Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p14a..02d&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P14A-02
Other
[1028] Geochemistry / Composition Of Meteorites, [6015] Planetary Sciences: Comets And Small Bodies / Dust, [6240] Planetary Sciences: Solar System Objects / Meteorites And Tektites
Scientific paper
Sub-micron, spherical, organic globules are prevalent in primitive meteorites and interplanetary dust particles. Many of these globules are significantly enriched in 15N and/or D, relative to solar values, which suggest that they or their precursors formed in cold regions of the solar nebula or in interstellar molecular clouds. We have used correlated transmission electron microscopy (TEM), synchrotron-based X-ray absorption near-edge structure spectroscopy (XANES), and secondary ion mass spectrometry (SIMS) to determine the elemental and isotopic composition and organic functional group chemistry of individual carbonaceous nanoglobules in a suite of insoluble organic matter (IOM) residues prepared from carbonaceous and ordinary chondrites, and two additional organic globules from the Stardust comet 81P/Wild 2 sample collection. The majority of the meteoritic nanoglobules have a similar chemistry to the bulk IOM, with, on average, a small but significant enrichment in aromatic ketone (-C=O) and carboxyl (-COOH) functional groups. However, some of the meteoritic nanoglobules and one of the Stardust nanoglobules contain highly aromatic organic matter with no significant oxygen functionality. Preliminary measurements indicate that the highest 15N enrichments are associated with the highly aromatic nanoglobules and that aromatic nanoglobules are more prevalent in IOM from more primitive meteorites (e.g. Bells contains more aromatic globules than Murchison). For example, of two adjacent nanoglobules with nearly identical hollow morphologies from Murchison, one contains highly aromatic organic matter and the other contains oxidized IOM-like organic matter. SIMS analysis of these two globules reveals that the highly aromatic globule has the greatest 15N enrichment (δ15N ~ +500‰) of all meteoritic globules in which both XANES and SIMS was performed, whereas the adjacent IOM-like globule has a smaller 15N enrichment (δ15N ~ +300‰) but still greater than bulk IOM (δ15N ~ 0‰). The highly aromatic Wild 2 globule contains an even greater 15N enrichment (δ15N ~ +1100‰). The second Wild 2 globule contains a significant D enrichment, but only a terrestrial abundance of 15N. Laboratory studies of the effects of electron irradiation on the isotopic composition of organic compounds show that D, but not 15N, may be enriched due to radiation damage in some organics such as epoxy and cyanoacrylate. Aromatization of aliphatic compounds can also occur. These results indicate that measurements of functional group chemistry and D/H isotopic composition may be compromised in samples previously characterized by TEM, including the D-rich Stardust globule. The variation in morphology, chemistry, and isotopic composition of organic nanoglobules indicates the likelihood of multiple formation and alteration histories, in which parent body processing may play a significant, but not an exclusive role.
Alexander Clark
Bassim N. D.
Cody George D.
de Gregorio Bradley T.
Kilcoyne D.
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