a, b, Identified organic mass lines of individual HMOC spectra. The distribution of resolved mass lines and flank peaks of 64 HMOC spectra with the most distinct HMOCs are shown (see Methods, ‘Selection of 64 high-quality spectra for Fig. 1 and Extended Data Figs. 1 and 3’). 19 more spectra with a high level of interference with water-cluster ions or low signal-to-noise ratio are not included here (see Extended Data Table 1). All peaks depicted here are also part of the data shown in Fig. 1b. The spectrum number (as defined in Extended Data Table 1) is indicated on the left as an identifier of the event. The extent is indicated by the horizontal length and the relative normalized amplitude of each spectral feature is given by the length in the vertical direction and the colour code (red being the highest and blue the lowest amplitude). The largest horizontal span of the symbol marks the peak maximum. In b, the amplitudes between 70 u and 85 u shown in grey indicate that they are not to scale with the symbols shown at higher masses (they would be much larger; see Fig. 1b for comparison). Spectra are sorted by their impact speed, as estimated from the orbital elements of the impacting grain, with the highest speed (~15 km s−1) at the top of the graphs and the lowest (~5 km s−1) at the bottom. Because the exact orbital elements are unknown, each impact speed has substantial intrinsic uncertainties, given in Extended Data Table 1. The 12 spectra for which a minimum impact speed could be derived from the presence of hydrogen mass lines (Extended Data Table 1; see Methods, ‘Selection of 64 high-quality spectra for Fig. 1 and Extended Data Figs. 1 and 3’) are placed at the top. The highest mass at which the recording of the CDA TOF spectrum ends varies between 174 u and 226 u (Methods, ‘Short description of CDA’s chemical analyser subsystem’), as indicated by the grey horizontal bars. As a consequence, the frequency of the HMOC peaks around 178 u and 191 u in Fig. 1b is reduced because not all individual spectra cover this mass range. The absolute masses in each individual spectrum have an intrinsic uncertainty (absolute value) of ±1 u at 80 u and ±2 u at 180 u owing to the limited calibration accuracy of the CDA in this high-mass regime. The mass intervals between peaks, however, are accurate to the integer level.