The volatile and noble gas inventories of comets are poorly understood relative to asteroids. Interplanetary dust particles (IDPs) and micrometeorites are thought to originate predominantly from comets, therefore they provide a means of investigating cometary volatiles which can be compared to unequilibrated meteorites and help us understand the relationship between comets and asteroids. In preparation for Xe analyses, we have determined the bulk elemental compositions, H, C, N and O isotopic compositions and carbonaceous content of 26 IDPs, in order to correlate any Xe components with particular, possibly primitive cometary, characteristics. The IDPs as a whole show great heterogeneity in their mineralogy and isotopic compositions, in accordance with other studies. We observed some extreme isotopic enrichments in D and 15N, including correlations between localised D enrichments and C/H ratios, leading to a revision of the organic endmember components devised by previous authors. The Raman parameters we report also agree with other studies on the highly disordered nature of the carbon in IDPs relative to chondrites. We observed two unusual IDPs containing previously unreported features; including a Pb-chromate and large Ti-oxide grain in a highly refractory IDP, and an extremely isotopically anomalous terminus particle in a hybrid IDP; which could be an interstellar grain impact. Perhaps the most interesting particle we analysed here is composed of 50 wt% C, is highly N-rich and contains a large abundance of presolar silicates, some of which appear to be GEMS. This C-rich "ultra-carbonaceous" IDP could provide an important link to the organic material in primitive chondrites and comets. We also report the first measurement of Xe in three individually analysed IDPs, one of which is only 8 microns in diameter, and thirteen AMMs up to 150 microns in diameter. The AMMs all yielded gas, with some enabling Xe isotopic compositions to be roughly determined. These were mostly a mixture of trapped Q, solar wind and terrestrial air, with some showing 129I-derived, presolar HL and fission-derived Xe influence, similar to the range in isotopic compositions observed in chondrites. The 132Xe concentrations in the AMMs also span the range observed in chondrites. The ultra-carbonaceous, N-rich and highly isotopically anomalous IDP has yielded a 132Xe concentration, normalised to chondritic IOM content, in the same range as IOM in primitive chondrites. This suggests a possible common Q-carrier distribution in comets and asteroids, therefore further indicating wide-scale mixing in the solar nebula.
|Date of Award||1 Aug 2015|
- The University of Manchester
|Supervisor||Henner Busemann (Supervisor)|