Planetary Group Seminar: Strata and envelopes of comet 67P (M. Massironi)

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 fatigue. 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. A 3D geological model, constrained by strata attitudes and equipotential surfaces of the gravity fields of the two lobes considered separately, can easily explain complex surface morphologies such as cuestas, mesas, series of stair-case terraces and persistent cliffs and provides important clues on the nucleus interior structure confirming 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 interpretation would have far-reaching consequences on how comets may have formed and evolved.