Morphological and spectrophotometric investigation of the layering of comet 67P/Churyumov-Gerasimenko

On 6 August 2014 the ESA’s International space mission Rosetta finally approached comet 67P/Churyumov-Gerasimenko and escorted it for the next 26 months. The particular bi-lobed shape of comet 67P suggests that it is the result of a gentle collision of two distinct bodies, which experienced a similar evolutionary history (Sierks et al., 2015). The OSIRIS imaging system provided evidence of the presence of morphological terraces that allowed the identification of thick sets of strata nearly continuous that individually envelope both lobes (Massironi et al., 2015). This pervasive layering has then been modelled by measuring the orientation of the terraces, up to define a three-dimensional ellipsoid-based model (Ellipsoidal Model, Penasa et al., 2017).

Moreover, the OSIRIS data acquired in the NUV-VIS-NIR wavelength range by the high resolution Narrow Angle camera (NAC) allowed to perform a spectrophotometric investigation of the layering, highlighting a correlation between the surface reflectance of the consolidated material of the nucleus and the structural elevation defined by the onion-shell Ellipsoidal Model. The method implies a two-classes supervised classification on the cometary surface identified as outcropping material and has been implemented separately for each lobe. The classification allowed to distinguish two major envelopes characterized by different brightness, which can be associated with different textural properties of the layers and/or a difference in the abundances of refractory materials.