Multi-correlation analyses of TOF-SIMS spectra for mineralogical studies

Abstract

A time-of-flight mass spectrometer (TOF-SIMS, COSIMA experiment) has been launched by ESA the 2nd March 2004, on board the comet bound spacecraft “ROSETTA”. The scientific objectives of COSIMA are the determination of the compositions of cometary grains as well as the molecular analyses of their exposed organic compounds. These analyses will provide inorganic and organic data for pristine solar system material, which are crucial for models of solar system formation and evolution. The challenge is, from a mass spectrum, to determine the mineral(s) analysed, to trace back the origin and formation processes of the grains which will be ultimately analysed in situ in the comet by COSIMA. To prepare the interpretation of COSIMA spectra, we have evaluated a correlation algorithm between TOF-SIMS spectra, to estimate how the information can be used to characterise the mineral phase(s) analysed. As a first step in this work, we used mineralogical samples representative of minerals found on earth and in the solar system, silicate grains. These different minerals have rather similar mass spectrum, but experienced different formation conditions in the solar nebula. We will present this correlation algorithm, allowing an accurate study of the elements responsible for the correlation, and a rapid comparison with the classical principal component analysis (PCA) method.