Evolving properties of pits on 67P/C-G due to illumination induced mass-loss – I. Isolated shape morphology

Our aim is to characterize patterns of evolution of morphological units on the nucleus of 67P-CG such as pits, sink-holes or, more generally, pit-like features. This work focuses on developing suitable metrics to contrast different stages and changes during the time evolution. We adopt a 3D mass-loss evolution model (MONET) assuming water ice sublimation is the primary driver of erosion activity. This paper considers isolated pit-like structures without the process of merging which will be addressed in our subsequent work. The modelling study cases investigate how latitude, obliquity, and initial pit shape converge in defining the final morphology of the pits, for a spherical nucleus as well as shape model of 67P/C-G. Our results corroborate to some extent the previous studies quantifying exes heat retention due to the concavity of these pit features, however, we demonstrate a clear dependence of ‘smoothing’ or ‘deepening’ effects on the orientation and initial shape. Furthermore, it is shown that the diameter evolution of the pits is influenced by a combination of factors such as solar incidence, shadowing, and/or self-heating acting on its walls. Under certain circumstances, we also observe pronounced asymmetry in mass-loss at the pit floors, a weak effect of terracing. Mass-loss-induced evolution may result in the transformation of circular depressions into elongated ones due to specific solar illumination directions. The modelling results presented here represent the first explicit simulators of the deepening, widening, and smoothing processes in the context of 67P-C-G.