The instrument COSIMA (COmetary Secondary Ion Mass Analyzer) onboard of the European Space Agency mission Rosetta collected and analyzed dust particles in the neighborhood of comet 67P/Churyumov‐Gerasimenko. The chemical composition of the particle surfaces was characterized by time‐of‐flight secondary ion mass spectrometry. A set of 2213 spectra has been selected, and relative abundances for CH‐containing positive ions as well as positive elemental ions define a set of multivariate data with nine variables. Evaluation by complementary chemometric techniques shows different compositions of sample groups collected during two periods of the mission. The first period was August to November 2014 (far from the Sun); the second period was January 2015 to February 2016 (nearer to the Sun). The applied data evaluation methods consider the compositional nature of the mass spectral data and comprise robust principal component analysis as well as classification with discriminant partial least squares regression, k‐nearest neighbor search, and random forest decision trees. The results indicate a high importance of the relative abundances of the secondary ions C+ and Fe+ for the group separation and demonstrate an enhanced content of carbon‐containing substances in samples collected in the period with smaller distances to the Sun.

中文翻译：

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在罗塞塔任务的两个时期收集的彗星粒子的组成：质谱数据的多变量评估

欧洲航天局 Rosetta 任务搭载的 COSIMA（彗星二次离子质量分析仪）仪器收集并分析了 67P/Churyumov-Gerasimenko 彗星附近的尘埃粒子。颗粒表面的化学成分通过飞行时间二次离子质谱法表征。选择了一组 2213 个光谱，含 CH 正离子和正元素离子的相对丰度定义了一组具有九个变量的多元数据。互补化学计量学技术的评估显示了在任务的两个时期收集的样本组的不同组成。第一个时期是2014年8月至11月（远离太阳）；第二个时期是 2015 年 1 月至 2016 年 2 月（离太阳较近）。应用的数据评估方法考虑了质谱数据的组成性质，包括稳健的主成分分析以及具有判别偏最小二乘回归、k-最近邻搜索和随机森林决策树的分类。结果表明次级离子 C+ 和 Fe+ 的相对丰度对于基团分离非常重要，并证明在离太阳距离较小的时期收集的样品中含碳物质的含量增加。