P. J. Wozniakiewicz^1,2, J. P. Bradley³, H. A. Ishii³, M. C. Price² and D. E. Brownlee⁴

¹Earth Sciences Department, Mineral and Planetary Science Division, Natural History Museum, Cromwell Road, London SW7 5BD, UK
²School of Physical Sciences, University of Kent, Canterbury, Kent CT2 7NH, UK
³Institute of Geophysics and Planetary Physics, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
⁴Department of Astronomy, University of Washington, Seattle, WA 98195, USA

Despite their micrometer-scale dimensions and nanogram masses, chondritic porous interplanetary dust particles (CP IDPs) are an important class of extraterrestrial material since their properties are consistent with a cometary origin and they show no evidence of significant post-accretional parent body alteration. Consequently, they can provide information about grain accretion in the comet-forming region of the outer solar nebula. We have previously reported our comparative study of the sizes and size distributions of crystalline silicate and sulfide grains in CP IDPs, in which we found these components exhibit a size–density relationship consistent with having been sorted together prior to accretion. Here we extend our data set and include GEMS (glass with embedded metal and sulfide), the most abundant amorphous silicate phase observed in CP IDPs. We find that while the silicate and sulfide sorting trend previously observed is maintained, the GEMS size data do not exhibit any clear relationship to these crystalline components. Therefore, GEMS do not appear to have been sorted with the silicate and sulfide crystals. The disparate sorting trends observed in GEMS and the crystalline grains in CP IDPs present an interesting challenge for modeling early transport and accretion processes. They may indicate that several sorting mechanisms operated on these CP IDP components, or alternatively, they may simply be a reflection of different source environments.

Reference
Wozniakiewicz PJ, Bradley JP, Ishii HA, Price MC and Brownlee DE (2013) Pre-Accretional Sorting of Grains in the Outer Solar Nebula. The Astrophysical Journal 779:164.
[doi:10.1088/0004-637X/779/2/164]

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Dana E. Anderson¹, Edwin A. Bergin¹, Sébastien Maret² and Valentine Wakelam^3,4

¹Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1042, USA
²UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, F-38041, France
³Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac, France
⁴CNRS, LAB, UMR 5804, F-33270, Floirac, France

We present observations of fine-structure line emission of atomic sulfur, iron, and rotational lines of molecular hydrogen in shocks associated with several Class 0 protostars obtained with the Infrared Spectrograph of the Spitzer Space Telescope. We use these observations to investigate the “missing sulfur problem,” that significantly less sulfur is found in dense regions of the interstellar medium (ISM) than in diffuse regions. For sources where the sulfur fine-structure line emission is co-spatial with the detected molecular hydrogen emission and in the presence of weak iron emission, we derive sulfur and H2 column densities for the associated molecule-dominated C-shocks. We find the S i abundance to be 5%–10% of the cosmic sulfur abundance, indicating that atomic sulfur is a major reservoir of sulfur in shocked gas. This result suggests that in the quiescent dense ISM sulfur is present in some form that is released from grains as atoms, perhaps via sputtering, within the shock.

Reference
Anderson DE, Bergin EA, Maret S and Wakelam V (2013) New Constraints on the Sulfur Reservoir in the Dense Interstellar Medium Provided by Spitzer Observations of S I in Shocked Gas. The Astrophysical Journal 779:141.
[doi:10.1088/0004-637X/779/2/141]

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Zita Martins¹, Mark C. Price², Nir Goldman³, Mark A. Sephton¹ and Mark J. Burchell²

¹Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK
²School of Physical Sciences, University of Kent, Canterbury CT2 7NH, UK
³Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, USA

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

Reference
Martins Z, Price MC, Goldman N, Sephton MA and Burchell MJ (2013) Shock synthesis of amino acids from impacting cometary and icy planet surface analogues. Nature Geoscience 6:1045–1049.
[doi:10.1038/ngeo1930]

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

Physical Sciences Department, Kingsborough Community College of the City University of New York, 2001 Oriental Boulevard, Brooklyn, New York 11235, USA

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

Reference
Howard et al. (2013) Shock synthesis of amino acids from impacting cometary and icy planet surface analogues. Nature Geoscience 6:1018–1022.
[doi:10.1038/ngeo1996]

Link to Article