A NanoSIMS and Raman spectroscopic comparison of interplanetary dust particles from comet Grigg-Skjellerup and non-Grigg Skjellerup collections

Interplanetary dust particles (IDPs) are the most primitive extraterrestrial material available for laboratory studies and may, being likely of cometary origin, sample or represent the unaltered starting material of the solar system. Here we compare IDPs from a targeted collection, acquired when the Earth passed through the dust stream of comet 26P/Grigg-Skjellerup (GSC), with IDPs from nontargeted collections (i.e., of nonspecific origin). We examine both sets to further our understanding of abundances and character of their isotopically anomalous phases to constrain the nature of their parent bodies. We identified ten presolar silicates, two oxides, one SiC, and three isotopically anomalous C-rich grains. One of seven non-GSC IDPs contains a wealth of unaltered nebula material, including two presolar silicates, one oxide, and one SiC, as well as numerous delta D and delta N-15 hotspots, demonstrating its very pristine character and suggesting a cometary origin. One of these presolar silicates is the most O-17-rich discovered in an IDP and has been identified as a possible GEMS (glass with embedded metal and sulfides). Organic matter in an anhydrous GSC IDP is extremely disordered and, based on Raman spectral analyses, appears to be the most primitive IDP analyzed in this study, albeit only one presolar silicate was identified. No defining difference was seen between the GSC and non-GSC IDPs studied here. However, the GSC collectors are expected to contain IDPs of nonspecific origin. One measure alone, such as presolar grain abundances, isotopic anomalies, or Raman spectroscopy cannot distinguish targeted cometary from unspecified IDPs, and therefore combined studies are required. Whilst targeted IDP populations as a whole may not show distinguishable parameters from unspecified populations (due to statistics, heterogeneity, sampling bias, mixing from other cometary sources), particular IDPs in a targeted collection may well indicate special properties and a fresh origin from a known source.