Chemometric evaluation of time-of-flight secondary ion mass spectrometry data of minerals in the frame of future in situ analyses of cometary material by COSIMA onboard ROSETTA.

Chemometric data evaluation methods for time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been tested for the characterization and classification of minerals. Potential applications of these methods include the expected data from cometary material to be measured by the COSIMA instrument onboard the ESA mission ROSETTA in the year 2014. Samples of the minerals serpentine, enstatite, olivine, and talc have been used as proxies for minerals existing in extraterrestrial matter. High mass resolution TOF-SIMS data allow the selection of peaks from inorganic ions relevant for minerals. Multivariate cluster analysis of peak intensity data by principal components analysis and the new method CORICO showed a good separation of the mineral classes. Classification by k nearest-neighbor classification (KNN) or binary decision trees (CART method) results in more than 90% correct class assignments in a leave-one-out cross validation.

Assignment of quinone derivatives as the main compound class composing 'interstellar' grains based on both polarity ions detected by the 'Cometary and Interstellar Dust Analyser' (CIDA) onboard the spacecraft STARDUST.

The 'Cometary and Interstellar Dust Analyser' (CIDA) is a particle impact time-of-flight mass spectrometer onboard the NASA spacecraft STARDUST. A series of positive and negative ion mass spectra from the impact of (apparently) interstellar dust particles has been collected since 1999. In the meantime laboratory work has been performed to better understand the ion formation processes of organic grains impacting at those speeds (>15 km/s) and to relate them to some other ion formation methods. The key ion types were the negative ions, with some additional information from the positive ions. Here, first the principal ion formation rules are briefly reviewed. Secondly, the common substance class is inferred mainly by the application of exclusion principles, and appears to be partly condensed aromatic and quinonoid compounds with high oxygen and low nitrogen content. Oxygen appears to be present in quinone-type structures with condensed aromatic rings, possibly with furan substructures and some hydroxyl moieties. Some nitrogen may be present in pyrrole- or quinoline-type structures. Considerations of thermodynamics and radiation physics of these dust particles within the solar system are consistent with this interpretation. Quinoenzyme cofactors such as the known compound pyrroloquinoline-quinone (PQQ) and its subconstituents would be expected to yield similar mass spectra.