Extended Data Fig. 3: Comparison of CDA HMOC spectra from fast and slow impacts. | Nature

Extended Data Fig. 3: Comparison of CDA HMOC spectra from fast and slow impacts.

From: Macromolecular organic compounds from the depths of Enceladus

Extended Data Fig. 3

White and grey spectra represent the average of all spectra from impacts below and above ~10 km s−1, respectively (see Methods, ‘Selection of 64 high-quality spectra for Fig. 1 and Extended Data Figs. 1 and 3’). All signatures with possible major contributions from inorganic species are colour-shaded as in Fig. 1. Signatures not marked are exclusively or mostly due to organic cations. The abundance and position of the HMOC species is relatively independent of the impact speed of the ice grain (see also Extended Data Fig. 1). By contrast, fast impacts induce stronger organic fragmentation signatures at masses below 70 u and HMOCs form more distinct, evenly spaced groups, characteristic of impact-induced dissociation processes. In turn, slow impacts show more abundant intact benzene-like cations. There seems to be a tendency of some organic cations to carry fewer H atoms at fast impacts (27 u, 51 u and 62 u), which is indicative of ‘softer’ ionization from the slower impact. In fast spectra, interference with water-cluster ions is less frequent than at lower speeds. In contrast to fast spectra, fragmentation below \({{\rm{CH}}}_{{\rm{3}}}^{{\rm{+}}}\) (15 u) is usually not observed in slow spectra. Spectra from slow impacts are prone to abundant water clustering, creating mass lines of the form H+(H20)n, with n = 1–4, at 19 u, 37 u, 55 u and 73 u (blue). In fast spectra, clustering is limited and only the mass lines at 19 u and 37 u are generally present; occasionally, formation of the smaller water ions OH+ (17 u) and H2O+ (18 u) is observed. Similarly, Rh+ (103 u) forms from excavation of the impact target only at fast impacts and interferes with HMOC species there. To a lesser extent, this is also true for the rhodium–water cluster Rh+(H2O) at 121 u. See the individual CDA spectra in Extended Data Fig. 4 for comparison. a.u., arbitrary units; ToF, time of flight; lg, log.