Left panel: polar transform of the spectral brightness of the smallest dust size bin of the insolation-driven outgassing model with an absorbing surface. Right panel: integrated brightness at a given radial distance multiplied by the radial distance, I(r)r, as a function of the radial distance, r, calculated according to Eq. (16). The two curves shown correspond to the smallest (8 nm, green line) and largest size bins (0.32 mm, dashed red line) that we ran. The values have been scaled relative to each other at a radial distance of 4000 m from the comet’s centre