The interpretation of decaying mass spectra from COSAC and Ptolemy on the surface of 67/P Churyumov Gerasimenko

Kurzfassung

The COSAC Instrument on Philae was operational during the first science sequence after landing on the nucleus of 67/P in November 2014. While it was unfortunately not possible to retrieve a soil sample, seven mass spectra of the gas that entered the mass spectrometer were acquired. The first mass spectrum contained the strongest signals of organic material and the results were published in SCIENCE, 31 July 2015, Vol. 349, No. 6247, DOI: 10.1126/science.aab0689. During the following six mass spectra the signals decreased and almost vanished completely. A similar set of mass spectra was acquired by the Ptolemy instrument. The decay rates of the peaks belonging to different masses were not identical over time. The ratio of the exponents obtained in an exponential fit for the count rate decay is factor of at least five between slowest and fastest decaying species. There are at least three categories. One set decays similar to the total ion count in the mass spectra, one set decays faster, and another set decays at a slower rate. Here we describe the chemical interpretation of the evolving mass spectra.