Carbon investigation of two Stardust particles: A TEM, NanoSIMS, and XANES study

Abstract

Abstract— In this work we present the results of a systematic search for cometary organics in 14 Stardust particles (particles from comet 81P/Wild 2, captured by NASA's Stardust mission) by TEM and multidisciplinary studies (XANES and NanoSIMS) of Febo and Ada, two of the organic‐ bearing particles identified. The combination of the three analytical techniques has established the presence of organic, cometary C in both particles. Using energy‐filtered and high‐resolution imaging it was shown that the C is amorphous and rare, given that it is found in grains ≤200 nm in size that are not abundant throughout the particles. The XANES maps and spectra of the carbonaceous areas identified with the TEM have shown that the carbonaceous material is organic due to the presence of carbonyl (C=O) functional groups and the overlapping of C and N on the same grains. In addition, several different C‐XANES spectra were obtained from the same particle, suggesting that there is diversity in the types of carbonaceous phases present in these particles, as well as a heterogeneous distribution of the carbonaceous phases within these particles. The C‐XANES spectra obtained are different from C‐XANES spectra of carbonaceous chondrites and IDPs. In the particle Febo we found five spots showing a pronounced enrichment in the isotope 15N (δ15N from 420 to 639 ± 20 to 70‰, 1s̀) that were clearly associated with the C‐rich regions. The carbonaceous material has approximately solar C and D/H isotopic compositions, and the bulk O isotopic composition was found to be s̀17 O = −18 ± 13‰ and δ18 O = −37 ± 12‰ (1s̀). In the particle Ada we found a C‐rich phase with enrichments in the isotope 15N (δ15 N = 550 ± 70 ‰, 1s̀) and the isotope D (δD = 610 ± 254‰, 1s̀). The C isotopic composition at this phase is solar (δ13 C = −4 ± 29‰, 1s̀). The bulk O isotopic composition of Ada was found to be δ17 O = 9 ± 14.6‰ and δ18 O = −7.3 ± 8.1‰ (2s̀).