Reaccumulation process after a catastrophic disruption event on a differentiated asteroid

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. • Impact simulations for a differentiated asteroid are conducted. • Smoothed particle hydrodynamic simulations with and without the material strength are used. • Rock mantle stripping and reaccumulation of fragments by the catastrophic disruption are investigated. • Reaccumulation of fragments generated by the catastrophic disruption makes iron-rich asteroids. • The surface composition differs between rubble-pile asteroids formed by mantle-stripping and those formed by reaccumulation. • Catastrophic disruption may produce iron-rich rubble-pile fragments with heterogeneous surface metal distributions, a feature that is qualitatively consistent with ALMA observations of (16) Psyche and the (22) Kalliope–Linus system.