Meteorite chemistry and comparison with Rosetta comet data

The chemical composition of selected meteorites will be characterized by a combination of spectroscopic methods. Principal instrument is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) which is a twin laboratory instrument of the COmetary Secondary Ion Mass Analyzer (COSIMA), one of the instruments on board of the Rosetta mission flying towards a comet, and operated by the European Space Agency (ESA). COSIMA will analyze cometary dust grains collected in the vicinity of the comet nucleus from November 2014 onwards. These cometary dust grains are expected to have chemical similarities with carbonaceous chondrite meteorite matter, an intimate mixture of minerals and organic compounds. The results from meteorite samples will allow a more efficient and safer evaluation of the expected data from cometary matter obtained on Rosetta. Additional methods for analyzing meteorite sample surfaces in this project will be a high-performance TOF- SIMS instrument, a laser desorption/ionization tandem mass spectrometer with molecular imaging capability, an infrared microscope, and a Raman microscope. Measurement areas will have diameters between 0.001 and 0.1 mm. Meteorite samples will be selected and provided by experts of the Natural History Museum Vienna which has the largest, oldest and most diverse collection of meteorites worldwide. For the evaluation of the obtained multi-instrument data new methods from multivariate statistical data analysis will be developed and implemented in the open source programming environment "R". Development of appropriate and powerful data analysis by chemometric methods is an essential part of the project. Principal aims of the project are the characterization and classification of meteorite surfaces in analogy to the expected data from the comet. In the final part of the project also Rosetta data will be available. Several research groups will be responsibly involved in this interdisciplinary project: In Austria two institutes at the Vienna University of Technology (one for the analytical chemistry, another for the statistics), a chemistry department at the University of Natural Resources and Life Sciences in Vienna, and the Natural History Museum in Vienna. Outside of Austria will collaborate at own cost: an astrophysics group at the Max Planck Institute for Solar System Research (responsible for the COSIMA instruments), the Department of Chemistry and Material of the Swedish Technical Research Institute (high-performance TOF-SIMS), and an expert for micro meteorites and comet research at the Université Paris Sud. The planned collaborations are expected to be fruitful and will open up new avenues in space research because of past successful collaborations of project partners. The project results are expected to increase our knowledge about meteorites and asteroids. They will provide substantial support for the interpretation of Rosetta data (inorganic and organic composition of cometary matter), and will yield fundamental contributions to surface analyses and the involved chemometrics.

The space mission Rosetta of ESA (European Space Agency) was launched 2 March 2004 and reached in August 2014 the neighborhood of the comet 67P/Churyumov-Gerasimenko. In November 2014 a lander module provided measurements from the surface of the comet. Instruments onboard of Rosetta explored the comet from distances typically between 20 and 500 km for more than 2 years. One of the instruments onboard was COSIMA (COmetary Secondary Ions Mass Analyzer), developed by a group of scientists, headed by Jochen Kissel, and operated by the COSIMA team (about 30 scientists) with principal investigator (P.I.) Martin Hilchenbach, Max Planck Institute for Solar System Research (MPS), Göttingen. The chemist Kurt Varmuza (TU Wien), author of this report, was Co-P.I. of COSIMA, particularly involved in the data analysis and interpretation. The support by the FWF (P26871-N20) of the project CoMeCS (Comet and Meteorite Materials - Studied by Chemometrics of Spectroscopic Data, project investigator K. Varmuza, http://www.lcm.tuwien.ac.at/comecs/) was essential for contributions of Austrian scientists to the results derived from the COSIMA data. COSIMA collected about 1400 particles (0.02 - 0.9 mm), imaged them (1 cm 1 cm, 1024 1024 pixel) and measured about 33000 mass spectra (characterizing the chemical composition, each a table of about 128000 numbers). For comparison, several meteorite samples, provided by the Natural History Museum Wien, were measured on a laboratory twin instrument of COSIMA operated at MPS. An aim of the CoMeCS project was the development and adaptation of methods and software for multivariate statistics and machine learning - supported by the statistician Peter Filzmoser (TU Wien, Research Unit Computational Statistics). Essential results obtained from the COSIMA data are a characterization of the organic material in cometary particles as a high molecular substance, in a mixture with silicates, with atomic ratios C/Si ~5, C/H ~ 1, C/N ~ 30. Machine learning approaches found signals from carbon and hydrogen containing ions in the mass spectra, and indicated different compositions of the particles collected in different periods of the mission (with different distances to the Sun). Cometary material contains more carbon than C-rich meteorites. No distinct molecules could be identified, and no compounds could be detected related to a supposed interaction of cometary material in the development of life on Earth. The CoMeCS project resulted (in collaboration with the COSIMA team) in 14 scientific papers (2 of them in Nature), 2 PhD theses (statistics, chemistry), 4 bachelor/diploma theses, and more than 40 presentations at conferences. The developed software and a database with more than 120000 mass spectra from cometary material can be used in future studies.