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Fig. 1


Top left: narrow angle camera monochromatic image (F22 filter centred at 649.2 nm) revealing a part of the Khonsu region on the comet where bluish material and exposed bright patches are present in the form of a cluster. Right: an RGB image produced with the STIFF (Bertin 2012) program using the NAC filters centred at wavelengths 882.1, 649.2, and 480.7 nm for red, green and blue colours. This image also depicts 3 regions of interest chosen for the spectrophotometric analysis. Bottom left: spectrophotometric plots of the aforementioned regions of interest are shown. Right: a zoom onto the 3 regions of interest on the RGB image is represented. The red box refers to an exposed bright patch (Deshapriya et al. 2016) containing H2 O ice, whose reflectance has been sampled (1 × 2 pixels per filter) with scrutiny to avoid saturated pixels and the blue box corresponds to H2 O ice mixed with dust and material from the nucleus (2 × 2 pixels), whereas the black box (2 × 2 pixels) represents the typical nucleus. The dimensions of the boxes are deliberately exaggerated in order to point out their respective locations on the terrain. The red and green features that sometimes appear adjacent to the shadows and near the frame edges in the RGB images are artefacts arising from the imperfect co-registration/receding shadows of the images.

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