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

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 carbonaccous 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 N-15 (delta N-15 from 420 to 639 +/- 20 to 70 parts per thousand, 1 sigma) that were clearly associated with the C-rich regions. The carbonaccous material has approximately solar C and D/H isotopic compositions, and the bulk O isotopic composition was found to be delta O-17 = -18 +/- 13 parts per thousand and (delta O-18 = -37 +/- 12 parts per thousand (1 sigma). In the particle Ada we found a C-rich phase with enrichments in the isotope N-15 (delta N-15 550 +/- 70 parts per thousand, 1 sigma) and the isotope D (delta D = 610 +/- 254 parts per thousand, 1 sigma). The C isotopic composition at this phase is solar (delta C-13 = -4 +/- 29 parts per thousand 1 sigma). The bulk O isotopic composition of Ada was found to be delta O-17 = 9 +/- 14.6 parts per thousand and delta O-18 = -7.3 +/- 8.1 parts per thousand (2 sigma).