The origin of the particular shape of a small body like comet
67P/Churyumov-Gerasimenko (67P/C-G) 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. We investigate how shapes like the
one of comet 67P/C-G can result from a new type of low-energy, sub-catastrophic
impacts involving elongated, rotating bodies. We focus on parameters
potentially leading to bi-lobed structures. We also estimate the probability
for such structures to survive subsequent impacts. We use a smooth particle
hydrodynamics (SPH) shock physics code to model the impacts, the subsequent
reaccumulation of material and the reconfiguration into a stable final shape.
The energy increase as well as the degree of compaction of the resulting bodies
are tracked in the simulations. Our modelling results suggest that the
formation of bi-lobed structures like 67P/C-G is a natural outcome of the low
energy, sub-catastrophic collisions considered here. 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/C-G, maybe a result of such a last major shape
forming impact.Comment: Astronomy & Astrophysics, accepted pending minor revision
