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Compositional Analysis of Interstellar Dust as seen by the Cassini Cosmic Dust Analyzer

Fiege, Katherina

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The main goal of this thesis is to evaluate constraints on the composition of interstellar dust (ISD) grain candidates, obtained via impact ionization time-of-flight-mass spectrometry with the Cosmic Dust Analyzer (CDA) onboard the Cassini spacecraft at Saturn. For this work, spectra of 13 extremely rare ISD candidates were extracted from the vast Cassini CDA data set, based on the evaluation of their dynamical and compositional properties, namely mass, speed and trajectory. The candidates show a siliceous composition. Space-based mass spectrometers need terrestrial calibration. Therefore, we accelerated a specifically manufactured orthopyroxene dust analogue from a natural rock onto the laboratory unit of the CDA, and onto the Large Area Mass Analyzer (LAMA). The dust analogue material underwent extensive geochemical analysis with scanning electron microscope (SEM) and electron microprobe analyses (EMPA) beforehand. In the course of this study we learned that the orthopyroxene separate used as dust analogue material contains five additional minor mineral species. Using classical four-isotope geochemical plots, data show clustering at orthopyroxene composition and asymmetric directional scatter towards the minor mineral endmembers. While a significant part of the stochastic scatter can well be due to experimental artifacts, the results imply that different compositions can be distinguished. It remained unclear why many particles - though being very small in the sub-micron range - seem to occur as mixtures. Mass spectra both from CDA and LAMA, can be divided into different types according to the dominating mass line within the spectra, which are in agreement with the results from the chemical analysis performed on the LAMA spectra. Further, the types of both CDA and LAMA spectra are comparable, since they show similar features. The calibration of LAMA spectra with orthopyroxene composition determined by EMPA allowed evaluation of sensitivity coefficients, and hence, to compare the chemical signatures of the in-situ spectra of the ISD candidates with typical compositions of terrestrial silicate minerals, and cosmochemically relevant reservoirs, e.g. primitive chondritic compositions resembling unaltered solar, volatile depleted or differentiated material, which experienced Fe-loss or gain due to core formation processes. A suite of Mg-Ca-rich ISD candidates tends to primitive, only slightly volatile depleted and undifferentiated matter, while a suite of Fe rich particles is similar to reduced metal or more oxidised Fe-rich silicate material.

Item Type: Dissertation
Supervisor: Trieloff, apl. Prof. Dr. Mario
Date of thesis defense: 19 June 2013
Date Deposited: 26 Jun 2013 08:50
Date: 2013
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Dekanat der Fakultät für Chemie und Geowissenschaften
Subjects: 500 Natural sciences and mathematics
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