Formation of bi-lobed shapes by sub-catastrophic collisions. A late origin of comet 67P's structure

Abstract

Context. The origin of the particular shape of comet 67P/Churyumov-Gerasimenko (67P) is a topic of active research. How and when it acquired its peculiar characteristics has distinct implications on the origin of the solar system and its dynamics.
Aims: We investigate how shapes such as that of comet 67P can result from a new type of low-energy, sub-catastrophic impact involving elongated, rotating bodies. We focus on parameters potentially leading to bi-lobed structures. We also estimate the probability of such structures surviving subsequent impacts.
Methods: We used a smooth particle hydrodynamics (SPH) shock physics code to model the impacts, the subsequent re-accumulation of material and the reconfiguration into a stable final shape. The energy increase as well as the degree of compaction of the resulting bodies were tracked in the simulations.
Results: Our modelling results suggest that the formation of bi-lobed structures like 67P is a natural outcome of the low-energy, sub-catastrophic collisions considered here.
Conclusions: Sub-catastrophic impacts have the potential to alter the shape of a small body significantly, without leading to major heating or compaction. The currently observed shapes of cometary nuclei, such as 67P, may be a result of such a major shape forming impact.