0000000000608619
AUTHOR
Ulrich Ott
DIRECT EVIDENCE FOR CONDENSATION IN THE EARLY SOLAR SYSTEM AND IMPLICATIONS FOR NEBULAR COOLING RATES
We have identified in an acid resistant residue of the carbonaceous chondrite Murchison a large number (458) of highly refractory metal nuggets (RMNs) that once were most likely hosted by Ca,Al-rich inclusions (CAIs). While osmium isotopic ratios of two randomly selected particles rule out a presolar origin, the bulk chemistry of 88 particles with sizes in the submicron range determined by energy dispersive X-ray (EDX) spectroscopy shows striking agreement with predictions of single-phase equilibrium condensation calculations. Both chemical composition and morphology strongly favor a condensation origin. Particularly important is the presence of structurally incompatible elements in particl…
Formation of refractory metal nuggets and their link to the history of CAIs
Abstract Ca, Al-rich inclusions (CAIs) often contain numerous refractory metal nuggets (RMNs), consisting of elements like Os, Ir, Mo, Pt and Ru. The nuggets are usually thought to have formed by equilibrium condensation from a gas of solar composition, simultaneously with or prior to oxide and silicate minerals. However, the exact mechanisms responsible for their extremely variable compositions, small sizes and associations with CAI minerals remain puzzling. Expanding on previous work on chemically separated RMNs, we have studied a large number of RMNs within their host CAIs from three different meteorite types, i.e., the highly primitive chondrite Acfer 094 (C2-ungrouped), Allende (CV3 ox…
Nondestructive full-field imaging XANES-PEEM analysis of cosmic grains
For chemical analysis of submicron particles, mass spectrometric methods have the disadvantage of being destructive. Thus, a nondestructive elemental and chemical mapping with a high spatial resolution prior to mass analysis is extremely valuable to precharacterize the sample. Here, first results are presented of combined XANES (x-ray absorption near-edge structure) and PEEM (photoemission electron microscopy) measurements on a cosmic grain fraction from the Murchison meteorite. This nondestructive full-field imaging method is well suited for a quantitative analysis and for a preselection prior to detailed mass spectrometric investigations with isotopic resolution/selectivity. A spectral un…
Trace element analysis in pre-solar stardust grains via full-field imaging XPS (Nano-ESCA)
An acid-resistant, SiC-rich, residue from the Murchison meteorite was investigated by means of a novel imaging XPS instrument. The micrometer-sized grains were deposited on a Si wafer from an aqueous suspension. Energy filtered ESCA images have been taken in the kinetic energy range from the threshold up to about 400 eV for various photon energies. A lateral resolution of the order of 120 nm along with a high energy resolution in the range of 100 meV provides the basis for chemical trace element analysis with maximum sensitivity. Apart from major (Si, C) and minor (N, Mg, Al, Fe) elements, the energy filtered images and local microspectra revealed the presence of a variety of heavy trace el…
Composition and clues to the origin of refractory metal nuggets extracted from chondritic meteorites
Refractory metal nuggets (RMNs) contain elements, such as Os, Ir, Mo, and Ru, which are predicted to condense from a cooling gas of solar composition simultaneously with CAI-minerals. Berg et al. (2009) identified a large number of RMNs in acid-resistant residues of the Murchison meteorite and suggested that they are pristine condensates. In extending the work of these authors, we have improved the chemical extraction process to enrich the concentration of RMNs in the residue sample and prepared three additional RMN-rich residues from the chondritic meteorites Murchison, Allende, and Leoville. The results show that, while their origin is clearly solar, the compositions in detail of RMNs fro…