The shape and structure of cometary nuclei as a result of low-velocity accretion

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Science  28 May 2015:
DOI: 10.1126/science.aaa4747

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Cometary nuclei imaged from flyby and rendezvous spacecraft show common evidence of layered structures and bi-lobed shapes. But how and when these features formed is much debated, with distinct implications for solar system formation, dynamics, and geology. We show that these features could be a direct result of accretionary collisions, based on 3D impact simulations using realistic constitutive properties. We identify two regimes of interest: layer-forming splats, and mergers resulting in bi-lobed shapes. For bodies with low tensile strength, our results can explain key morphologies of cometary nuclei, as well as their low bulk densities. This advances the hypothesis that nuclei accreted by collisional coagulation, either out of cometesimals in the early solar system, or alternatively, out of comparable-sized debris clumps paired in the aftermath of major collisions.

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