Extended Data Fig. 6: CDA HMOC spectrum recorded in the Enceladean plume. | Nature

Extended Data Fig. 6: CDA HMOC spectrum recorded in the Enceladean plume.

From: Macromolecular organic compounds from the depths of Enceladus

Extended Data Fig. 6

During Cassini’s E17 flyby of Enceladus’ south pole at 75 km altitude, where the CDA recorded about 40 plume spectra with its full mass range, one spectrum was of the HMOC type. This is in agreement with the proportion of this particle type being a few per cent in the plume and in the E ring close to Enceladus (see Methods, ‘Relative frequency of HMOC-type grains depends on impact speed and distance to Enceladus orbit.’). The flyby speed determined the impact speed of 8.6 km s−1 and the particle had a radius of about 2 µm. To operate the CDA in the dense dust environment of the plume, the instrument settings had to be modified in a way that compromised the spectrum quality (lower sensitivity and lower mass resolution; see Extended Data Fig. 4 for comparison). The spectrum is baseline-corrected. On the only occasion when the CDA recorded a large number of spectra with high cadence directly in the plume during Cassini's E5 flyby9, the spectral range was truncated below about 100 u to allow for a higher data rate. This unfortunately did not allow the identification of the defining HMOC signatures.