Reaccumulation process after a catastrophic disruption event on a differentiated asteroid

TL;DR

This study uses simulations to explore how differentiated asteroids break apart and form iron-rich rubble piles, providing insights into their internal structure and formation processes.

Contribution

It demonstrates that catastrophic disruption naturally produces iron-rich fragments and shows the importance of material strength and state in asteroid fragmentation.

Findings

Catastrophic disruption creates nearly compositionally similar fragments.

Largest remnants are iron-rich rubble piles formed from mixed fragments.

Material strength and state influence fragment size and disruption outcomes.

Abstract

Rubble-pile asteroids can form through the self-gravitational reaccumulation of fragments produced during large-scale collisions. To investigate how differentiated bodies are disrupted and how iron-rich rubble piles may form, we performed smoothed particle hydrodynamics simulations of impacts between differentiated asteroids with molten or solidified interiors. Our results show that catastrophic disruption produces a sheet-like structure in which core and mantle materials are stretched and subsequently fragment under self-gravity. The resulting fragments exhibit nearly identical iron-rock mass ratios, indicating that catastrophic disruption naturally generates numerous compositionally similar fragments. The largest remnant formed in such events is therefore an iron-rich rubble pile assembled from these mixed fragments, whereas remnants formed through mantle stripping retain a layered structure with an iron core and rocky mantle. We further find that fragment production is sensitive to material strength and the equation of state: mantle strength reduces the number of small fragments, while core strength suppresses catastrophic disruption when the core is solid. These results imply that iron-rich rubble-pile asteroids can form only when the iron core is molten. Our findings provide a unified framework for the formation of metal-rich asteroids such as (16) Psyche and the (22) Kalliope system, and offer predictions for the surface and internal structure that the NASA Psyche mission may test.