason P. Dworkin^b, Christopher H. House^a

^aDepartment of Geosciences and Penn State Astrobiology Research Center, Pennsylvania State University, 220 Deike Building, University Park, PA 16802, USA
^bSolar System Exploration Division and the Goddard Center for Astrobiology, National Aeronautics and Space Administration Goddard Space Flight Center, Gr

The distribution and abundances of pyridine carboxylic acids (including nicotinic acid) in eight CM2 carbonaceous chondrites (ALH 85013, DOM 03183, DOM 08003, EET 96016, LAP 02333, LAP 02336, LEW 85311, and WIS 91600) were investigated by liquid chromatography coupled to UV detection and high resolution Orbitrap mass spectrometry. We find that pyridine monocarboxylic acids are prevalent in CM2-type chondrites and their abundance negatively correlates with the degree of pre-terrestrial aqueous alteration that the meteorite parent body experienced. We also report the first detection of pyridine dicarboxylic acids in carbonaceous chondrites. Additionally, we carried out laboratory studies of proton-irradiated pyridine in carbon dioxide-rich ices (a 1:1 mixture) to serve as a model of the interstellar ice chemistry that may have led to the synthesis of pyridine carboxylic acids. Analysis of the irradiated ice residue shows that a comparable suite of pyridine mono- and dicarboxylic acids was produced, although aqueous alteration may still play a role in the synthesis (and ultimate yield) of these compounds in carbonaceous meteorites. Nicotinic acid is a precursor to nicotinamide adenine dinucleotide, a likely ancient molecule used in cellular metabolism in all of life, and its common occurrence in CM2 chondrites may indicate that meteorites may have been a source of molecules for the emergence of more complex coenzymes on the early Earth.

Reference
Smith KE, Callahan MP, Gerakines PA, Dworkin JP and House CH (in press) Investigation of Pyridine Carboxylic Acids in CM2 Carbonaceous Chondrites: Potential Precursor Molecules for Ancient Coenzymes. Geochimica et Cosmochimica Acta
[doi:10.1016/j.gca.2014.04.001]
Copyright Elsevier

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J. Steinacker^1,2, C. W. Ormel³, M. Andersen¹ and A. Bacmann¹

¹UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
²Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³Astronomy Department, University of California, Berkeley, CA 94720, USA

Context. With the initial steps of the star formation process in the densest part of the interstellar medium (ISM) still under debate, much attention is paid to the formation and evolution of pre-stellar cores. The recently discovered coreshine effect can aid in exploring the core properties and in probing the large grain population of the ISM.
Aims. We discuss the implications of the coreshine detected from the molecular cloud core L1506C in the Taurus filament for the history of the core and the existence of a primitive ISM component of large grains becoming visible in cores.
Methods. The coreshine surface brightness of L1506C is determined from Spitzer IRAC images at 3.6 μm. We perform grain growth calculations to estimate the grain size distribution in model cores similar in gas density, radius, and turbulent velocity to L1506C. Scattered light intensities at 3.6 μm are calculated for a variety of MRN and grain growth distributions using the DIRBE 3.5 μm all-sky map as external interstellar radiation field, and are compared to the observed coreshine surface brightness.}
Results. For a core with the overall physical properties of L1506C, no detectable coreshine is predicted with a size distribution following the shape and size limits of an MRN distribution. Extending the distribution to grain radii of about 0.65 μm allows to reproduce the observed surface brightness level in scattered light. Assuming the properties of L1506C to be preserved, models for the growth of grains in cores do not yield sufficient scattered light to account for the coreshine within the lifetime of the Taurus complex. Only increasing the core density and the turbulence amplifies the scattered light intensity to a level consistent with the observed coreshine brightness.
Conclusions. The coreshine observed from L1506C requires the presence of grains with sizes exceeding the common MRN distribution. The grains could be part of primitive omni-present large grain population becoming visible in the densest part of the ISM, could grow under the turbulent dense conditions of former cores, or in L1506C itself. In the later case, L1506C must have passed through a period of larger density and stronger turbulence. This would be consistent with the surprisingly strong depletion usually attributed to high column densities, and with the large-scale outward motion of the core envelope observed today.

Reference
Steinacker J, Ormel CW, Andersen M and Bacmann A (2014) Coreshine in L1506C – Evidence for a primitive big-grain component or indication for a turbulent core history? Astronomy & Astrophysics 564:A96.
[doi:10.1051/0004-6361/201322117]
Reproduced with permission © ESO

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