Chan, Q. H. S.

Franchi, I. A.

Wright, I. P.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsOrganic components in interplanetary dust particlesand their implications for the synthesis of cometaryorganicsConference or Workshop ItemHow to cite:Chan, Q. H. S.; Franchi, I. A. and Wright, I. P. (2017). Organic components in interplanetary dust particlesand their implications for the synthesis of cometary organics. In: 80th Annual Meeting of the Meteoritical Society2017, 23-28 Jul 2017.For guidance on citations see FAQs.c© [not recorded]Version: Version of RecordLink(s) to article on publisher’s website:https://www.hou.usra.edu/meetings/metsoc2017/pdf/6157.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukORGANIC COMPONENTS IN INTERPLANETARY DUST PARTICLES AND THEIR IMPLICATIONS FOR THE SYNTHESIS OF COMETARY ORGANICS. Q. H. S. Chan, I. A. Franchi, and I. P. Wright, Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK. (e-mail: queenie.chan@open.ac.uk).  Introduction: The organic matter (OM) in interplanetary dust particles (IDP) is commonly associated with low-ordered organic compounds such as ketone and hydrocarbons with aliphatic and aromatic moieties [1-4]. The anhy-drous chondritic porous (CP) IDPs share a cometary origin [5], and are the most primitive astromaterial that have evaded parent body alteration processes. This study compares the organic compositions of CP-IDPs to their texture, chemical & isotopic distributions, which provides insights into the processes that led to the observed high porosity texture [6] and organic composition [7] of comet 67P/Churyumov-Gerasimenko. Samples and Methods:  Five IDPs (L2036-CA1, L2055-T1, L2055-U1, L2071-K1 and L2076-Q1) were picked by a micromanipulator and pressed flat with a spectroscopic grade sapphire window into annealed high-purity gold foils mounted on aluminium stubs. Electron images were obtained with a FEI Quanta 650 field emission gun scan-ning electron microscope at Natural History Museum London. The OM of the IDPs was analyzed by a Jobin-Yvon Horiba LabRam HR Raman microprobe with a 514 nm laser at the The Open University (OU) (laser power ≈ 60 μW). H, C, N, and O isotopic analyses were performed by a NanoSIMS 50L ion microprobe at OU.  Figure 1. EDX combined C-Mg-Al-Fe, Raman D band FWHM, and δ15N isotopic ratio maps of L2076-Q1.  Results and Discussion:  The IDPs are fine-grained, porous CP-IDPs that are composed of anhydrous minerals such as Mg-silicates and low-Ni sulphides, and display a bulk elemental composition similar to that of chondritic materials [8] (Figure 1). The ‘fluffy’ texture is similar to the grains collected in the coma of 67P [6]. C-rich phases often occur in the IDP matrix as fine-grained material around silicate grains, where the organics (e.g. polyoxymethylene on 67P [7]) could be synthesized by irradiation of preexisting ices [9], and sublimation of ices concentrated the organics for polymerization and grain surface reactions. The Raman parameters of the IDPs in this study form a continuum that span the most primitive OM to the most heated IDPs studied to date (Figure 2). The presence of magnetite rims and the degree of OM structural order of L2076-Q1 indicate that the particle has been heated during atmospheric entry, which con-trasts to the unheated Grigg–Skjellerup IDPs L2055-T1 and L2055-U1. Atmos-pheric entry heating induces a twofold heating effect on the IDP IOM. Cracking leads to fragmentation of large IOM structure into light hydrocarbons, while unshielded OM subjects to high-temperature annealing causing sp2 clustering. The Raman parameters of the IDP- and chondritic-OM are incongruent to each other. Such variation can be explained by the disordering of chondritic- OM from nanocrystalline graphite to low sp3 hydrogenated amorphous carbon, where most sp3 sites are bonded to hydrogen or heteroatoms, likely with an in-creasing H content, higher aliphatic/aromatic ratio, and reducing sp2 clus-ter/domain sizes. The enrichments in the heavy isotopes suggest that the organ-ics are indigenous to the IDPs (Figure 1; Table 1). The bulk δ15N value of L2055-T1 is typically lower than other IDPs, which also indicate that this IDP has been heated to a minimal extent as the 15N carrier is prone to thermal decomposition. References:  [1] Busemann H. et al. (2009) EPSL, 288, 44-57. [2] Clemett S.J. et al. (1993) Science, 262, 721-725. [3] Flynn G.J. et al. (2004) ASR, 33, 57-66. [4] Matrajt G. et al. (2004) A&A, 416, 983-990. [5] Brownlee D. et al. (1995) LPSC, 26.  [6] Schulz R. et al. (2015) Nature, 518, 216-218. [7] Wright I.P. et al. (2015) Science, 349. [8] Zolensky M. et al. (1993) GCA, 57, 3123-3148. [9] Bernstein M.P. et al. (1995) The Astrophysical Journal, 454, 327.    Figure 2. C Raman band parameters of the OM in the IDP samples and chondritic OM. Table 1.  Bulk isotopic compositions of the IDPs.  δ13C (‰) δ15N (‰) L2036-CA1 –45.6 ± 1.3 383.3 ± 4.6 L2055-T1 –23.7 ± 0.5 947.1 ± 2 L2055-U1 –16.5 ± 0.6 205 ± 1.9 L2071-K1 –26.8 ± 0.7 151.2 ± 2.7 L2076-Q1 –41.8 ± 0.9 279.5 ± 3.4  6157.pdf80th Annual Meeting of the Meteoritical Society 2017 (LPI Contrib. No. 1987)

Organic components in interplanetary dust particles and their implications for the synthesis of cometary organics

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