SURFACE GEOLOGY OF 67P BY ROSETTA

Since August 2014, the OSIRIS cameras provided the first detailed images of the bilobate nucleus of 67P/Churyumov-Gerasimenko comet, and the extremely variegated geomorphology of its surface became immediately clear. Most of the morphological features have been subsequently attributed to evolving processes dominated by sublimation and thermal fracturing. Erosional processes have indeed shaped the nucleus exposing terraces, persistent steep cliffs and continuous and parallel linear features. Hence, the resulting morphology appears to be structurally controlled by a primary stratification. Strata orientations have provided important clues on the nucleus interior showing that its bilobate shape is most probably the result of a gentle merging of two independent objects characterized by a primordial onion like inner structure. This geological interpreta-tion would have far reaching consequences on how comets may have formed and evolved. Thus, it is fundamental to further test the inner stratification through 3D geostructural reconstructions, analysis of possible color variegations across strata and models to unravel their resistance to slopes retreat