). Within ρ=5000 km, the structure is extremely narrow, linear, and focused, however, it expanded to fill almost the entire southern hemisphere outside of this range. The component outside of ρ=5000 km curved toward the anti-sunward direction and dominated the FoV from ∼110◦-300◦from RFN. Surprisingly, this CN structure was remarkably similar to the dust structure designated Fan B. Wary of possible dust contamination, we ran 25 tests to determine if any residual dust had been left in the CN maps postdust-subtraction, described in Appendix section Appendix B.

We found no notable dust residuals from Fan B in the CN maps that correlated to the CN structure described above. Therefore, a strong case can be made for the correlation of Fan B dust and presence of verified CN fluorescence, which could imply that the dust particles in Fan B acted as an extended source for CN production (discussed further in Section 4). Finally, post-perihelion observations depict a symmetric CN structure that was centred around ∼165◦ from RFN, congruent with the South Pole of 67P (ϕ ≃-90◦S). Together with the dust fans, the generally unchanging morphology of NH2 and CN constitute the second domain of coma evolution we identify; (2) stable dust and gas structures. We note that our rebinning procedures reduce our spatial resolution for most pre-perihelion nights (except 30 September) to the point that we cannot definitively say that the CN signal does not evolve on small scales within the southern hemisphere, beyond what we can measure, however, we do not find evidence for such evolution at our sensitivity limits.
3.2. Dust Environment In addition to the dust maps we presented in subsection 3.1.1, we created spectral slope maps to probe the dust particle size distribution of the coma throughout the apparition. Using methods described in subsection 2.2, we were able to construct three reliable pre-perihelion and two post-perihelion maps. Due to suboptimal conditions (96% lunar illumination, 4◦lunar separation, etc.), five of our datacubes had considerable red or blue contamination that made the retrieval of the original spectral slope untenable. Therefore, we only present the maps in which conditions were mostly favourable, and no notable contamination was present. We masked out the background sky through a percentile clip in the original datacubes, in which values less than the 85th percentile were masked, seen in Figure 9. We applied 1σ smoothed contours to further highlight the distinct regimes and structures in our spectral slope maps, from 1 to 18%/1000 ˚A pre-perihelion and post-perihelion. Despite the 1σ smoothing, some hot pixels and star trails still persist in the contours, and should be ignored. Shown in Figure 9, the pre-perihelion maps depict a 6-week period in which the spectral slopes of the coma steadily evolved as 67P approached perihelion and as new regions of the nucleus became active. On 18 August, the dust coma exhibited predominantly red spectral slopes, ranging from 9%/1000 ˚A to 13%/1000 ˚A, with a central condensation containing 26 slopes exceeding 15%/1000 ˚A.

[Figure: Figure 9: Spectral slope maps from 5000-7000 ˚A, normalised 6000 ˚A, and expressed in units of %/1000 ˚A. Pre-perihelion observations are presented across the top panels, postperihelion across the bottom panels. These dates were selected based on high signalto-noise, clear atmospheric conditions, low lunar illumination, and high lunar distance. Spectral slope values on the top axis are given in a 3000 km aperture.]