FIGURE 3. Comparison of model results with Cassini data.

a, Brightness of the model plume (phase angle 153°, wavelength 750 nm) with a Cassini image from February 2005 (N1487334245_1, phase angle 153°, IR1 filter _eff = 751 nm). At this time Enceladus was near its pericentre, as it was at the time of the fly-by when the HRD data was recorded. Thus, the plume's level of activity should be comparable, if it varies with the orbital phase of Enceladus²⁷. Background brightness due to E ring dust has been subtracted (Supplementary Information). Equivalent depth—that is, brightness integrated along image lines, (I/F)dx, orthogonal to the plume axis—is plotted versus altitude (symbols). The profile of equivalent depth for the model plume, computed from Mie theory, is overplotted (lines). The brightness of the model depends mainly on collision length L_coll and condensation coefficient (see also Supplementary Figs 5 and 7). b, Cumulative particle size distribution from the model (dashed line) at the location where the HRD measured the maximal particle density (Cassini fly-by E11). The solid line includes an estimate for the background due to E ring particles^{2, 28} in the range R > 0.8 m. The number densities N of particles larger than 0.9, 1.6 and 2.8 m, respectively, derived from the in situ data², are shown as diamond symbols.