Formation of bi-lobed shapes by sub-catastrophic collisions: A late origin of comet 67P/C-G's structure

TL;DR

This study demonstrates that bi-lobed shapes like comet 67P/C-G can naturally form from low-energy, sub-catastrophic impacts involving elongated, rotating bodies, without significant heating or compaction.

Contribution

It introduces a new impact modeling approach showing how bi-lobed comet shapes can result from specific low-energy collisions, providing insights into comet formation.

Findings

Bi-lobed structures can form from sub-catastrophic impacts.

Such impacts do not cause major heating or compaction.

The shape of comet 67P/C-G may result from a last major impact.

Abstract

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.